Showing posts with label infinite divisibility. Show all posts
Showing posts with label infinite divisibility. Show all posts

26 Dec 2017

Goldschmidt (1.1.3.14) Le système stoïcien et l'idée de temps, “Divisibilité du temps”, summary

 

by Corry Shores

 

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[The following is summary. Bracketed commentary is my own, as is any boldface. Proofreading is incomplete, which means typos are present, especially in the quotations. So consult the original text. Also, I welcome corrections to my interpretations, because I am not good enough with French or Greek to make accurate translations of the texts.]

 

 

 

Summary of

 

Victor Goldschmidt

 

Le système stoïcien et l'idée de temps

 

Première partie:

La théorie du temps et sa portée

 

A. La théorie du temps

 

III. La théorie du temps

 

1.1.3.14

Divisibilité du temps

 

 

 

Brief summary:

Chrysippus has a seemingly self-defeating notion of time. He says that no time is completely present, and yet only the present exists. This would seem to suggest that time does not exist. Chrysippus further clarifies that no time exists in the present in the strict sense rather than in the broad sense. The strict sense of the present is not something we actually experience. At best, we can form of concept of it as a limit between the past and future. Under such a conception,  we can think of the present as admitting of no past or future. But time can be said to exist in the broad sense when we think of how we experience the specious present as having some duration. So our senses tell us that there is time in the present, but this is only one sense of the term “present”, namely, the experienceable present. However, the other sense of “present,” the strict sense, is grasped not experientially but only mentally through mathematical procedures. If this sort of present has any reality, we can never actually grasp it as a real component of time. The reason for this has to do with the Stoic ideas regarding the infinite divisibility of continua, including bodies (as spatially extending things) and time (as a temporally extending and perhaps durational thing). When bodies or time are understood mathematically, we can divide them to infinity until arriving upon an infinity of indivisibles. This is already problematic, because suppose we divide a cone into an infinity of stacking circles. We begin by assuming that the cone has a smooth surface. So each ring and its neighbor cannot be of different sizes, because then the cone’s surface would be jagged. But, if they are all the same size, we have a cylinder and not a cone. We encounter a similar problem when we divide bodies and time infinitely. Suppose a body is divided into an infinity of indivisible parts. Those parts would need to lack extension, or else they would be divisible. But parts without extension cannot be parts of extending bodies, because their additive sum would not have extension. (Also, it is not clear how division can arrive upon them, because anything with extension when divided would seem to produce parts with extension, for otherwise the thing being divided would not have extension to begin with.) Similarly for time. Suppose we could infinitely divide time into instants. On the one hand, we cannot obtain indivisibles through division of divisibles. On the other hand, were we to have indivisibles of time and space, their sum could not be said to compose larger structures, because none have any extent or duration. So Chrysippus is saying that such indivisibles produced by a mathematical procedure of infinite division are beings of reason, and if they do have any reality, we can never know them in their actual reality. For in actual practice, we can only continue our divisions endlessly, never arriving upon the limit. Thus, in one sense (the broad sense) time is “real” and in anther sense (the strict sense) time is irreal (it subsists as an incorporeal something without existing corporeally).

[Note: it could instead be that time is simply real (lacking even non-existing susbistance) and the mathematical notion of infinitely divisible time is a misconception that tells us nothing about temporality itself. I will revise this if in the next section that seems to be the case, but I had the impression the next section would propose the Aiôn time which might capture the sense of the mathematical present and also the subsistence of the past and future.]

 

 

 

Contents

 

1.1.3.14

[The Divisibility of Time]

 

1.1.3.14.1

[The Non-Presence of Time and the Existence of the Present and Subsistence (Non-Existent Somethinghood) of the Past and Future]

 

1.1.3.14.2

[The Present in the Strict and Broad Sense. The Non-Presence of Time (Past and Future)]

 

1.1.3.14.3

[The Continuous Divisibility of Corporeality]

 

1.1.3.14.4

[The Mathematically Infinite Divisibility of Bodies and Time. The Impossibility of Actual Infinite Divisibility]

 

1.1.3.14.5

[Chrysippus and the Reality of Time]

 

 

 

Summary

 

1.1.3.14

Divisibilité du temps

 

1.1.3.14.1

[The Non-Presence of Time and the Existence of the Present and Subsistence (Non-Existent Somethinghood) of the Past and Future]

 

(p.37: “C’est ce qu’affirme très clairement sa thèse…”)

 

[In sum: For the Stoics, no time is completely present, and yet only the present exists, while the past and future subsist. We note the oddity here that it would seem we are to conclude that no time exists, even if the present exists.]

 

[We are continuing with Chrysippus’ definition of time as given by Stobaeus. See section 1.1.3.10.] “He says most clearly that no time is wholly present” (Long and Sedley 1987: I, 304; II, 301-302. “C’est ce qu’affirme très clairement sa thèse : aucun temps n’est entièrement présent.”) But the text continues to claim that “only the present belongs; the past and the future subsist, but belong in no way (Long and Sedley 1987: I, 304; II, 301-302) / “only the present exists, whereas the past and future subsist but do not at all exist” (Inwood & Gerson 2008: 88. “seul, le présent existe ; le passé et le futur subsistent, mais n’existent pas du tout”). Although this might seem like a contradiction, we should not think of it as such, as Stobaeus claims that Chrysippus says this “most clearly”.

« C’est ce qu’affirme très clairement sa thèse : aucun temps n’est entièrement présent. » Mais la suite du texte soutient que « seul, le présent existe ; le passé et le futur subsistent, mais n’existent pas du tout ». S’il y a là une contradiction, elle ne peut être qu’apparente, puisqu’elle se trouverait dans un même passage où le doxographe, pour sa part, ne voit rien que de « très clair ».

(37)

 

1.1.3.14.2

 

[The Present in the Strict and Broad Sense. The Non-Presence of Time (Past and Future)]

 

(p.37: “ La thèse : « Aucun temps n’est entièrement présent »…”)

 

[In sum: the present can be understood in two senses. 1) In the strict sense as the physically real present that is the limit between past and future, admitting of no parts of them. 2) In the broad sense, as the specious present we experience, where it simply appears as if in the present there is also a little bit of the past that is passing away and little bit of the future that is now coming into being. So in reality, the past and the future do not exist. They rather are sayables that can only “exist” by being expressed by thoughts in the mind.]

 

The claim that no time is entirely present is reformulated in the conclusion: “Consequently no time is present exactly, but it is broadly said to be so” (Long and Sedley 1987: I, 304; II, 301-302) / “Consequently, no time is present in the strictest sense but only in a broad sense” (Inwood and Gerson 2008: 88. In the French: “Aucun temps n’est rigoureusement présent, mais on le dit (présent) selon une certaine étendue.”) So it is in the “strict” or “exact” (“rigoureux”) sense that time is not “wholly present” (“entièrement présent”). We see the sense of this distinction in the parallel text in Stobaeus attributed to Posidonius. Here “strict” or “exact” (“rigoureux”; perhaps ἀπαρτισμὸν in the Stobaeus/Chrysippus text and in the Stobaeus/Posidonius text) means “known” / “understood” (“saisi par la pensée” and possibly “νοεῖσθαι” in the Stobaeus/Posidonius text). And “broadly” or “in a broad sense” (“en étendue” and perhaps “πλάτος” in the Stobaeus/Posidonius text) means known by perception (“perceptible” or perhaps “πρὸς αἴσθησιν” in the Stobaeus/Posidonius text). The present that Chrysippus says exists is thus a “being of reason”; so, it is quite natural in this sensualist philosophy that such a being as this does not really exist. [The English translation for this part is: “Now and the like are thought of broadly and not exactly. (5) But now is also spoken of with reference to the least perceptible time encompassing the division of the future and the past” (Long and Sedley 1987: I, 305; II, 303-304) / “And the ‘now’ and similar expressions are time understood in a broad sense and not with precision. The ‘now’ and the minimal perceptible time are established around the division between future and past” (Inwood and Gerson 2008: 86-87). The idea here seems to be the following, but I am not sure. No time exists in the exact sense means that in reality, there is no past or future that inheres in the present. But we also have a phenomenological notion of the present as having a certain thickness including a little past that is going away and a little future that is coming to be. Goldschmidt might be saying that we are to understand the present taken in the broad sense to mean the specious present of sense experience, and the present taken in the exact sense to mean the real physical present, which admits of no past or future parts (and thus has no duration).] Thus these incorporeals [the past and the present], which are sayables, only exist in thought.

La thèse : « Aucun temps n’est entièrement présent », est précisée dans la conclusion : « Aucun temps n’est rigoureusement présent, mais on le dit (présent) selon une certaine étendue. » C’est donc au sens « rigoureux », qu’aucun temps n’est « entièrement présent ». Le sens de cette distinction nous est donné dans le texte parallèle de Posidonius. « Rigoureux » signifie : « saisi par la pensée » ; « en étendue » veut dire : « saisi par la sensation »2. Le présent dont Chrysippe conteste l’existence, est donc un « être de raison » ; il est très naturel, dans cette philosophie sensualiste, qu’un tel être n’existe pas. C’est le propre de ces incorporels que sont les exprimables, que de n’exister que dans la « pensée »3.

