1 Feb 2017

Sambursky (1.1) Physics of the Stoics, “Pneuma and Coherence”, selective summary


by Corry Shores


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[The following is a selective summary, meaning that I select certain ideas to discuss rather than thoroughly summarize the text. All bracketed commentary and boldface is mine. Proofreading is incomplete, so you will encounter distracting typos. I apologize in advance.]





Samuel Sambursky


Physics of the Stoics



The Dynamic Continuum


1.1 Pneuma and Coherence


Selective summary



Brief summary [of selected ideas]:

The Stoics held that the cosmos is a continuous whole surrounded by a void. The continuity of the whole is a dynamic continuity resulting from a cohering activity of a very rarified substrate called pneuma. Pneuma is composed of a mixture of the active elements, Air and Fire, while Water and Earth are the other two passive elements that pneuma serves to bind. Pneuma has two physical features that give it this cohering role: {1} tonos, the tension which holds things together, and {2} gravitational neutrality, which means it gathers neither too high nor too low but instead equally pervades all domains of the cosmos.



Selective summary


For the Stoics, the cosmos is a continuous whole surrounded by a void. The coherence of its continuity stems from its substratum of pneuma, whose role is to create cohesion between the parts of matter in the cosmos.

According  to the Stoic conception, the cosmic scene of  material events, including conglomerate matter as well as space between bodies, is made up of a continuous whole. Like Aristotle, the Stoics exclude emphatically any possible existence of a void within the cosmos.1 However, their cosmos is, in contradiction to that of Aristotle, an island embedded in an infinite void.2 The cosmos is filled with an all-pervading substratum called pneuma, a term often used synonymously with air.3 A basic function of the pneuma is the generation of the cohesion of matter and generally of the contact between all parts of the cosmos. The term coherence was originally used by Aristotle to express continuity in an essentially geometrical and topological sense,4 but the Stoics gave it the physical and dynamic significance of cohesion within the physical world.

1. Diog. Laert., VII, 140; Cleom., De motu circulari, I, 1 (ed. Ziegler), p. 8.

2. Plut., De Stoic. repugn., 1054 b, says that this theory was repeatedly mentioned in Chrysippos’ writings.

3. e.g. Plut., loc. cit., 1053 f.

4. Arist., Metaph., 1069 a 6; cf. also Metaph., 1061 a 33. See p. 5 in connection with Metaph., 1015 b 36. For pre-Socratic origins of συνέχεια, cf. Parmenides (Diels, 28 B 8, 25): τῷ ξυνεχὲς πᾶν ἐστιν, ἐὸν γὰρ ἐόντι πελάζει.



Pneuma can be understood in biological terms as being like breath, which mixes the cold air with the heat of the body:

As air represents the principle of Cold, the warmth of the human body makes it likely that the stuff souls are made of is a mixture of cold and hot, of air and fire. [...] the Stoics expanded the idea of mixture by adding the other two qualities of Dry and Moist, thus making possible the differentiation between the pneuma of the soul (psyche) and that of the world of plants (physis). The former is dry and warm whereas the pneuma of physis is moist and cold.



Of the four elements, the Stoics classify “Air and Fire as active, and Earth and Water as passive elements” (3). Since pneuma is made of Air and Fire, that makes it as active as a mixture can be. Part of its active nature is to provide the cohesive force keeping together the passive elements. With Aristotle, we are to think of the continuum of the cosmos geometrically, where parts cohere simply by being spatially contiguous, that is, their extremities are in direct contact. [See Aristotle’s Physics, Book 6, section 1.] There is no force or activity involved there. But since the Stoics regard cohesion as involving the work of pneuma, that makes it a dynamic continuum rather than a geometrical one. However, Aristotle did go beyond the notion of continuity stemming from geometrical coherence when he conceived of unity as involving a binding agent, like a string binding together a bundle of sticks or glue binding together pieces of wood. [See Aristotle, Metaphysics, Book 5.] Aristotle also comes close to a dynamic conception of continuum when he speaks of things being continuous when their motion is one. [See Aristotle, Metaphysics, Books 5 and 8.] Nonetheless, the Stoics make the clear step of identifying continuity with an active sort of cohering.

The mixture of air and fire which was identified in Stoic physics with the pneuma thus became the active agent par excellence in their cosmos. Pneuma or one of its components was also defined by the collective “pneuma-like matter”, and the Stoics attributed to them the property of coherence in the twofold sense of being cohesive and making cohesive,25 whereas the passive elements (“hyle-like matter”) were denied any such faculty. Without the active interference of air or fire or the two mixed together, the passive elements would disintegrate as they themselves do not possess the “cohesive force”.26 Coherence thus appears here distinctly as a force, and the geometrical continuum of Aristotle is in this way transformed into a dynamic one. It should be mentioned, however, that Aristotle has occasionally used the term “cohesive” in a structural | sense; e.g. in his analysis of the concept of unity27: continuity is achieved by a binding agent and not by geometrical contact alone, as for instance a faggot which is made one by its string, and pieces of wood by glue. This is a static analogy, but immediately afterwards Aristotle comes very close to a dynamic conception when he calls a thing continuous “whose motion is essentially one and cannot be otherwise”. But the Stoics undoubtedly identified continuous with cohesive and thus completed the transformation of the geometrical concept into a physical one.

25. Galen, De multitud., 3 (Arnim, II, 439 and 440).

26. συνεκτικὴ δύναμις.


27. Arist., Metaph., 1015 b 36 f.



The physical property of pneuma is tension (tonos).

[...] the specifically physical property ascribed by the Stoics to the pneuma, or the “pneumalike matter” in general: tension (tonos). [...] since pneuma pervades the whole universe, the pneuma-like tonos makes the cosmos into a single cohesive unit34 and thus the pneuma becomes the first version of the aether with all the characteristic functions ascribed to it from the seventeenth century on.

34. Clemens Alex., Stromat., V, 8 (Arnim, II, 447).



Another physical feature of air and fire, which compose pneuma, is that they are gravitationally neutral, which means that neither rise nor fall to the extremes and thus can pervade all regions to serve as the universal binding agent.

The whole emphasis in this | text [on Zeno of Citium’s cosmology] is on the gravitationally neutral character of air and fire who both participate in the cosmic tendency towards the centre, and at the same time stretch from there to the extreme regions, and thus contribute to the communication between all the parts of the universe.

(6-7, bracketed insertion mine)





Sambursky, Samuel. 1973. Physics of the Stoics. Westport, Connecticut: Greenwood. [First published 1959, London: Routledge and Kagen Paul.]




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