The Categories (Greek Κατηγορίαι Katēgoriai; Latin Categoriae) is a text from Aristotle's Organon that enumerates all the possible kinds of things that can be the subject or the predicate of a proposition. They are "perhaps the single most heavily discussed of all Aristotelian notions".[1] The work is brief enough to be divided, not into books as is usual with Aristotle's works, but into fifteen chapters.

The Categories places every object of human apprehension under one of ten categories (known to medieval writers as the Latin term praedicamenta). Aristotle intended them to enumerate everything that can be expressed without composition or structure, thus anything that can be either the subject or the predicate of a proposition.

The text begins with an explication of what is meant by Aristotle "synonymous," or univocal words, what is meant by "homonymous," or equivocal words, and what is meant by "paronymous," or denominative (sometimes translated "derivative") words.

It then divides forms of speech as being:

Either simple, without composition or structure, such as "man," "horse," "fights," etc.
Or having composition and structure, such as "a man argued," "the horse runs," etc.
Only composite forms of speech can be true or false.

Next, he distinguishes between what is said "of" a subject and what is "in" a subject. What is said "of" a subject describes the kind of thing that it is as a whole, answering the question "what is it?" What is said to be "in" a subject is a predicate that does not describe it as a whole but cannot exist without the subject, such as the shape of something. The latter has come to be known as inherence.