The truth of what is said by a T-sentence is compatible with the sentence used on the right-hand side being materially equivalent to but different in meaning from the sentence mentioned on the left
A sentence produced by a Tarskian truth theory; makes no explicit claims about meaning or content, but specifies truth conditions for sentences of the object language
materially equivalent(Russell's usage in his 1893 paper for Sidgwick)
but still not know the meaning of the sentence mentioned on the left-hand side of the T-sentence. The truth of what is said by this sentence, after all, is compatible with the sentence used on the right-hand side being materially equivalent to, but different in meaning from, the sentence mentioned on the left. This seems to indicate that knowing what is said by a truth theory of the relevant kind is not, after all, sufficient for understanding a language. (For replies to these criticisms, see Da