2. Posidonius ap. Ar. Did., 26 (Dox. gr., 461, 19-21) : [See the last two sentences of the following text

Posidonius in Stobaeus 1.105,17-106,4 in Anthologium, vol.1:

Posidonius in Stobaeus 1.105.SPosidonius in Stobaeus 1.106.S

(Stobaeus 1884a: 105-106)]

3. Diog. Laërt., VII, 63 (S.V.F., II, 181) : Φασὶ δὲ [τὸ] λεκτὸν εἶναι τὸ κατὰ φαντασίαν λογικὴν ὑφιστάμενον ; cf. p. 18, n. 4-5. Et le texte de Proclus, au sujet du temps : [See the part below beginning : ἕν γὰρ ἦν τῶν παρ᾽ αὐτοῖς and ending φιλαῖς] (in Plat. Tim., 271 d = S.V.F., II, 521).

SVF 251 Proclus Plat Tim.S

(SVF II, 521, p.166)

 

 

1.1.3.14.3

 

[The Continuous Divisibility of Corporeality]

 

(pp.37-38: “La preuve de l’inexistence de ce…”)

 

[In sum: The non-existence of the present is based on the Stoic argument against Epicurean atoms. Atoms are small parts of corporeal bodies, and so they are arrived upon by division. As corporeal, they are defined as having extension. And as atomic, they are defined as being indivisible. But anything with extension is divisible, for otherwise it would lack substantiality as a corporeality. Thus atoms are both divisible and indivisible, which is absurd. There are thus no atoms, and corporeal divisibility would have to continue to infinity, never arriving upon an indivisible part.]

 

The proof of the inexistence of the present is based on the infinite divisibility of continua. This particular theory of division is borrowed from Aristotle, and we note that for the Stoics, it has primarily a polemical intention, namely, to show that, contra Epicurus, the division of bodies can continue infinitely without ever arriving upon indivisible elements that are atoms. Under this presentation of the theory, we find that it involves a reduction to absurdity. For, it shows how the atomistic conception, when applied rigorously, destroys the so-called “indivisibles” [or “unbreakables”] and thereby destroys itself. [I am not certain, but the idea might be the following, and this is a guess. Suppose there are indivisible atoms. They would be arrived upon by dividing composites. We also assume that a body is something that has some extension, for otherwise it would have no substantiality in corporeality. But whatever has extension can be divided. So atoms both have and do not have extension, which is absurd. (They have extension because they are corporeal but they do not have extension because they are indivisible.) Thus there are no atoms.]

La preuve de l’inexistence de ce présent s’appuie sur la divisibilité à l’infini des continus. Cette théorie de la division est empruntée à Aristote, et l’on admet que, chez les Stoïciens, elle procède d’une intention surtout polémique : il s’agit de montrer, contre Epicure, que la division des corps peut se poursuivre à l’infini, sans que l’on puisse jamais rencontrer ces éléments « indivisibles » que seraient les atomes4. Si telle est bien la prétention de cette théorie, elle enveloppe donc une réduction à l’absurde ; elle fait voir que la conception atomiste, appliquée rigoureusement, dé- | truit les soi-disant insécables derniers et, par là, se détruit elle-même.

4. Voir E. Bréhier, Chrysippe, p.120.

 

 

1.1.3.14.4

 

[The Mathematically Infinite Divisibility of Bodies and Time. The Impossibility of Actual Infinite Divisibility]

 

(p.38: “Cette polémique implique deux idées …”)

 

[In sum: For the Stoics, it is only mentally that we can divide bodies and time infinitely such that we arrive upon indivisibles. But in actuality, such a dividing process can never finish. Thus Chrysippus says that bodies and time are infinitely divisible (mathematically) but in actuality bodies and time are only continuously divisible, never arriving upon an infinity of indivisibles.]

 

This polemic against atomism implies two ideas: {1} that whose non-existence we wish to demonstrate are not the real elements of things but are only those elements which are indivisible and which, for Epicurus and Democritus, and deprived of any sensible quality, making them, in the eyes of the Stoics, no more than “thought” [or mentally conceived] elements. {2} the division to infinity is made using a “dianoetic” [purely intellectual] method of mathematical analyses, which is completely unable to help us grasp the real elements of things. As such, we can apply them without much difficulty to both incorporeals and corporeals, even though in both cases we are only making the divisions in thought without ever making any divisions in real being. This is what Aetius explains (as it is in Stobaeus): “Chrysippus said that bodies are divided to infinity, and likewise things comparable to bodies, such as surface, line, place, void and time. But although these are divided to infinity, a body does not consist of infinitely many bodies, and the same applies to surface, line and place [<and void and time>]” (Long and Sedley 1987: I, 297; II, 296. Bracketed insertions added in accordance with the Long and Sedley II, p.296 footnote and the French text (see the comments following footnote 4 below): “Chrysippe a dit que les corps se divisent à l’infini, de même que les choses qui ressemblent aux corps, comme la surface, la ligne, le lieu, le vide, le temps ; si ces choses se divisent à l’infini, le corps n’est pas (pour autant) composé2 de corps infinis, pas plus que la surface3, ni la ligne, ni le lieu < ni le vide, ni le temps”.) [I gather that the idea here is the following, but I am still not entirely sure. For the Stoics, we can divide bodies to infinity only using mathematical methods and by considering them as mental entities. But were we to actually divide bodies or time, that is something that would never be completed, at least in a finite amount of time. So insofar as the presumed smallest parts are only obtained by actual division, we can say that bodies and time can be divided to infinity mathematically but only infinitely divided (continuously but never to completion) in actuality.] [I note something that I find odd at this point. We are saying that in actuality bodies and time are not divisible into an infinity of indivisibles. But we are also saying that the present in reality (or at least in the strict sense) has no parts. I am not confident in my interpretation so far. But I would have thought that we would say that in the mind the present admits of parts but in reality it does not. Perhaps the idea is the following. The present really does not have parts. We can at best obtain a mathematical notion of this, because it is not possible for humans to arrive upon in actuality. However, we should be cautious with this mathematical notion, because it is only a mental construction and it does not give us the real indivisible itself.]

Cette polémique implique deux idées, d’ailleurs solidaires : a) ce dont on veut ainsi démontrer l’inexistence, ce ne sont pas les éléments réels des choses, mais uniquement ces éléments insécables, invisibles et dépourvus, pour Epicure comme pour Démocrite, de toute qualité sensible1, donc, aux yeux des Stoïciens, des éléments simplement « pensés » ; b) la division à l’infini se fait selon une méthode d’analyse mathémathique, « dianoétique », qui se révèle radicalement impuissante à nous faire saisir les éléments réels des choses. Aussi peut-on l’appliquer sans inconvénient, non seulement aux incorporels, mais encore aux corps : dans les deux cas, on ne divise qu’ « en pensée », sans entamer l’être réel. C’est ce que nous explique Aëtius : « Chrysippe a dit que les corps se divisent à l’infini, de même que les choses qui ressemblent aux corps, comme la surface, la ligne, le lieu, le vide, le temps ; si ces choses se divisent à l’infini, le corps n’est pas (pour autant) composé2 de corps infinis, pas plus que la surface3, ni la ligne, ni le lieu < ni le vide, ni le temps >4 »5.

(38)

Démocrite, in Vors6., 68 A 49 (Galien, de elem. sec. Hipp., I, 2) ; Epicure, Lettre à Hérodote, 54.

2. Cf. Plut., de comm. not., 38, 1079 b-c (S.V.F., II, 483).

3. Il faut comprendre : «  ... n’est composée de surfaces », et de même pour les autres termes de l’énumération.

4. L’addition, due à Heeren, semble s’imposer ; l’hésitation de Diels (« ceterum dubitari potest de vacui et temporis notione corporea ») ne se justifie pas ; la corporéité n’est affirmée, ni du vide, ni du temps, dans ce texte, dont la thèse principale (la divisibilité à l’infini des corps, des lieux et des temps) est corroborée par Sextus, math., X, 142 (S.V.F., II, 491).

5. Aëtius, I, 16, 4 (Dox. gr., 315, 8-15 = S.V.F., II, 482).

(38)

[Regarding note 4, I cannot follow the explanations in Latin, but let me provide them for the record:

Stobaeus. Eclogae. Heeren p.345.S

(345)

Stobaeus. Eclogae. Heeren p.344.S

(344)

Stobaeus. Eclogae. Heeren p.344.fth.S

(344)

Stobaeus. Eclogae. Heeren p.345.fth.cont.S

(Stobaeus; Heeren 1792: 344-345)

 

Stobaeus. Eclogae. In Diels Dox Gr.p315.S

Stobaeus. Eclogae. In Diels Dox Gr.p315.ft15.S

(Stobaeus; Diels, Doxographi graeci. 1879: 315)

In Long and Sedley II, the additions are given only in footnote, and in Long and Sedley I, there is no inclusion or footnote.]

 

 

1.1.3.14.5

 

[Chrysippus and the Reality of Time]

 

(pp.38-39: “On ne saurait donc conclure de notre texte …”)

 

[In sum: So Chrysippus is not arguing that time, which is continuously divisible, is divisible in actuality to indivisible parts. Were he to argue such a thing, that would mean that time is composed of durationaless points where there is neither past nor future, but only a cut between them. And such an argument would imply that time is not real. But that cannot be Chrysippus’ argument, because then by the same operation of division bodies would be composed of non-extending parts, and surely Chrysippus is not arguing that bodies are irreal. Rather, these indivisibles are attainable only through mental operations and not in reality.]

