Categories of the understanding
immanuel-kant's twelve pure concepts that the understanding brings to experience, from the Analytic of Concepts in critique-of-pure-reason. They are the understanding's contribution in the two-stems picture: intuition supplies content, the categories supply the form in which objects can be thought. Written from the English Wikipedia article (T2). Not to be confused with the mathematical "category" of category-theory, or with the "category" of the market-intelligence pages; the Kantian sense is an old philosophical one.
The twelve
Four headings, three each:
- Quantity: unity, plurality, totality.
- Quality: reality, negation, limitation.
- Relation: inherence and subsistence; causality and dependence; community.
- Modality: possibility and impossibility; existence and non-existence; necessity and contingency.
Where they come from
Per Wikipedia, Kant derives them from twelve logical forms of judgment in the Metaphysical Deduction. The hypothetical judgment ("if A, then B"), for example, yields causality. The Transcendental Deduction then argues that they are conditions of any experience of objects, a step sep-transcendental-arguments discusses in detail and where it names the twelve categories.
Their limit is the same as the thing-in-itself problem: they apply to appearances, which is why causality used of a thing-in-itself looks illegitimate.
Related
critique-of-pure-reason · immanuel-kant · sep-transcendental-arguments · thing-in-itself · antinomies-of-pure-reason