In this task, you are given a question and a context passage. You have to answer the question based on the given passage.

What did Kant study?, Context: The 2nd edition (1787) contained a Refutation of Idealism to distinguish his transcendental idealism from Descartes's Sceptical Idealism and Berkeley's anti-realist strain of Subjective Idealism. The section Paralogisms of Pure Reason is an implicit critique of Descartes' idealism. Kant says that it is not possible to infer the 'I' as an object (Descartes' cogito ergo sum) purely from "the spontaneity of thought". Kant focused on ideas drawn from British philosophers such as Locke, Berkeley and Hume but distinguished his transcendental or critical idealism from previous varieties;
transcendental idealism