 

So even though Chrysippus speaks of the infinite divisibility of time, we should not simply conclude that he was arguing for the irreality of time. For, were he doing so, we would have to conclude that bodies are not real. [I am not certain what is meant here, so I will guess that the idea is the following. Superficially we might note that Chrysippus says that bodies and time are divisible to infinity. That would leave time being composed of parts with no temporality, because these parts at best would be like cuts within the flow from future to past. And an infinity of cuts would not make time. This cannot be right, because if Chrysippus also meant that bodies are divisible into indivisible parts, that would mean that bodies are fundamentally composed of things without extension, which is also absurd.] Later we will ask if the theory of the division of continua for Chrysippus entails a positive counterpart. But for now, we simply note that irreality is affirmed of a time or of a present that we might claim to know by a dianoetic analysis. This is similar to the reasoning Chrysippus used when discussing the parts of a cone, which Democritus criticized. For surely the Stoics did not mean to conclude that the cone does not exist. [See the discussion here. Perhaps the idea is that for Chrysippus, only in the mind would there be an infinity of depthless circles making a cone. In reality, the cone would be made of very many ribbons set at the angle of the cone’s slope.] [The last idea might be: Rather, the present is to a certain extent real, and it is grasped by sensation.] [Note 6 will be important in the next section, so let us take a look at it now:] Recall that we said that irreality is affirmed of a time or of a present that we know by mental, mathematical operations. The time that is divided to infinity is “total time,” which extends infinitely into the past and future. But the division applies also to the present, which is limited, because the division cannot stop at an indivisible instant. [If we take present, understood as having a duration, we can also divide it continuously without arriving upon a durationless instant.] This is implied in our text, and Plutarch says it formally: “this is the result for the Stoics, who do not admit a minimal time or wish the now to be partless but claim that whatever one thinks one has grasped and is considering as present is in part future and in part past.” (Plutarch, On common conceptions 1081C, from Long and Sedley I, p.304. In the French: « Ils ne veulent | pas reconnaitre un instant sans parties ; si l’on croit saisir par la pensée un présent, ils répondent que ce présent est en partie du passé, en partie, du futur ». And in the Greek: “ὅ τι ἄν τις ὡς ἐνεστὼς οἴηται λαβὼν διανοεῖσθαι, τούτου τὸ μὲν μέλλον τὸ δὲ παρῳχημένον εἶναι φάσκουσιν”.)

On ne saurait donc conclure de notre texte que Chrysippe enseignant la divisibilité à l’infini du temps, ait voulu montrer l’irréalité de celui-ci, car une conclusion analogue réduirait également à néant, la réalité des corps. Nous nous demanderons plus loin si la théorie de la division des continus ne comporte pas, chez Chrysippe, une contre-partie positive. Pour l’instant, il suffit de voir que l’irréalité est affirmée d’un temps (ou d’un présent)6 que l’on prétendrait saisir par l’analyse dianoétique, de même que sont irréels les | disques innombrables dans lesquels Démocrite avait décomposé le cône1 ; de quoi, assurément, les Stoïciens n’entendaient pas conclure que le cône même n’existait pas2. Est réel, en revanche, le présent d’une certaine étendue et saisi par la sensation.

(38-39)

6. C’est « le temps total » qui, en tant que continu, comporte la division à l’infini (le temps total, qui est infini du côté du passé et du côté de l’avenir). Mais la division, puisqu’elle ne peut s’arrêter à aucun instant indivisible, s’applique également au présent (qui, lui, est limité) ; c’est ce qu’implique notre texte même, et c’est ce que nous dit formellement Plutarque ; « Ils ne veulent | pas reconnaitre un instant sans parties ; si l’on croit saisir par la pensée un présent, ils répondent que ce présent est en partie du passé, en partie, du futur » (ὅ τι ἄν τις ὡς ἐνεστὼς οἴηται λαβὼν διανοεῖσθαι, τούτου τὸ μὲν μέλλον τὸ δὲ παρῳχημένον εἶναι φάσκουσιν), de comm. not., 41, 1081 c (S.V.F, II, 519).

(38-39. Greek text copied from Perseus)

1. Plut., de comm. not., 39, 1079 e (S.V.F, II, 489).

 

 

 

 

From:

Goldschmidt, Victor. (1953). Le système stoïcien et l'idée de temps. Paris: Vrin.

 

 

Also cited:

 

Diogenes Laertius. 1925b. Lives of Eminent Philosophers, vol.2. Translated by Robert D. Hicks. London: William Heinemann / New York: G.P. Putnam’s Sons.

http://www.perseus.tufts.edu/hopper/text?doc=Perseus%3Atext%3A1999.01.0258%3Abook%3D7%3Achapter%3D1

 

Doxographi graeci. 1879. Edited by Hermann Diels. Berlin: Reimer.

PDF available at:

https://archive.org/details/doxographigraec00dielgoog

 

Inwood, Brad, and Gerson, Loyd P. 2008. The Stoics Reader. Selected Writings and Testimonia, edited and translated by Brad Inwood and Loyd P. Gerson. Indianapolis and Cambridge: Hackett.

 

Long, Anthony A. and David N. Sedley. 1987. The Hellenistic Philosophers, vol.1: Translations of the Principle Sources, with Philosophical Commentary. Cambridge: Cambridge University Press.

 

Long, Anthony A. and David N. Sedley. 1987. The Hellenistic Philosophers, vol.2: Greek and Latin Texts with Notes and Bibliography. Cambridge: Cambridge University Press.

 

Plutarch. De communibus notitiis contra Stoicos. Taken from:

http://www.perseus.tufts.edu/hopper/text?doc=Perseus%3Atext%3A2008.01.0392%3Astephpage%3D1058f

 

Stobaeus. 1792.  Ioannis Stobaei. Eclogarum physicarum et ethicarum. Libri duo. Pars Prima. Physica continens. Edited by Arnold Heeren. Göttingen: Vandenhoeck and Ruprecht.

PDF available at:

https://books.google.com.tr/books?id=61wUAAAAQAAJ&dq=stobaeus+Heeren&source=gbs_navlinks_s

 

Stobaeus. 1884a. Ioannis Stobaei: Anthologium, vol.1. [Ioannis Stobaei, Anthologium Volumen Primum, Anthologii Librum Primum Volumen I: Libri duo Priores qui inscribi solent Eclogae Physicae et Ethicae] Edited by Kurt Wachsmuth. Berlin: Weidmann.

PDF at:

https://archive.org/details/adw8682.0001.001.umich.edu

 

SVF. 1964b. Stoicorum veterum fragmenta, vol.2: Chrysippi Fragmenta Logica et Physica. Ed.  Hans von Arnim. Stuttgart: Teubner.

PDF available at:

https://archive.org/details/stoicorumveterum02arniuoft

 

 

 

 

 

 

 

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12 Dec 2017

Goldschmidt (1.1.3.10) Le système stoïcien et l'idée de temps, “Définition”, summary

 

by Corry Shores

 

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[The following is summary. Bracketed commentary is my own, as is any boldface. Proofreading is incomplete, which means typos are present, especially in the quotations. So consult the original text. Also, I welcome corrections to my interpretations, because I am not good enough with French or Greek to make accurate translations of the texts.]

 

 

 

Summary of

 

Victor Goldschmidt

 

Le système stoïcien et l'idée de temps

 

Première partie:

La théorie du temps et sa portée

 

A. La théorie du temps

 

III. La théorie du temps

 

1.1.3.10 Définition

 

 

 

Brief summary:

For Chrysippus the Stoic, time is the interval of movement in the sense of giving measure to the motion’s speed or slowness. It is also the movement of the world by which all things not only move but also exist. For, existence  is a matter of being actually active in the present, and this furthermore is to be true, because to exist means to be an activity currently belonging to a subject. Thus “walk” truly belongs to you and thus exists when you are actually walking right now, and it does not truly belong to you and it does not exist when you are currently sitting or lying down. This also means that the past and the future do not exist. But we still say that they “subsist”. [For, they have somethinghood as incorporeals.] The present is infinitely divisible, without that infinite divisibility ever being completable. This means that any piece of time no matter how small will always include a pastmost and futuremost extremity. Thus no part of time is precisely and completely present, but it is partially so.

 

 

 

Summary

 

1.1.3.10

 

Chrysippus defines time in the following ways. {1} Time is the interval of movement, in the sense that one might consider it the measure of speed and slowness. {2} Time is the interval that accompanies the movement of the world, and it is in time that all things move and exist. However, time has two meanings, just like the earth, sea, and void. For, we can consider all four in terms of the whole or the parts. Just as the whole void is infinite in all respects, so too is the whole of time infinite at its two extremities, as the past and the future are infinite. This is clearly affirmed by Chrysippus’ thesis: no time is entirely present; for, since the division of time continues to the infinite, and since time is continuous, that means that each cut in time can be further divided infinitely. Thus no time is exactly present, but a time is said to be present in a certain extent. Chrysippus says that only the present exist, while the past and the future subsist without existing at all. Similarly, Chrissipus says that only predicates that are actual attributes exist; for example “walk” belongs to me when I am walking, but when I am lying or sitting, it does not exist.

10. « Chrysippe définit le temps : intervalle du mouvement, au sens où on l’appelle parfois mesure de la rapidité et de la lenteur ; ou encore : l’intervalle accompagnant le mouvement du monde ; et c’est dans le temps, que toutes | choses se meuvent et existent. Toutefois, le temps se prend dans deux acceptions, ainsi que la terre, la mer et le vide : (on peut en considérer) le tout ou les parties. De même que le vide total est infini de toutes parts, de même le temps total est infini à ses deux extrémités ; en effet, le passé et le futur sont infinis. C’est ce qu’affirme très clairement sa thèse : aucun temps n’est entièrement présent ; car puisque la division des continus va à l’infini, et que le temps est un continu1, chaque temps aussi comporte la division à l’infini ; en sorte qu’aucun temps n’est rigoureusement présent, mais on le dit (présent)2 selon une certaine étendue. Il soutient que, seul, le présent existe ; le passé et le futur subsistent, mais n’existent pas du tout, selon lui3 ; de la même manière, seuls, les attributs qui sont accidents (actuels) sont dits exister : par exemple, la promenade existe pour moi, quand je me promène ; mais, quand je suis couché ou assis, elle n’existe pas »4.

