Will, Doubt, Practical Reason

Kant's 'I think', meaning 'I synthesize', is the inverse of Descartes' 'I think', meaning the dissociative 'I doubt'. On the other hand, his 'I reason', meaning 'I detach myself from an intention', parallels Descartes' 'I detach myself from a perception'. These, more precisely, are based on the possibility of doing otherwise, and of perceiving otherwise, respectively. So, while Kant shows more explicitly than does Descartes that Doubting is an expression of Will, Descartes' accepts the validity of his principle as self-evident, i. e. he adopts it as a method without either defending its possibility, or casting it as an objective rational law, as Kant does.