Aristotle opens The Categories by distinguishing three modes of naming: things are named 'equivocally' when they share a name but differ in definition—as a real man and a painted figure both called 'animal'—and 'univocally' when both name and definition are identical, as with a man and an ox. A third class, 'derivatively,' covers terms like 'grammarian' from 'grammar.' This tripartite scheme immediately establishes the treatise's method: rigorous definitional analysis rather than empirical observation. The work then proceeds to classify 'things that are said' into categories, beginning with substance—that which is neither predicable of nor present in a subject—and moving through quantity, quality, relation, and others. The excerpts show a persistent concern with the logical behavior of terms, especially the distinction between being 'predicable of a subject' and being 'present in a subject,' a technical pair that structures much of the argument.

The Architecture of Predication

In Part 2, Aristotle introduces a fourfold classification of things based on two binary distinctions: whether a thing is predicable of a subject, and whether it is present in a subject. This yields four types: (1) predicable but not present (e.g., 'man' said of an individual man); (2) present but not predicable (e.g., a particular piece of grammatical knowledge in a mind); (3) both predicable and present (e.g., knowledge present in a mind and predicable of grammar); and (4) neither predicable nor present (e.g., an individual man or horse). This framework is not merely taxonomic; it underpins the entire categorial system. The individual substance—'that which is individual and has the character of a unit'—is never predicable, though it may be present in a subject. The careful wording reveals Aristotle's effort to avoid conflating logical predication with physical inherence, a distinction that later commentators would debate for centuries.

Qualities, Affections, and the Boundary of Permanence

The discussion of quality in Part 8 introduces a subtle criterion: a condition is a 'quality' if it is permanent or difficult to remove, but an 'affection' if it arises from easily reversible causes. Blushing from shame is not a quality but an affection, whereas a constitutional tendency to blush—if caused by 'certain permanent and lasting affections'—is a quality. Aristotle extends this to psychic states: inborn irascibility is a quality, but irritation provoked by a temporary vexation is not. This distinction reflects a deeper concern with what truly characterizes a thing's nature versus what is merely transient. The text also notes that rarity, density, roughness, and smoothness appear to indicate quality but actually refer to 'a certain relative position of the parts'—a reminder that surface-level attributions may mislead. The category of quality, then, is not a simple list but a domain where permanence, origin, and structure must be weighed.

Derivative Naming and the Limits of Language

Aristotle observes that most qualified things derive their name from the quality: 'whiteness' yields 'white,' 'grammar' yields 'grammatical.' But he acknowledges exceptions: a runner or boxer named from an inborn capacity has no corresponding quality name from which their title is derived. This admission reveals a gap between linguistic practice and logical structure. The treatise does not attempt to force all cases into a neat scheme; instead, it notes where the system has lacunae. Such moments—where the author points out that a quality 'has no name'—are instructive. They show that The Categories is not a closed system but an exploratory analysis that recognizes the limits of its own categories. The reader is left to consider whether these gaps are accidental omissions in Greek or signs of deeper conceptual boundaries.

Readers approaching The Categories should attend to the precise technical vocabulary Aristotle builds: 'equivocal,' 'univocal,' 'derivative,' 'predicable,' 'present in a subject.' Each term carries a specific logical weight, and the argument often turns on subtle distinctions between them. The work rewards slow reading, especially where Aristotle pauses to note exceptions or ambiguities. Rather than a finished doctrine, it offers a toolkit for analyzing how language maps onto reality—a toolkit that has shaped logic and metaphysics for over two millennia.