(30-31)

1. Litt. : « selon cette distinction » (des continus et des discontinus).

2. Le mouvement de la phrase impose cette interprétation, corroborée, au surplus, par la définition donnée par Posidonius : Τὸ δὲ νῦν καὶ τὰ ὅμοια ἐν πλάτει χρόνον καὶ οὐχὶ κατ’ἀπαρτισμὸν νοεῖσθαι. (Arius Did., 26 ; Dox. gr., 461, 19-20.)

3. Nous adoptons la conjecture de v. Arnim : φησιν. Ms : εἰσὶν; Diels : εἰ μή.

4. Arius Did . , 26 (Dox. gr., 461, 23 sqq. = S.V.F. , II, 509).

(30-31)

 

 

 

 

Other translations:

 

Chrysippus of Soli

(Χρύσιππος ὁ Σολεύς)

 

in

 

Joannes Stobaeus

(Ἰωάννης ὁ Στοβαῖο)

 

Eclogues I / Extracts I

(Eclogae I / Ἐκλογαὶ φυσικαὶ καὶ ἠθικαί)

 

1.106

(SVF 2.509)

 

Stobaeus, Eclogae I, 1.106, 5-23, part, Luhtala translation:

Only the present exists (ὑπάρχειν); the past and the future subsist (ὑφεστάναι); in the same way, as attributes (συμβεβηκότα), only the accidents are said to be the case (ὑπάρχειν); for example walking (τὸ περιπατεῖν) is true of me (ὑπάρχειν), when I walk; but when I sit or when I lie down, it is not true {οὐχ ὑπάρχει}. (SVF 2.509)

(Luhtala 2000: 113. Curly bracketed insertion is mine. See section 5.5.4.8.4)

 

Stobaeus, Eclogae I, 1.106, 5-23, Long and Sedley translation:

51B Stobaeus 1.106, 5-23 (SVF 2.509)

(1) Chrysippus said time is the dimension of motion according to which the measure of speed and slowness is spoken of; or the dimension accompanying the world's motion. (2) And (he says) every single thing moves and exists in accordance with time . . . Just as the void in its totality is infinite in every respect, so time in its totality is infinite on either side. For both the past and the future are infinite. (3) He says most clearly that no time is wholly present. For since continuous things are infinitely divisible, on the basis of this division every time too is infinitely divisible. Consequently no time is present exactly, but it is broadly said to be so. (4) He also says that only the present belongs; the past and the future subsist, but belong in no way, just as only predicates {κατηγορήματα} which are [actual] attributes {συμβεβηκότα} are said to belong, for instance, walking around belongs to me when I am walking around, but it does not belong when I am lying down or sitting.

(Long and Sedley 1987: I, 304; II, 301-302. Curly bracketed insertions mine.)

 

Stobaeus, Anthology 1.8.42 (vol. 1, pp. 105.17–106.23 W-H), Inwood and Gerson translation, part:

TEXT 44: Stobaeus Anthology 1.8.42 (vol. 1, pp. 105.17–106.23 W-H)

[...]

Chrysippus: Chrysippus says that time is the interval of motion according to which the measure of speed and slowness is sometimes spoken of; or, time is the interval which accompanies the motion of the cosmos. And each and every thing is said to move and to exist  {εἶναι} in accordance with time, unless of course time is spoken of in two senses, as are earth and sea and void and the universe and its parts. And just as void as a whole is infinite in every direction, so too time as a whole is infinite in both directions; for both the past and the future are infinite. He says most clearly that no time is wholly present; for since the divisibility of continuous things is infinite, time as a whole is also subject to infinite divisibility by this method of division. Consequently, no time is present in the strictest sense but only in a broad sense. He says that only the present exists, whereas the past and future subsist but do not at all exist— unless it is in the way that predicates are said to exist, though only those that actually apply; for example, walking ‘exists for me’ when I am walking, but when I am reclining or sitting it does not ‘exist for me’. . . .

(Inwood and Gerson 2008: 88. Curly bracketed insertions mine.)

 

Stobaeus Eclogae I p.106, 5 W. (Arii Did. fr. 26 Diels) in SVF 2.509:

Stobaeus.-SVF2.509.S_thumb1

(SVF 1964b: 164)

 

Stobaeus, Eclogae I, p.106

Stobaeus.-Eclogae.-Anthology-1.p.106

(Stobaeus 1884a: 106)

 

 

 

 

From:

Goldschmidt, Victor. (1953). Le système stoïcien et l'idée de temps. Paris: Vrin.

 

 

Also cited:

 

Inwood, Brad, and Gerson, Loyd P. 2008. The Stoics Reader. Selected Writings and Testimonia, edited and translated by Brad Inwood and Loyd P. Gerson. Indianapolis and Cambridge: Hackett.

 

Long, Anthony A. and David N. Sedley. 1987. The Hellenistic Philosophers, vol.1: Translations of the Principle Sources, with Philosophical Commentary. Cambridge: Cambridge University Press.

 

Long, Anthony A. and David N. Sedley. 1987. The Hellenistic Philosophers, vol.2: Greek and Latin Texts with Notes and Bibliography. Cambridge: Cambridge University Press.

 

Luhtala, Anneli. 2000. On the Origin of Syntactical Description in Stoic Logic. Münster: Nodus.

 

Stobaeus. 1884a. Ioannis Stobaei: Anthologium, vol.1. [Ioannis Stobaei, Anthologium Volumen Primum, Anthologii Librum Primum Volumen I: Libri duo Priores qui inscribi solent Eclogae Physicae et Ethicae] Edited by Kurt Wachsmuth. Berlin: Weidmann.

PDF at:

https://archive.org/details/adw8682.0001.001.umich.edu

 

SVF. 1964b. Stoicorum veterum fragmenta, vol.2: Chrysippi Fragmenta Logica et Physica. Ed.  Hans von Arnim. Stuttgart: Teubner.

PDF available at:

https://archive.org/details/stoicorumveterum02arniuoft

 

 

.

8 Jun 2014

Russell, Ch.41 of Principles of Mathematics, ‘Philosophical Arguments Concerning the Infinitesimal’, summary notes

 

by Corry Shores
[Search Blog Here. Index-tags are found on the bottom of the left column.]

[Central Entry Directory]

[Bertrand Russell, entry directory]

[Other entries in the Russell Principles of Mathematics, series]

[The following is summary and quotation. All boldface, underlining, and bracketed commentary are mine. Please see the original text, as I did not follow it closely. Proofreading is incomplete, so mistakes are still present.]

 


 

Bertrand Russell


Principles of Mathematics


Part 5: Infinity and Continuity


Ch.41: Philosophical Arguments Concerning the Infinitesimal





Brief Summary:

The concept of the infinitesimal as it is used in calculus involves the idea that there is a sequence of consecutive infinitely small values. But were this to be true, then there would be a one-one correspondence between the terms of one series and those of the other to which the first is being differentially related, resulting always in the ratio 1/1. However, calculus finds these differential ratios to have many values other than 1/1. So the infinitesimal leads to contradictions and must not be used in mathematics and presumably for that reason not in philosophy either.

 



Summary

 

§315


Previously Russell had argued against using the concept of the infinitesimal to account for continuity. Now he will address philosophical arguments which want to defend the infinitesimal. For this he will examine Cohen’s Princip der Infinitesimalmethode und seine Geschichte.


§316


The differential in calculus no longer needs the concept of the infinitesimal.

In the above exposition, the differential appeared as a philosophically unimportant application of the doctrine of limits. Indeed, but for its traditional importance, it would scarcely have deserved even mention. And we saw that its definition nowhere involves the infinitesimal. The dx and dy of a differential are nothing in themselves, and dy/dx is not a fraction. Hence, in | modern works on the Calculus, the notation f' (x) has replaced dy/dx, since the latter form suggests erroneous notions
[344]


But Cohen treats “the dx and the dy treated as separate entities, as real infinitesimals, as the intensively real elements of which the continuum is composed (pp. 14, 28, 144, 147).” [344] Because Cohen does not defend this concept of the infinitesimal, it seems to not be in question. “This view is certainly assumed as self-evident by most philosophers who discuss the Calculus. Let us see for ourselves what kind of grounds can be urged in its favour.” [344]


§317


Although Cohen may have understood the infinitesimals in terms of space and time, Russell will concern himself only with “such arguments as can be derived from purely numerical instances.” [344]


§318


Cohen rejects “the view that the infinitesimal calculus can be independently derived by mathematics from the method of limits.” It seems his reasoning is that (a) the method of limits presupposes a conception of equality [which is problematic for some reason, perhaps because it presupposes the idea of magnitude, but that is the second problem], and (b) the method of limits presupposes the concept of magnitude, but the concept of magnitude presupposes the concept of limit. [It may not be necessary now to fully understand how Cohen arrive at these conclusions. Russell will just show why they do not hold in mathematics.]

