Full Idea
For Kant, concepts should be thought of as rules for the combination of representations.
Gist of Idea
Concepts are rules for combining representations
Source
report of Immanuel Kant (Critique of Pure Reason [1781]) by Terry Pinkard - German Philosophy 1760-1860 01
Book Reference
Pinkard,Terry: 'German Philosophy 1760-1860' [CUP 2002], p.26
A Reaction
Kant seems to have thought that they are rules we decree for ourselves (like the categorical imperative). So think of private languages, and you get Hegel's much more social view of concepts (I think).