Tiberiu Popa (Butler University Indianapolis): Aristotle on microstructures and capacities

The capacities for change of what Aristotle takes to be uniform materials are essential to his explanations of various higher-level capacities (e.g., mental or temperamental dispositions, the functions of instrumental parts, specific capacities for the development of embryos etc.) and also to the ways in which we can manipulate organic and inorganic homoeomers.

A potentially illuminating aspect of Aristotle’s accounts of material properties that has not been explored as systematically as his treatment of dunameis is his reliance on structural characteristics that are imperceptibly small, but presumably inferable – if not with certainty, at least with a high degree of confidence. This may look at first sight rather counterintuitive, given that he excoriates various brands of atomism. Aristotle’s GC (I.10 and II.7) puts forth an account of uniform substances based on a concept of thorough combination (mixis) that is quite unlike, say, Democritus’ appeal to the combination and recombination of irreducibly small particles.

And yet, without contradicting himself, he also speaks quite liberally and with no apparent hesitation about invisible channels which render certain solids soluble, squeezable or combustible, about interlocking structures that explain viscosity, about undetectably small bubbles that account for certain dispositions of semen and olive oil, about earthy fibers in most kinds of blood, or apparently discrete earthy corpuscles in milk, and so on. Such causal factors are put to work in Generation of Animals, Parts of Animals, Meteorology etc. in addition to the fact that chemical combinations (especially of earth and water in various ratios, sometimes of air as well) can also causally explain a wide range of passive and resistive capacities.

While references to such microstructural features are rather numerous, they don’t constitute the object of a distinct inquiry in Aristotle. To see what he thinks about their explanatory role and about the confidence with which a natural philosopher can reasonably invoke them, we need to consider several passages that I find mutually relevant and that together offer a striking outline of his interest in microstructures. A close look at some of those passages is worthwhile for three reason:

  • It can help us better appreciate the place of those microstructures in his explanatory apparatus (in his ‘biochemistry’, in his biology and beyond).
  • It can invite some cautious but hopefully profitable reflection on the relevance of his attitude (that is, his epistemic optimism with respect to unobservable structural characteristics and their explanatory prowess regarding capacities) to recent and current debates in metaphysics, philosophy of science and philosophy of biology.
  • It can help us clarify key episodes in the reception of Aristotle’s science and natural philosophy. His interest in various types of microstructures captivated several major figures in the early modern history of alchemy and ‘chymistry’; they sometimes made him sound downright atomistic, while portraying Democritus as a proto-Aristotelian. I will not dwell, though, on this third aspect.

My main goal here is to capture Aristotle’s careful connections between microstructures and the dispositions which they are meant to explain partially and which, conversely, function as signs or indicators for both the existence of microstructures (e.g., poroi and penetrating corpuscles of water) and for some of their peculiarities (e.g., the diameters and arrangements of poroi). I will also pay attention to the way in which he expresses the asymmetrical relation of dependence between dispositional properties and structural features.

In the final section of my presentation, I would like to suggest that Aristotle’s use of microstructures in his explanations of sundry material dispositions raises questions that may be relevant (taking into account all the significant differences) to ongoing debates and can encourage some fresh reflection. In addition to the relation between dispositions and categorical properties and to the distinction between causation and grounding, I’m thinking especially about whether accounts of change in terms of mechanisms are compatible with discussions about dispositions and whether the two should even be regarded perhaps as mutually dependent.


This lecture was given on Fri, 2 July 2021, 10:50 (UK time) as part of the workshop Change and Changemakers in Ancient Philosophy. The workshop is a collaborative initiative of the Change and Changemakers Network (Siegen) together with the Mereology of Potentiality Project (Oxford).

Further note: It was brought to the attention of the organizers of the workshop »Change and Changemakers in Ancient Philosophy« that according to media reports the speaker of this lecture was arrested some months after the conference. The organizers had no knowledge of his alleged actions either at the time of the invitation or during the conference. This webpage will remain accessible as the speaker’s lecture has been accepted and held based on academic merit and bears no relation to the allegations against the speaker. It should be noted that the source of the information is not verifiable by the organizers.