This method, he says (p. 1), “consists in the notion that the elementary conception of equality must be completed by the exact notion of the limit. Thus in the first place the conception of equality is presupposed. . . . Again, in the second place, the method of | limits presupposes the conception of magnitude. . . . But in the presupposed conception of magnitude the limiting magnitude is at the same time presupposed. The equality which is defined in the elementary doctrine of magnitude pays no attention to these limiting magnitudes. For it, magnitudes count as equal if and although their difference consists in a limiting magnitude. Hence the elementary conception of equality must be—this is the notion of the method of limits—not so much completed as corrected by the exact conception of the limit. Equality is to be regarded as an earlier stage of the limiting relation.”
[Russell 344-345, quoting Cohen p.1]


§319


But, Russell notes, “equality has no relevance to limits”. [Russell’s explanation for this can be found pp.345-346. He notes that the simplest concept of limit is ω, the limit of the ordinal numbers, but it does not involve the concept of equality (perhaps because it does not equal the largest of the ordinals; it is a figure above it). He gives the example of a diminishing series tending toward a value, which might seem like the sum equals the limit value, but in fact we do not need to think of it that way. See the noted pages for details.]


And Russell has already explained how magnitude is not involved in the concept of limits [limits are understood in terms of numerical series and not as series of diminishing magnitudes. See p.346 for details].


§320


[Russell then addresses the argument that magnitude presupposes the concept of limits, but limits presuppose the concept of magnitude. Yet, limits do not require the concept of magnitude. See p.346 for details.]


§321


The biggest mistake Cohen makes is that he thinks limits introduce a new meaning of equality. For magnitudes, there is only one meaning, and it does not involve the notion of approximation [no matter how close]. Cohen thinks that numbers do not have equality but only identity, which is (misleadingly) expressed using the equals sign. [Perhaps magnitudes would be two things that have identical values, and thus can be equal like two weights on a scale. But if two numbers are equal, that means they are the same number. There is not two cases of 2. There is only 2, but 2 can be expressed many ways, like 8/4. What this has to do with calculus is not so clear. But Russell goes on to say it seems that for Cohen, the infinitesimal magnitude added to a value y is equal to y because it is so close an approximation. Russell then reminds us that there is no such thing as dx and dy in calculus. Please read the text to get a more detailed understanding of Russell’s argument, pp.346-347.]

I imagine that what Cohen means may be expressed as follows. In forming a differential coefficient, we consider two numbers x and x + dx, and two others y and y + dy. In elementary Arithmetic, x and x + dx would count as equal, but not in the Calculus. There are, in fact, two ways of defining equality. Two terms may be said to be equal when their ratio is unity, or when their difference is zero. But when we allow real infinitesimals dx, x and x + dx will have the ratio unity, but will not have zero for their difference, since dx is different from absolute zero. This view, which I suggest as equivalent to Cohen’s, depends upon a misunderstanding of limits and the Calculus. There are in the Calculus no such magnitudes as dx and dy. There are finite differences Δx and Δy, but no view, however elementary, will make x equal to x + Δx. There are ratios of finite differences, Δy/Δx, and in cases where the derivative of y exists, there is one real number to which Δy/Δx can be made to approach as near as we like by diminishing Δx and Δy. This single real number we choose to denote by dy/dx; but it is not a fraction, and dx and dy are nothing but typographical parts of one symbol. There is no correction whatever of the notion of equality by the doctrine of limits; the only new element introduced is the consideration of infinite classes of terms chosen out of a series.
[347]


§322


[In the following Russell notes another of Cohen’s claims, but that claim is not explained. Perhaps it is saying that because dx and dy are infinitesimal, they do not extend in space, and thus they are inextensive. The extensive can be contrasted with the intensive. In Kant, the extensive magnitude is divisible into metrical parts, but the intensive is not. In ch.21, Russell discusses magnitudes and their measure, and he says that extensive magnitudes are numerically measurable but intensive magnitudes are not; they only admit of more or less. Also in that chapter Russell notes how for Kant, intensive magnitudes are realities that can be more or less in magnitude, like more or less bright. Let’s first look at Russell’s passage in this chapter.]

As regards the nature of the infinitesimal, we are told (p. 15) that the differential, or the inextensive, is to be identified with the intensive, and the differential is regarded as the embodiment of Kant’s category of reality.
[347]

[The differential ratio of dx to dy is inextensive for Cohen, because dx and dy are infinitesimal and thus do not extend in space. Being inextensive does not necessarily mean intensive yet. dx and dy are inextensive, as is their ratio. However, their ratio forms a quantity that is intensive, meaning that (using Russell’s definition) they are measurable in terms of being more or less but not numerically by counting parts. Kant’s concept of reality regards it as something that admits of degrees, and thus somehow the differential is the embodiment of Kant’s category of reality. I have not read Cohen yet, so I do not know his reasoning. But to give our own, we might say that Kant (especially according to a Deleuzean interpretation) regards our experiences as being experiences of reality, but these experiences are the experiences of the variations from moment to moment. We only experience degrees of difference and thus only intensities. It is only by means of recollection that we experience by means of synthesis stretches of time and the extensity of spatial objects. Thus reality in its most basic form are variations, which are understood as correlated infinitesimal differences, tiny changes over tiny moments.] [So Cohen understands dx and dy as being terms in a series, or as differences between consecutive terms. Russell will explain why they are neither, and instead they only represent stretches (series of intermediate terms) containing an infinity of terms, or “distances corresponding to such stretches”. So for Russell, dx and dy are not infinitesimals but rather merely tiny finite values that are infinitely divisible like any other finite value. Then Russell distinguishes series of numbers from series of measurable stretches or distances. Space and time, for example, are this second kind that are made of stretches or distances. But, dx and dy are not consecutive terms, because our series is compact (between any two there is another, and as we saw, there cannot be consecutive terms in a compact series, because there is no ‘next’ term; for there always is a ‘more next’ term, then another, and another, without end.) After considering some complications, Russell finds a possible way to tentatively conceive of dx and dy as being the distances of consecutive points. Russell will show why this is still absurd. He thinks it leads to the conclusion that all differential relations dx/dy would have to have the same value, either positive or negative 1. He could perhaps be saying the following. Suppose like Cohen we think that although a distance is infinitely divisible, it ultimately divides into smallest parts. These parts do not have a finite value. However, there are infinitely many such parts in a finite distance. dx and dy are thought of as such infinitesimal distances. Thus any finite distance along the x axis (or x series) is made up of an infinity of dx’s, which measure the distances between the consecutive points, and likewise for y. But the points between which dx and dy stand correlate in a one-one fashion, since these points are real values of the number line. This would seem to imply that dx and dy are always constant values, and thus dx/dy is always positive or negative one. This is because no other points intervene between them. Thus regardless of the supposed relative values of any dx/dy pairing, each themselves cannot have a value any different than the equally spaced points on which they are found, and thus must always be equal. Most likely Russell is making a different argument, which I cannot discern, so it is important to read the ‘mathematical arguments’ on page 348 for a more certain interpretation. Russell then puts these mathematical arguments aside, and says that since dx/dy have a numerical ratio, they must be numerically measurable, even though they are intensive magnitudes. (And recall that for Russell intensive magnitudes are not numerically measurable.) But Russell does not see how we might numerically measure them. So first we suppose that x and y are numbers. Then we suppose that x and x + dx are consecutive. Now, how are we to regard y + dy? We have four options. They either (a) are consecutive, (b) are identical, (c) have a finite number of terms between them, or (d) have an infinite number of terms between them. Cases c and d I think would be cases where dy is a stretch, that is, a series of terms between two end terms. Russell says that if it is a stretch, then dy/dx will always be either zero, integral, or infinite. I do not know why. Let’s suppose that these results follow from b, c, and d, as a possible way to start our explanation. If y and y + dy are identical, that means dy is 0, and making dy / dx be 0 over some other figure and thus 0. If there is a finite number of terms between y and y + dy, then that means dy/dx would have some integer value, and maybe that is what Russell means by ‘integral’. However, I do not know what he means here; if it has something to do with integral calculus I cannot discern it; and that dy/dx would have an integer value does not to me seem problematic, so I cannot interpret that. If there are an infinity of terms between y and y + dy, that means we have infinity over one (or some finite value) and thus dy/dx is infinity. In all three cases this is absurd (although the absurdity of the second case I cannot understand. It is also possible that the results “zero, or integral, or infinite” are not results of cases b, c, and d respectively.  But if that were so, I understand the situation even less.) Russell then goes on to say that even if y is not constant, dy/dx must be positive or negative 1. It seems he proves this by considering the two ways we can conceive of dy and dx, that is, as being either stretches or distances. If they were stretches, that means no matter the size of y, it will have the same size of infinity of dy-components as x has of dx-components, and they will correlate always in a one-one fashion. Since for stretches the number of terms determines the magnitude, and because the number of terms is equal and correspondent in a one-one fashion in both x and y, then dy/dx will always be 1/1. He then says that if y is not constant (sticking still with dy and dx being stretches), dy/dx will still have to be positive or negative one. He has us consider the function y = x2. And here x and y are positive real numbers. But again, if they are stretches, the same one-one correspondence will apply and thus the same problem results. Now he has us consider if we measure by distances and not stretches. He seems to be using the same reasoning. He says dy and dx are always the distance from one number to the next along the distances y and x. He then has us consider a function for which dy/dx = 2 for x = 1 and y = 1. On the one hand, the function tells us dy/dx should be two. But since there is this one-one correspondence and since x and y are equal, it would also have to be 1/1, which is absurd. This means that no matter how we conceive of consecutive values, it will lead to absurdities when applied in calculus. I would like to point out possible reasons we might not have to come to Russell’s conclusion. Russell’s argument begins by conceptualizing the infinitesimals as being the consecutive intervals between the real number values taken to be infinitely close. So under this conception, we would think that there are an infinity of infinitely small increments making up the value x and the value y, and each such increment corresponds to a real number value, which is like the total of all the infinitely small increments leading up to it. Let’s think about a geometrical interpretation, for example the curve described by y = x2. When x is 2, y is 4, and the rise/run of the tangent at that place along the curve is 4/1. Russell’s problem is that this implies that as we move to the next real number value, x + dx, we would skip over 3 points of y on the y axis, since we are jumping by 4. (In fact, since the variations are exponential, when we get to the next one, we might have jumped over even more than 4.) But that does not mean the next four real number values do not have a corresponding y value. Consider: the function says for example we are going from (2,4) to (3,9) and so on [for (x,y) coordination, with the difference between values assumed to be infinitely small]. Thus we see that we are always skipping y values when we are keeping the x values constant. However, what happens when we go up the scale of y values? What if we went from (2,4) to (x,5)? What is the value of x? Would it not also have a value, which would be between the afore-determined x-values? And as we go up the scale of y, the x values will grow relatively slower. There seems then to be an impossible contradiction if we assume consecutive infinitesimal values making up the spaces between points on the x and y axes. But perhaps there is a flaw in how Russell sets up the problem. He equates real numbers along x and y with infinitesimal increments along x and y (or along x/y). When two successive numbers are real, then there is always another between them. So there are not consecutive real numbers whose values can be assigned. The infinitesimal interval would be smaller than the interval between any givable pair of reals. So maybe we cannot, like Russell does, equate the infinitesimal increments with the real’s increments. So if we go up an infinitesimal increment along the x axis, that does not mean that it must correspond to an increment along the y which is equal in magnitude. How we are to better conceptualize such successions of infinitesimals I am not sure, but it does seem to be fairly certain that they are not equal to the succession of real numbers and thus Russell’s criticism might not hold. I have placed the entirety of this paragraph below, because it deserves a better interpretation than I can give it.]

