In the “Refutation of Idealism” that he added to the second edition of the Critique of Pure Reason, Kant claims to refute what he calls problematic idealism. According to Kant, problematic idealism is a position, traceable to Descartes, which “declares the existence of objects in space outside us to be [ . . . ] doubtful and indemonstrable” (B 274). Against this position, Kant wants to prove “that even our inner experience, undoubted by Descartes, is possible only on the presupposition of outer experience” (B 275). Kant presents the following argument for this thesis: “(1) “I am conscious of my existence as determined in time” (B 275). / (2) “All time-determination presupposes something persistent in perception” (B 275). / (3) “This persisting thing, however, cannot be something in me, since my own existence in time can first be determined only through this persisting thing” (B 275). / (4) “Thus the perception of this persistent thing is possible only through a thing outside me” (B 275). / (5) “Consequently, the determination of my existence in time is possible only by means of the existence of actual things that I perceive outside me” (B 275).”