6 Jan 2017

Uexküll (3.4) Theoretical Biology, “The Mark-Signs”, summary


by Corry Shores


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[The following is summary. All boldface and bracketed commentary is my own. Proofreading is incomplete, so please forgive my typos. Page citations refer to the 1928 German edition first and to the 1926 English edition second.]





Summary of


Jakob von Uexküll


Theoretical Biology

[Theoretische Biologie]


Ch.3 The Content-Qualities

[Die Inhaltsqualitäten]


3.4 The Mark-Signs

[Die Merkzeichen]




Brief summary:

Each threshold in our awareness of variation presents a “mark-sign”. The ability to discern mark signs varies for the person or creature, depending on their level of sensitivity to that sort of qualitative variation. There are two kinds of mark-signs. {1} Qualitative  mark-signs: these distinguish qualitatively-different things, and they are represented by angles in our diagrams. {2} Intensive mark-signs: these are found along a continuum of variation; they are determined by thresholds of variation-awareness; and they are represented in our diagrams by the lines between the qualitative mark-sign angles.







[A “mark-sign” corresponds to a threshold in our attention. So a mark-sign is found at each of the smallest discernible objective changes in a stimulus. (It is an “alteration in the content that is just perceptible to the attention”.)]


[In the prior section we discussed a method of determining thresholds, based on Weber’s technique. The idea is that a continuously varying objective intensity in a stimulus is perceived in steps. The objective stimulus can increase continuously without our sensing it, but when it crosses a certain threshold in our awareness, we notice a change. We can think of these thresholds as moments when our attention changes or “turns”. Uexküll will now define his notion of the mark-sign in terms of these thresholds where our attention changes.] “By employing the method of determination of threshold, and developing the same principle, we arrive at the concept of the mark-sign” (65 / 76). [Uexküll describes a method for finding the thresholds or mark-signs in a color continuum. It seems the procedure finds the smallest objective variations that we can discern as distinguishable. Apparently, we keep magnifying the constituent parts of the continuum until we find a part where we are unable to discern a difference. The number of all the smallest discernible parts is the number of mark-signs in the continuum.]

We divide up the whole colour-band between two turning-points into tiny segments lying alongside one another, and make them so small that at least two adjacent parts, considered by themselves, are indistinguishable by the eye. Now let us magnify the individual parts until every two adjacent ones become just distinguishable from one another. Then the number of individual parts gives the number of mark-signs that the colour-band holds for us. Interpreted in this way, the mark-sign means the alteration in the content that is just perceptible to the attention.

(65-66 / 76)




[The capacitiy to discern mark-signs varies with abilities and handicaps, like between a trained musician and a tone-deaf person.]


Certain people are more sensitive to color variations, and thus they experience more mark-signs in the same color continuum. “The number of mark-signs for colour increases with the skill of the individual observer in distinguishing colours; it gives us a clue to the amount of colour in his appearance-world [Erscheinungswelt]” (66 / 76, bracketed insertion mine). Color-blind people have fewer color mark-signs. While those with normal sight can think of the color-blind person’s appearance world by subtracting colors, the color-blind person is unable to imagine what it is like to have those color mark-signs. The same holds for those with tone-deafness (66 / 76).



[There are two kinds of mark-signs: {1} qualitative  mark-signs, which distinguish qualitatively-different things and which are represented by angles in our diagrams, and {2} intensive mark-signs, which are found along a continuum, are determined by thresholds of variation-awareness, and are represented in our diagrams by the lines between the qualitative mark-sign angles.]


Uexküll then distinguishes two sorts of mark-signs: {1} mark-signs of qualitative difference, and {2} mark-signs of intensive difference. Qualitative differences are always ones involving definite qualities, and we represented them using angles in our spatial diagrams. But other less qualitatively definite qualities appear as intensive variations between definite qualities. They are distinguished by the thresholds.  [Recall the color example from section 3.2.


Here we see the two different sorts of mark-signs. Red, yellow, green, and blue are qualitative mark-signs, and the variations between them contain a series of intensive mark-signs.] When assessing intensive mark-signs, it is arbitrary where we start and which direction we go (66 / 76-77).






Works cited (in this order):


Uexküll, Jakob von. 1928. Theoretische Biologie, 2. gänzlich neu bearbeitete Auflage. Berlin: Springer.


Uexküll, Jakob von. 1926. Theoretical Biology. Translated by Doris Livingston MacKinnon. London: Kegan Paul, Trench, Trubner & Co. / New York: Harcourt, Brace & Company. PDF available at:





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