As regards the nature of the infinitesimal, we are told (p. 15) that the differential, or the inextensive, is to be identified with the intensive, and the differential is regarded as the embodiment of Kant’s category of reality. This view (in so far as it is independent of Kant) is quoted with approval from Leibniz; but to me, I must confess, it seems destitute of all justification. It is to be observed that dx and dy, if we allow that they are entities at all, are not to be identified with single terms of our series, nor yet with differences between consecutive terms, but must be always stretches containing an infinite number of terms, or distances corresponding to such stretches. Here a distinction must be made between series of numbers and series in which we have only measurable distances or stretches. The latter is the case of space and time. Here dx and dy are not points or instants, which alone would be truly inextensive; they are primarily numbers, and hence must correspond to infinitesimal stretches or distances—for it would be preposterous to assign a numerical ratio to two points, or—as in the case of | velocity—to a point and an instant. But dx and dy cannot represent the distances of consecutive points, nor yet the stretch formed by two consecutive points. Against this we have, in the first place, the general ground that our series must be regarded as compact, which precludes the idea of consecutive terms. To evade this, if we are dealing with a series in which there are only stretches, not distances, would be impossible: for to say that there are always an infinite number of intermediate points except when the stretch consists of a finite number of terms would be a mere tautology. But when there is distance, it might be said that the distance of two terms may be finite or infinitesimal, and that, as regards infinitesimal distances, the stretch is not compact, but consists of a finite number of terms. This being allowed for the moment, our dx and dy may be made to be the distances of consecutive points, or else the stretches composed of consecutive points. But now the distance of consecutive points, supposing for example that both are on one straight line, would seem to be a constant, which would give dy/dx = ±1. We cannot suppose, in cases where x and y are both continuous, and the function y is one-valued, as the Calculus requires, that x and x + dx are consecutive, but not y and y + dy; for every value of y will be correlated with one and only one value of x, and vice versâ; thus y cannot skip any supposed intermediate values between y and y + dy. Hence, given the values of x and y, even supposing the distances of consecutive terms to differ from place to place, the value of dy/dx will be determinate; and any other function y' which, for some value of x, is equal to y, will, for that value, have an equal derivative, which is an absurd conclusion. And leaving these mathematical arguments, it is evident, from the fact that dy and dx are to have a numerical ratio, that if they be intensive magnitudes, as is suggested, they must be numerically measurable ones: but how this measurement is effected, it is certainly not easy to see. This point may be made clearer by confining ourselves to the fundamental case in which both x and y are numbers. If we regard x and x + dx as consecutive, we must suppose either that y and y + dy are consecutive, or that they are identical, or that there are a finite number of terms between them, or that there are an infinite number. If we take stretches to measure dx and dy, it will follow that dy/dx must be always zero, or integral, or infinite, which is absurd. It will even follow that, if y is not constant, dy/dx must be ±1. Take for example y = x2, where x and y are positive real numbers. As x passes from one number to the next, y must do so likewise; for to every value of y corresponds one of x, and y grows as x grows. Hence if y skipped the number next to any one of its values, it could never come back to pick it up; but we know that every real number is among the values of y. Hence y and y + dy must be consecutive, and dy/dx = 1. If we measure by distances, not stretches, the distance dy must be fixed when y is given, and the distance dx when x is given. Now if x = 1, y = 1, dy/dx = 2; but, since x and y are the same number, dx and dy must be equal, since | each is the distance to the next number: therefore dy/dx = 1, which is absurd. Similarly, if we take for y a decreasing function, we shall find dy/dx = − 1. Hence the admission of consecutive numbers is fatal to the Calculus; and since the Calculus must be maintained, the Calculus is fatal to consecutive numbers.
[347-349]


§323

 

[First Russell notes that perhaps some of the problems that have arisen result from the conceptualization of going from one term to the next being a matter of physical motion (like a point moving along the x-axis) when it is really more of a numerical progress without real temporal and spatial properties. He then goes on to challenge Cohen’s idea that inextensive infinitesimals are equatable with intensive magnitudes. To explain his reasoning for this, let’s consider first an example of an intensive magnitude, let’s say the brightness of a light. We would never say that it is smaller than some extensive magnitude. It is just a different kind of magnitude. But the infinitesimal is smaller than any extensive magnitude, and for that reason should not be considered intensive.]


§324


[In this last paragraph, Russell sums up his argument so far against infinitesimals: they are (1) unnecessary (because they are not needed for calculus), (2) erroneous (because he showed in a prior chapter that they are obtained through an “illegitimate use of mathematical inductions) and (3) self-contradictory (because they lead to such contradictions as the one mentioned above regarding their consecutivity).]

We cannot, then, agree with the following summary of Cohen’s theory (p. 28): “That I may be able to posit an element in and for itself, is the desideratum, to which corresponds the instrument of thought reality. This instrument of thought must first be set up, in order to be able to enter into that combination with intuition, with the consciousness of being given, which is completed in the principle of intensive magnitude. This presupposition of intensive reality is latent in all principles, and must therefore be made independent. This presupposition is the meaning of reality and the secret of the concept of the differential.” What we can agree to, and what, I believe, confusedly underlies the above statement, is, that every continuum must consist of elements or terms; but these, as we have just seen, will not fulfil the function of the dx and dy which occur in old-fashioned accounts of the Calculus. Nor can we agree that “this finite” (i.e. that which is the object of physical science) “can be thought as a sum of those infinitesimal intensive realities, as a definite integral” (p. 144). The | definite integral is not a sum of elements of a continuum, although there are such elements: for example, the length of a curve, as obtained by integration, is not the sum of its points, but strictly and only the limit of the lengths of inscribed polygons. The only sense which can be given to the sum of the points of the curve is the logical class to which they all belong, i.e. the curve itself, not its length. All lengths are magnitudes of divisibility of stretches, and all stretches consist of an infinite number of points; and any two terminated stretches have a finite ratio to each other. There is no such thing as an infinitesimal stretch; if there were, it would not be an element of the continuum; the Calculus does not require it, and to suppose its existence leads to contradictions. And as for the notion that in every series there must be consecutive terms, that was shown, in the last chapter of Part III, to involve an illegitimate use of mathematical induction. Hence infinitesimals as explaining continuity must be regarded as unnecessary, erroneous and self-contradictory.
[350]



 

Source:

Bertrand Russell. Principles of Mathematics. London/New York: Routledge, 2010 [1st published 1903].



4 May 2014

Russell, Ch.40 of Principles of Mathematics, ‘The Infinitesimal and the Improper Infinite’, summary notes



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[The following is summary and quotation. All boldface, underlining, and bracketed commentary are mine. Please see the original text, as I did not follow it closely. Proofreading is incomplete, so mistakes are still present.]

 
Bertrand Russell

Principles of Mathematics

Part 5: Infinity and Continuity

Ch.40: The Infinitesimal and the Improper Infinite





Brief Summary:
The infinitesimal was once an important concept in mathematics, especially for understanding continuity. Now that we have Cantor’s more precise definition of infinity, we find that the infinitesimal is found only in very special cases and it has not usefulness in mathematics anymore. Something can be infinitesimal with regard to something much greater than it. For example the side of a square is infinitesimal in relation to its area. However, mathematics considers these two sorts of magnitude as of different kinds and as being incomparable. This is the only actual instance of infinitesimals, and it has no mathematical importance. Infinitesimals were traditional understood however as absolute and not as relative as in this case. Russell shows that an absolute infinitesimal cannot exist. For example, if we divide a segment more and more, we keep getting finite valued parts, which can be summed to obtain the value of the whole. But if the parts get below the finite, then they can no longer be added to obtain a finite value. If we add an infinitely long segment to another, we do not increase its cardinal value. It will be infinite. Likewise, if we add one infinitesimal to another, it will also not become finite. Thus, a finite segment cannot be made of infinitesimals. Hence a magnitude could not be absolutely infinitesimal.


