Full Idea
You can't treat understanding a sentence as knowing its truth conditions, because it then becomes unintelligible what that knowledge in turn consists in.
Gist of Idea
Truth conditions can't explain understanding a sentence, because that in turn needs explanation
Source
Hilary Putnam (Meaning and the Moral Sciences [1978], Pt Four)
Book Reference
Putnam,Hilary: 'Meaning and the Moral Sciences' [RKP 1981], p.129
A Reaction
The implication, I take it, is circularity; how can you specify truth conditions if you don't understand sentences? Putnam here agrees with Dummett that verification must be involved. Something has to be taken as axiomatic in all this.