Full Idea
It is the categories that elevate mere perception into objectivity, into experience; but these concepts ...are conditioned by the given material. ...Hence the understanding, or cognition through categories, cannot become cognizant of things-in-themselves.
Gist of Idea
Categories create objective experience, but are too conditioned by things to actually grasp them
Source
Georg W.F.Hegel (Logic (Encyclopedia I) [1817], §43-4)
Book Reference
Hegel,Georg W.F.: 'The Hegel Reader', ed/tr. Houlgate,Stephen [Blackwell 1998], p.156
A Reaction
As one often fears with Hegel, this sounds like a deep insight, but is less persuasive when translated into simpler English (if I've got it right!). Being 'conditioned by the material' strikes me as just what is needed for good categories.