Summary

§309

Until recently (ca. 1900), continuity was understood by means of the concept of the infinitesimal. But now that concept has been abandoned. [336]

The infinitesimal has been given certain senses, but none have been mathematically precise. It is for example the distance between a point and its immediate neighbor. But we now know that there is no such thing.
The infinitesimal has, in general, been very vaguely defined. It has been regarded as a number or magnitude which, though not zero, is less than any finite number or magnitude. It has been the dx or dy of the Calculus, the time during which a ball thrown vertically upwards is at rest at the highest point of its course, the distance between a point on a line and the next point, etc., etc. But none of these notions are at all precise. The dx and dy, as we saw in the last chapter, are nothing at all: dy/dx is the limit of a fraction whose numerator and denominator are finite, but is not itself a fraction at all. The time during which a ball is at rest at its highest point is a very complex notion, involving the whole philosophic theory of motion; in Part VII we shall find, when this theory has been developed, that there is no such time. The distance between consecutive points presupposes that there are consecutive points—a view which there is every reason to deny. And so with most instances—they afford no precise definition of what is meant by the infinitesimal.
[336]


§310

[We should first examine the axiom of Archimedes. We want to know if two values are finite in relation to one another or infinite in relation to one another. Consider values 4 and 6. We can multiply 4 by 2 and get 8, which is larger than 6. This means they are finite in relation to one another, or their difference in value is finite. Now consider 4 and the cardinal value for the natural numbers. Or let’s just say, consider 4 and infinity. There is no finite number that we can multiply 4 by in order to obtain a number greater than infinity. That means they are infinite in relation to one another, or their difference is infinite. So the first example illustrates relative finitude. Absolute finitude would require some anchoring points you say, 0 and 1, and as well a principle of composing finite numbers, namely mathematical induction, the successor function. As we can see, the notion of relative finitude applies to any kind of magnitude, but absolute infinity has more limited application to numbers, classes and divisibilities. And also note that an inch and a foot both are magnitudes consisting of an infinity of terms (leading up to their total value, all the sizes smaller than an inch that are implicitly contained within it). So both an inch and a foot are absolute infinities. However, they are finite in relation to one another and are thus relative finitudes. So “any two numbers, classes, or divisibilities, which are both absolutely finite are also relatively finite; but the converse does not hold”.]
There is, so far as I know, only one precise definition, which renders the infinitesimal a purely relative notion, correlative to something arbitrarily assumed to be finite. When, instead, we regard what had been taken to be infinitesimal as finite, the correlative notion is what Cantor calls the improper infinite (Uneigentlich-Unendliches). The definition of the relation in question is obtained by denying the axiom of Archimedes, just as the transfinite was obtained by denying mathematical induction. If P, Q be any two numbers, or any two measurable magnitudes, they are said to be finite with respect to each other when, if P be the lesser, there exists a finite integer n such that nP is greater than Q. The existence of such an integer constitutes the axiom of Archimedes and the definition of relative finitude. It will be observed that it presupposes the definition of absolute finitude among numbers—a definition which, as we have seen, depends upon two points, (1) the connection of 1 with the logical notion of simplicity, or of 0 with the logical notion of the null-class; (2) the principle of mathematical induction. The notion of relative finitude is plainly distinct from that of absolute finitude. The latter applies only to numbers, classes and divisibilities, whereas the former applies to any kind of measurable magnitude. Any two numbers, classes, or divisibilities, which are both absolutely finite are also relatively finite; but the converse does not hold. For example, ω and ω.2, an inch and a foot, a day and a year, are relatively finite pairs, though all three consist of terms which are absolutely infinite.
[337]

[Russell will now definite the infinitesimal and improper infinite. Consider 2 values. If no matter what finite value we multiply one by that it can in no case be greater than the other, then this term is infinitesimal or improperly infinite. This can only apply to numbers and not magnitudes.]
The definition of the infinitesimal and the improper infinite is then as follows. If P, Q be two numbers, or two measurable magnitudes of the same kind, and if, n being any finite integer whatever, nP is always less than Q, then P is infinitesimal with respect to Q, and Q is infinite with respect to P. With regard to numbers, these relative terms are not required; for if, in the case supposed, P is absolutely finite, then Q is absolutely infinite; while if it were possible for Q to be absolutely finite, P would be absolutely infinitesimal—a case, however, which we shall see reason to regard as impossible. Hence I shall assume in future that P and Q are not numbers, but are magnitudes of a kind of which some, at least, are numerically measurable. It should be observed that, as regards magnitudes, the axiom of Archimedes is the only way of defining, not only the infinitesimal, but the infinite also. Of a magnitude not numerically measurable, there is nothing to be said except that it is greater than some of its kind, and less than others; but from such propositions infinity cannot be obtained. Even if there be a magnitude greater than all others of its kind, there is no reason for regarding it as infinite. Finitude and infinity are essentially numerical notions, and it is only by relation to numbers that these terms can be applied to other entities.
[337]


§311

[Russell will now consider instances of infinitesimal values. We first consider divisible magnitudes. If we compare something with a finite number of parts to one with an infinite number, than the first is infinitesimal in relation to it. But we cannot compare such magnitudes on the basis of placing into a ratio the cardinal numbers of their parts. Russell gives two reasons. The first is that we cannot place transfinite values into ratios (his explanation begins with saying we cannot place two transfinite cardinals into ratios. His example is of a finite and a transfinite. So for some reason it still applies in this other case). He second reason is equally unclear, but it seems he is saying that in order to make our original comparison, the divisibilities of each magnitude must be equal, but that is not the case for the transfinite value for some reason. Here is the text:]
The next question to be discussed is: What instances of infinitesimals are to be found? Although there are far fewer instances than was formerly | supposed, there are yet some that are important. To begin with, if we have been right in regarding divisibility as a magnitude, it is plain that the divisibility of any whole containing a finite number of simple parts is infinitesimal as compared with one containing an infinite number. The number of parts being taken as the measure, every infinite whole will be greater than n times every finite whole, whatever finite number n may be. This is therefore a perfectly clear instance. But it must not be supposed that the ratio of the divisibilities of two wholes, of which one at least is transfinite, can be measured by the ratio of the cardinal numbers of their simple parts. There are two reasons why this cannot be done. The first is, that two transfinite cardinals do not have any relation strictly analogous to ratio; indeed, the definition of ratio is effected by means of mathematical induction. The relation of two transfinite cardinals α, γ expressed by the equation αβ = γ bears a certain resemblance to integral ratios, and αβ =γδ may be used to define other ratios. But ratios so defined are not very similar to finite ratios. The other reason why infinite divisibilities must not be measured by transfinite numbers is, that the whole must always have more divisibility than the part (provided the remaining part is not relatively infinitesimal), though it may have the same transfinite number. In short, divisibilities, like ordinals, are equal, so long as the wholes are finite, when and only when the cardinal numbers of the wholes are the same; but the notion of magnitude of divisibility is distinct from that of cardinal number, and separates itself visibly as soon as we come to infinite wholes.
[337-338]

We can even have examples where one thing is infinitely less divisible than another, as for example a line compared to a square. [This is an example of an infinitesimal. But it seems Russell is saying that they are just relative infinitesimals and not the kind we are more concerned with, like in the infinitesimal calculus.]
Two infinite wholes may be such that one is infinitely less divisible than the other. Consider, for example, the length of a finite straight line and the area of the square upon that straight line; or the length of a finite straight line and the length of the whole straight line of which it forms part (except in finite spaces); or an area and a volume; or the rational numbers and the real numbers; or the collection of points on a finite part of a line obtainable by von Staudt’s quadrilateral construction, and the total collection of points on the said finite part.* All these are magnitudes of one and the same kind, namely divisibilities, and all are infinite divisibilities; but they are of many different orders. The points on a limited portion of a line obtainable by the quadrilateral construction form a collection which is infinitesimal with respect to the said portion; this portion is ordinally infinitesimal† with respect to any bounded area; any bounded area is ordinally infinitesimal with respect to any bounded volume; and any bounded volume (except in finite spaces) is ordinally infinitesimal with respect to all space. In all these cases, the word infinitesimal is used strictly according to the above definition, obtained from the axiom of Archimedes. What makes these various | infinitesimals somewhat unimportant, from a mathematical standpoint, is, that measurement essentially depends upon the axiom of Archimedes, and cannot, in general, be extended by means of transfinite numbers, for the reasons which have just been explained. Hence two divisibilities, of which one is infinitesimal with respect to the other, are regarded usually as different kinds of magnitude; and to regard them as of the same kind gives no advantage save philosophic correctness. All of them, however, are strictly instances of infinitesimals, and the series of them well illustrates the relativity of the term infinitesimal.
[338-339]

[Russell examines another example of comparing magnitudes divided infinitely. It is not clear to me, but it seems to be saying that if the divisions of a magnitude get smaller than the finite, then if we add up all their values, it will be 0. But please read it for yourself to decide what it means.]
An interesting method of comparing certain magnitudes, analogous to the divisibilities of any infinite collections of points, with those of continuous stretches is given by Stolz,* and a very similar but more general method is given by Cantor.† These methods are too mathematical to be fully explained here, but the gist of Stolz’s method may be briefly explained. Let a collection of points x' be contained in some finite interval a to b. Divide the interval into any number n of parts, and divide each of these parts again into any number of parts, and so on; and let the successive divisions be so effected that all parts become in time less than any assigned number δ. At each stage, add together all the parts that contain points of x' . At the mth stage, let the resulting sum be Sm. Then subsequent divisions may diminish this sum, but cannot increase it. Hence as the number of divisions increases, Sm must approach a limit L. If x' is compact throughout the interval, we shall have L = b − a; if any finite derivative of x' vanishes, L = 0. L obviously bears an analogy to a definite integral; but no conditions are required for the existence of L. But L cannot be identified with the divisibility; for some compact series, e.g. that of rationals, are less divisible than others, e.g. the continuum, but give the same value of L.
[339]


