Full Idea
A theory of truth for a language shows how the truth conditions of any sentence depend on the structure of that sentence. The theory will say, for each element of structure, what its contribution is.
Gist of Idea
Truth in a language is explained by how the structural elements of a sentence contribute to its truth conditions
Source
Gilbert Harman (Thought [1973], 5.1)
Book Reference
Harman,Gilbert: 'Thought' [Princeton 1977], p.71
A Reaction
This just seems to push the problem of truth back a stage, as you need to know where the truth is to be found in the elements from which the structure is built.