Full Idea
Why should I think of myself as a legislator and at the same time a citizen of a republic governed by some notional laws?
Gist of Idea
Why should I think of myself as both the legislator and the citizen who follows the laws?
Source
Bernard Williams (Ethics and the Limits of Philosophy [1985], Ch. 4)
Book Reference
Williams,Bernard: 'Ethics and the Limits of Philosophy' [Fontana 1985], p.63
A Reaction
Kant's answer is supposed to be 'because you are rational, and hence must want consistency'. If we were all rational, Kant would be right.