I take as my text propostion 4.0312 of the Tractatus:

The possibility of propositions is based on the principle that objects have signs as their representatives.

My fundamental idea is that the ‘logical constants’ are not representatives; that there can be no representatives of the logic of facts.

Practically the same words occur (with two additional sentences) in Wittgenstein's Notebook for 25 December 1914, where Miss Anscombe translates them:

The possibility of the proposition is, of course, founded on the principle of signs as going proxy for objects.

Thus in the proposition something has something else as its proxy. But there is also the common cement.

My fundamental thought is that the logical constants are not proxies. That the logic of the fact cannot have anything as its proxy.