Full Idea
Kant claimed that things-in-themselves caused our sensations; but causality was a transcendental condition of experience, not a property of things-in-themselves, so the great Kant had contradicted himself.
Gist of Idea
Kant says things-in-themselves cause sensations, but then makes causation transcendental!
Source
report of Henry of Ghent (Quodlibeta [1284], Supplement) by Terry Pinkard - German Philosophy 1760-1860 04
Book Reference
Pinkard,Terry: 'German Philosophy 1760-1860' [CUP 2002], p.95
A Reaction
This early objection by the conservative Jacobi (who disliked Enlightenment rational religion) is the key to the dispute over whether Kant is an idealist. Kant denied being an idealist, but how can he be, if this idea is correct?