Full Idea
Kant says that a priori knowledge is limited to objects of possible experience, and this is the core thesis of his distinctive doctrine of transcendental idealism.
Gist of Idea
A priori knowledge is limited to objects of possible experience
Source
report of Immanuel Kant (Critique of Pure Reason [1781]) by Nicholas Jolley - Leibniz Ch.8
Book Reference
Jolley,Nicholas: 'Leibniz' [Routledge 2005], p.213
A Reaction
Some people would even challenge this bold claim for a priori knowledge, but this idea shows why Kant was said to have put an end to old fashioned speculative metaphysics. For Kant, a priori knowledge seems to be something like introspection.