Full Idea
Only from the understanding can pure concepts arise, and reason cannot generate any concept at all, but can only free a concept of the understanding from the unavoidable limitations of possible experience, and extend it beyond empirical boundaries.
Gist of Idea
Reason generates no concepts, but frees them from their link to experience in the understanding
Source
Immanuel Kant (Critique of Pure Reason [1781], B435/A409)
Book Reference
Kant,Immanuel: 'Critique of Pure Reason', ed/tr. Guyer,P /Wood,A W [CUO 1998], p.460
A Reaction
Presumably Descartes' 'natural light' should cover the understanding as much as the reason. This quotation brings out the empirical aspect of Kant's thought. It suggests that analysis is the main function of reason.