Full Idea
Schopenhauer dispenses with Kant's a priori categories, since all interrelations between representations are given through the principle of sufficient reason.
Gist of Idea
No need for a priori categories, since sufficient reason shows the interrelations
Source
report of Arthur Schopenhauer (Fourfold Root of Princ of Sufficient Reason [1813]) by Peter B. Lewis - Schopenhauer 3
Book Reference
Lewis, Peter B.: 'Schopenhauer' [Reaktion Books 2012], p.73
A Reaction
I'm not sure how Schopenhauer manages this move. Is it the stoic idea that reality has a logical structure, which can be inferred? Sounds good to me. Further investigation required.