Full Idea
Cartesian scepticism agonises over whether our beliefs are true or false, whereas Kantian scepticism agonises over how it is even possible for beliefs to be true or false.
Gist of Idea
Cartesian scepticism doubts what is true; Kantian scepticism doubts that it is sayable
Source
Tim Button (The Limits of Reason [2013], 07.2)
Book Reference
Button,Tim: 'The Limits of Realism' [OUP 2013], p.56
A Reaction
Kant's question is, roughly, 'how can our thoughts succeed in being about the world?' Kantian scepticism is the more drastic, and looks vulnerable to a turning of the tables, but asking how Kantian worries can even be expressed.
Related Idea
Idea 577 Democritus says there is either no truth, or it is concealed from us [Democritus, by Aristotle]