Full Idea
There is no prospect whatever of giving the sense of a logical constant without using that very constant, and much else besides, in the metalinguistic principle that specifies that sense.
Gist of Idea
In specifying a logical constant, use of that constant is quite unavoidable
Source
Ian Rumfitt (The Boundary Stones of Thought [2015], 1.1)
Book Reference
Rumfitt,Ian: 'The Boundary Stones of Thought' [OUP 2015], p.9