§312

[Normally we think of the infinitesimal as composing a dense or ‘compact’ series. For, if all its parts were finite and there are infinitely many, than the whole segment would be infinite. If the parts were 0, then it would have 0 value. But if there were infinitely many infinitely small part, then those infinitive values would cancel one another generating a finite value. Russell will show that either it is impossible for the parts to be infinitesimal or at least that if they were, they would be indefinable. First he establishes that any segment is infinitely divisible, because between any two values is another. Next, he explains that segments can be added by placing one at the end of the other, which increases the total magnitude. If the added segments are equal, the new total will be double. Segments without terminal endings included in them (where they tend toward limits without attaining them), we can add them by adding such terminal segments. So we can define any finite multiple of segments (by adding them). For some reason, it seems we will draw these conclusions: if a smaller segment obeys the axiom of Archimedes with respect to the larger (if no matter how many times we multiply it, it will not be greater than the larger), then the larger will contain all the terms coming after the smaller. However, if the smaller is infinitesimal with respect to larger ones, then the larger one will not contain points of the first segment. (This is too unclear for me to understand). (It seems now we are working with the idea that an infinite segment cannot be increased by doubling it. Only terminating segments can.) Thus the larger segment is not terminating. On account of this, for some reason Peano concludes that the larger segment cannot be an element in finite magnitudes. Russell draws a stronger conclusion. an infinitesimal cannot have determinate bounds. So it cannot be added so to produce larger segments. Consult the original text:]
The case in which infinitesimals were formerly supposed to be peculiarly evident is that of compact series. In this case, however, it is possible to prove that there can be no infinitesimal segments,‡ provided numerical measurement be possible at all—and if it be not possible, the infinitesimal, as we have seen, is not definable. In the first place, it is evident that the segment contained between two different terms is always infinitely divisible; for since there is a term c between any two a and b, there is another d between a and c, and so on. Thus no terminated segment can contain a finite number of terms. But segments defined by a class of terms may (as we saw in Chapter 34) have no limiting term. In this case, however, provided the segment does not consist of a single term a, it will contain some other term b, and therefore an infinite number of terms. Thus all segments are infinitely divisible. The next | point is to define multiples of segments. Two terminated segments can be added by placing a segment equal to the one at the end of the other to form a new segment; and if the two were equal, the new one is said to be double of each of them. But if the two segments are not terminated, this process cannot be employed. Their sum, in this case, is defined by Professor Peano as the logical sum of all the segments obtained by adding two terminated segments contained respectively in the two segments to be added.* Having defined this sum, we can define any finite multiple of a segment. Hence we can define the class of terms contained in some finite multiple of our segment, i.e. the logical sum of all its finite multiples. If, with respect to all greater segments, our segment obeys the axiom of Archimedes, then this new class will contain all terms that come after the origin of our segment. But if our segment be infinitesimal with respect to any other segment, then the class in question will fail to contain some points of this other segment. In this case, it is shown that all transfinite multiples of our segment are equal to each other. Hence it follows that the class formed by the logical sum of all finite multiples of our segment, which may be called the infinite multiple of our segment, must be a non-terminated segment, for a terminated segment is always increased by being doubled. “Each of these results”, so Professor Peano concludes, “is in contradiction with the usual notion of a segment. And from the fact that the infinitesimal segment cannot be rendered finite by means of any actually infinite multiplication, I conclude, with Cantor, that it cannot be an element in finite magnitudes” (p. 62). But I think an even stronger conclusion is warranted. For we have seen that, in compact series, there is, corresponding to every segment, a segment of segments, and that this is always terminated by its defining segment; further that the numerical measurement of segments of segments is exactly the same as that of simple segments; whence, by applying the above result to segments of segments, we obtain a definite contradiction, since none of them can be unterminated, and an infinitesimal one cannot be terminated.
[339-340]

[Next Russell will argue that rational and real numbers cannot be made of infinitesimals. He seems to be saying that the real numbers are made of rational numbers. The real numbers are a class of real numbers. So any member of them will as well contain rational numbers, no matter how small. But an infinitesimally small term does not contain with in any rational numbers, because it is too small. Hence the real numbers cannot be made of infinitesimals. He might very well be saying something else, so please consider the original:]
In the case of the rational or the real numbers, the complete knowledge which we possess concerning them renders the non-existence of infinitesimals demonstrable. A rational number is the ratio of two finite integers, and any such ratio is finite. A real number other than zero is a segment of the series of rationals; hence if x be a real number other than zero, there is a class u, not null, of rationals such that, if y is a u, and z is less than y, z is an x, i.e. belongs to the segment which is x. Hence every real number other than zero is a class containing rationals, and all rationals are finite; consequently every real number is finite. Consequently if it were possible, in any sense, to speak of infinitesimal numbers, it would have to be in some radically new sense.
[340]


§313

[Russell now examines an interesting question regarding orders of infinity and infinitesimality of functions. Russell does not draw any conclusions (although he seems to want at the end to say that this material supports the notion that infinitesimals are mathematical fictions), so I will just place the very technical material below:]
I come now to a very difficult question, on which I would gladly say nothing—I mean, the question of the orders of infinity and infinitesimality of functions. On this question the greatest authorities are divided: Du Bois Reymond, Stolz, and many others, maintaining that these form a special class of magnitudes, in which actual infinitesimals occur, while Cantor holds strongly that the whole theory is erroneous. To put the matter as simply as possible, consider a function f(x) whose limit, as x approaches zero, is zero. It may happen that, for some finite real number α, the ratio f(x)/xα has a finite limit as x approaches zero. There can be only one such number, but there may be none. Then α, if there is such a number, may be called the order to which f(x) becomes infinitesimal, or the order of smallness of f(x) as x approaches zero. But for some functions, e.g. 1/log x, there is no such number α. If α be any finite real number, the limit of 1/xα logx, as x approaches zero, is infinite. That is, when x is sufficiently small, 1/xα log x is very large, and may be made larger than any assigned number by making x sufficiently small—and this whatever finite number α may be. Hence, to express the order of smallness of 1/log x, it is necessary to invent a new infinitesimal number, which may be denoted by 1/g. Similarly we shall need infinitely great numbers to express the order of smallness of (say) e−1/x as x approaches zero. And there is no end to the succession of these orders of smallness: that of 1/log (log x), for example, is infinitely smaller than that of 1/log x, and so on. Thus we have a whole hierarchy of magnitudes, of which all in any one class are infinitesimal with respect to all in any higher class, and of which one class only is formed of all the finite real numbers.
In this development, Cantor finds a vicious circle; and though the question is difficult, it would seem that Cantor is in the right. He objects (loc. cit.) that such magnitudes cannot be introduced unless we have reason to think that there are such magnitudes. The point is similar to that concerning limits; and Cantor maintains that, in the present case, definite contradictions may be proved concerning the supposed infinitesimals. If there were infinitesimal numbers j, then even for them we should have
Limx = 0 1/ (log x. xj) = 0
since xj must ultimately exceed ½. And he shows that even continuous, differentiable and uniformly growing functions may have an entirely ambiguous order of smallness or infinity: that, in fact, for some such functions, this order oscillates between infinite and infinitesimal values, according to the manner in which the limit is approached. Hence we may, I think, conclude that these | infinitesimals are mathematical fictions. And this may be reinforced by the consideration that, if there were infinitesimal numbers, there would be infinitesimal segments of the number-continuum, which we have just seen to be impossible. [341-342]


§314

[Russell now summarizes. He has shown that the infinitesimal can never be anything but a relative term. When it does have an absolute meaning, it is indistinguishable from finitude (perhaps this is from the idea that an infinitely small segment cannot be increased by doubling it, so were a segment made of infinitesimals, they would have to have the properties of finite magnitudes.) There are cases of infinitesimals, for example the side of a square is infinitesimal compared with its area. But mathematicians consider each magnitude as different in kind and thus incomparable. We also saw that compact (dense) series cannot be made of infinitesimals. Thus the infinitesimal has not many important manifestations and it is not important mathematically.]
Thus to sum up what has been said concerning the infinitesimal, we see, to begin with, that it is a relative term, and that, as regards magnitudes other than divisibilities, or divisibilities of wholes which are infinite in the absolute sense, it is not capable of being other than a relative term. But where it has an absolute meaning, there this meaning is indistinguishable from finitude. We saw that the infinitesimal, though completely useless in mathematics, does occur in certain instances—for example, lengths of bounded straight lines are infinitesimal as compared to areas of polygons, and these again as compared to volumes of polyhedra. But such genuine cases of infinitesimals, as we saw, are always regarded by mathematics as magnitudes of another kind, because no numerical comparison is possible, even by means of transfinite numbers, between an area and a length, or a volume and an area. Numerical measurement, in fact, is wholly dependent upon the axiom of Archimedes, and cannot be extended as Cantor has extended numbers. And finally we saw that there are no infinitesimal segments in compact series, and—what is closely connected—that orders of smallness of functions are not to be regarded as genuine infinitesimals. The infinitesimal, therefore—so we may conclude—is a very restricted and mathematically very unimportant conception, of which infinity and continuity are alike independent. [342]


 
Sources [unless otherwise noted, all bracket page citations are from]:
Bertrand Russell. Principles of Mathematics. London/New York: Routledge, 2010 [1st published 1903].