We discuss Aristotle's "Categories" as an answer to Plato's One-over-Many argument. For Plato, F-ness is something "over against" particular F things; to predicate "F" of these things is to assert that they all stand in a certain relation to F-ness. Aristotle answers that predication is classification; and there being a classification of a certain sort is a fact correlative with there being things classifiable in the way the classification in question would classify them.

It is not certain when or by whomandwere first technically distinguished asgenusandspecies. The distinction does not appear in Plato's extant writings, whereas Aristotle seems to take it for granted in theTopics, which is usually regarded as among his earliest treatises. In his dialogues Plato seems able to useinterchangeably to denote any group or division in a diairesis, including the group that is to be divided.