Aristotle’s Categories (1b25) states that incomplex expressions signify either Substance (e. g., Man) or Quantity (e. g., Two cubits long) or Quality (e. g., White) or Relation (e. g., Double) or Where (e. g., In the market place) or When (e. g., Yesterday) or Position (e. g., Lying) or State (e. g., Shod) or Action (e. g., To cut) or Affection (e. g., To be cut). These are the ten Aristotelian categories. The non-Substance categories are known as Accidents.
Among substances, Aristotle distinguishes primary substances (e. g., the individual man) as being neither said of a subject nor present in a subject (2b11). Two types of predication are thus distinguished (2a19). What is ‘‘said of’’ a subject (as Animal is said of Man) is predicated, both in name and definition, of the subject. What is ‘‘present in’’ a subject (as Grammatical knowledge is present in Man) may be predicated in name, but not in Definition, of the subject; it is not part of the subject and cannot exist apart from it (1a20).
According to the Categories, there are individual accidents as well as individual substances. Everything other than primary substance is either said of or present in a primary substance. Thus, it is sensible individuals, such as this man or this horse, which are substance in the truest and primary and most definite sense of the word - a claim that is diametrically opposed to Plato’s Theory of Forms, which states that intelligible Forms that are most truly substances.
The Categories mentions features peculiar to some of the categories, whereby they can be distinguished from other categories. It is common to all substances, and also to the differentiae whereby one species is distinguished from another, that they are not present in any subject (3a7). It is common to all substances and also peculiar to them that, while remaining numerically identical, they can receive contrary qualities through a process of change (4a10).
What is distinctive of quantity is that subjects can be equal or unequal to one another in respect of quantity (6a26). (But equality and inequality themselves are relatives.) What is distinctive of quality is that subjects can be similar or dissimilar to one another in respect of quality (11a15). (But similarity and dissimilarity themselves are relatives.)
Items in the category of relation are not relations in the modern sense, that is, many-place properties. A relation, like mastery, inheres in a single subject (a master), which stands toward an object (a slave). Every relative has a correlative, as Slave is correlative with Master. It seems to be a peculiarity of relatives that correlatives are simultaneous by nature: when one man becomes a master, another becomes a slave and when one becomes a slave, another becomes a master (7b15). (Aristotle discusses knowledge and the knowable as a possible counterexample to this claim.)
World History
