Aristotle on Primary and Secondary Substance in the Categories

Aristotle lays out his understanding of the difference between primary and secondary substance in the Categories. In this post, I will explain both Aristotle’s understanding of substance in general as he lays it out in the Categories and his understanding of the difference between primary and secondary substance in particular.

In the Categories, Aristotle is primarily concerned with the way in which we speak about reality and the things in it and with how the way we so speak reveals the nature of reality. In particular, Aristotle is concerned with the way in which we make predications, which combine a subject and a predicate with a copula, resulting in a statement that is either true or false. For example, consider the statement ‘Socrates is pale.’ ‘Socrates’ is the subject of the predication, ‘pale’ is the predicate, and ‘is’ is the copula connecting them. Further, we say that ‘pale’ is predicated of ‘Socrates.’ The subjects and predicates always correspond to beings belonging to various possible categories, of which there are ten: substance, quantity, quality, relative, where, when, being in a position, having, acting on, and being affected.

For Aristotle, there is a fourfold division of the relationship between subjects and predicates in statements. This division is given as follows:

1. Things said of and in.
2. Things said of and not in.
3. Things not said of but (and) in.
4. Things not said of and not in.

Consider the statement ‘S is P.’ We say that P is said of S if both the name of P and the account of P apply to S. The name of P is simply ‘P’, that term which refers to P. The account of P is its essence, which is captured in a definition. If the essence of P applies to S, then everything true of P will also be true of S. For example, consider the statement ‘Socrates is a man.’ In this statement, man is said of Socrates, for both the name and account of man apply to Socrates. The name applies because we call Socrates a man. Further, the account applies because Socrates is a man, that is to say, the essence of man is of his very essence so that whatever is true of man will also be true of Socrates.

We say that P is in S if P belongs to S, not as a material part (though perhaps as a metaphysical constituent), and P cannot exist separately from S. Consider, for example, the statement that ‘Socrates is pale.’ In this case, pale is said to be in Socrates since it belongs to him and cannot exist separately from him. By contrast, in the statement ‘Socrates is a man,’ man is not in Socrates as it doesn’t belong to Socrates. Socrates does not have man; rather, Socrates is a man. Aristotle tells us that in most cases, if P is in S, then neither the name nor the account of P will apply to S. In some cases, however, the name will apply, but in no case will the account apply. For example, consider the statement ‘The table is white.’ In this case, white is in the table as it belongs to it. Further, the name ‘white’ applies to the table since we call the table white. However, the account of white does not apply to the table, i.e., the essence of white does not apply to the table. This is because, for instance, while it is true of white that it is the lightest color, it is not true of the table that it is the lightest color.

With these explanations in place, Aristotle tells us that primary substances are neither said of nor in anything and that secondary substances are said of primary substances and other secondary substances (and nothing else in the other categories) and are not in anything. Substance in general, then, is what is neither said of nor in anything in the other categories, and the difference between primary and secondary substance in particular is that primary substance is neither said of nor in anything at all, while secondary substance is said of but is not in other substances. In this way, then, substance in general is not predicated of any of the other categories, secondary substance is predicated of substance (as something said of but not in), and primary substance is not predicated of anything.

Aristotle does not stop here, however. He additionally tells us that primary substances are concrete individuals like Socrates and Callias and that secondary substances are universal kinds—genus and species—that the primary substances fall under. Aristotle explains that a primary substance is a this, while a secondary substance is not a this but is rather a kind. A secondary substance tells us what kind of substance a primary substance is. For example, Socrates and Callias both fall under the species man, which in turn falls under the broader genus animal. Further, Aristotle tells us that secondary substances cannot exist apart from primary substances. For instance, if there were no particular men, then there would be no species man. In this way, secondary substances ontologically depend on primary substances for their being. Moreover, this is true of everything in the rest of the categories. Everything is either a primary substance or ontologically depends on a primary substance. This follows from the fact that primary substances are the ultimate subjects of predication and the fact that, for Aristotle, if P is predicated of S, then P ontologically depends on S.

There are two components to what is meant by ‘ultimate.’ First, and as has already been said, primary substances are not predicated of anything. Second, every predication is ultimately predicated of a primary substance. Aristotle tells us that whatever is predicated of what is predicated of a thing is also predicated of that thing (either as something said of that thing or as something in that thing). For example, consider the statements that ‘Socrates is a man’ and that ‘Man is an animal.’ In this case, animal is predicated of man, but it is ultimately predicated of Socrates, and we can thereby infer the statement that ‘Socrates is an animal.’ Socrates is the stopping point for this chain of predications, and, in general, a primary substance is always the stopping point for a chain of predications. In this way, primary substances do not ontologically depend on anything, and everything else—including secondary substances—ontologically depend on primary substances.

A final feature that distinguishes primary substances from everything else is that primary substances can—as numerically one and the same thing—receive contraries, i.e., contrary attributes (though not, of course, at the same time). Aristotle thinks that this is what is “most distinctive” of primary substances. For example, Socrates can be pale at one time and tan at another, while remaining numerically one and the same thing. Overall, then, it is clear what substance is in general and what the difference between primary and secondary substance is in particular for Aristotle in the Categories.

There is a significant interpretational puzzle as to how Aristotle's account of primary versus secondary substance in the Categories relates to his account of substance in the Metaphysics. I shall leave a discussion of this for a future post.