Hypokeimenon versus Substance

There is a curious lacuna in scholarship on Aristotle’s logic and metaphysics, in that few authors investigate Aristotle’s notion of ὑποκείμενον, or subject, in its own right, even by confining this investigation to his logical works. Though they tend to agree that it is offered as a criterion for substancehood in Categories, discussion of what it is to be a ὑποκείμενον is generally offered only in passing. There is a reason for this: Substance seems the more compelling topic, since it is about this that Aristotle is in a disagreement with Plato, and it is in the interest of this disagreement that Aristotle introduces the notion of ὑποκείμενον. But if being a ὑποκείμενον is so key to Aristotle’s exposition of his anti-Platonic view of substance, at least in his logical works, to the extent that we do not understand being a ὑποκείμενον we cannot understand what Aristotle is trying to tell us about what it is to be an οὐσία, or substance.

In Categories Aristotle gives neither a full exposition of what it is to be a substance nor, I shall argue, of what it is to be a subject. That Aristotle does not give a full exposition of what it is to be a substance in Categories is well known. Loux, for example, argues that in Categories οὐσία is taken as an “antecedently understood term,” ¹ such that Aristotle cannot merely stipulate the meaning but is participating in a debate in which the stipulated meaning of οὐσία is already established. In general, to be a substance for Aristotle or Plato is to be the sort of thing that is such that everything else in one’s ontology exists by depending on or being in some way related to a substance; it is what grounds everything else in one’s ontology. Alan Code ² and Russell Dancy ³ similarly point out that though Aristotle and Plato disagree about what it is to be a substance and which things are substances, they are still arguing about how to fill out a term of art on whose general use they agree. A theory of substance is what is needed, one that will give criteria for being a substance and finally help to determine which things are, in fact, substances.⁴

There is not a similar background for Aristotle’s use of the term ὑποκείμενον; it isn’t a term we find used in the same way among his predecessors, at least not in the way that Aristotle seems to use it in On Interpretation (henceforth, DI) and Categories.⁵ It is a term whose use, like the use of ἐντελεχεία (actuality), is developed and stipulated by him. Consequently, we might expect him to try to explain what is meant by it at some point. In Categories he gives some discussion of the framework in which it appears, detailing some of the rules of the predication relations it underlies. Yet he provides no criteria for being a ὑποκείμενον; he only asserts that some things are, and some things are not, subjects in the relevant sense, whatever this sense is. We can, therefore, glean something of what he means by it in Categories, but because the focus there is on which things are subjects, it is easy to be misled into assuming that all and only substances are ὑποκείμενα. If this is right, it is tempting to think that we need not say too much about what it is to be a ὑποκείμενον, for we can straightforwardly infer from what we know about substance what it is to be a ὑποκείμενον, so that the discussion of ὑποκείμενον receives short shrift.⁶

In this essay, in the first section I argue that in Categories being a ὑποκείμενον is not presented as the criterion for being a substance, for it is not the case that all and only substances are subjects. Since being a ὑποκείμενον is nevertheless clearly important to Aristotle’s characterization of substance in that work, the question of what Aristotle means by ὑποκείμενον is more pressing. To find out more about what it is to be ὑποκείμενον we must turn to a discussion of accidental (συμβεβηκός) and unqualified (ἁπλῶς) predication in Posterior Analytics 1.22, ⁷ one...