What is Kant's opinon on Descartes's Cogito Ergo Sum

Question

Does Kant agree with Descartes that because he thinks, he can know for certain that he is a thinking thing. Or does he think differently because substance is one of his apriori categories and so he may only appear to be a thinking thing?

Answer 1

Kant does not agree with Descartes that I can deduce anything about the nature of my being from my act of thought. Descartes famously refers to any conscious being as a res cogitates or thinking thing. For Kant, by contrast, the "I think" or cogito "must be able to accompany all my representations". This seems to mean that I am able to reflect on any of my mental acts. But this permanent possibility of mental reflection tells me nothing positive about the nature of my being. This falls in line with Kant's ontological agnosticism more generally. His "transcendental idealism" posits that human understanding can only know how things as they appear and never - as traditional metaphysics including Descartes contends - come to know things as they are in themselves. Substance is indeed one of Kant's categories or basic concepts of the understanding. These concepts are considered by Kant to be that through which all human understanding comes to know things as they are given, in the first instance, to the mind through the senses. Kant rules out the possibility of what he calls a "rational psychology", by which he means direct knowledge of the mind or psyche by means of reason alone.