Full Idea
Truth is one species of good, and not, as is usually supposed, a category distinct from good, and co-ordinate with it. The true is whatever proves itself to be good in the way of belief, and good, too, for definite, assignable reasons.
Gist of Idea
Truth is a species of good, being whatever proves itself good in the way of belief
Source
William James (Pragmatism - eight lectures [1907], Lec 2)
Book Reference
James,William: 'Pragmatism - eight lectures' [Dover 1995], p.30
A Reaction
The trouble is that false optimism can often often be what is 'good in the way of belief'. That said, I think quite a good way to specify 'truth' is 'success in belief', but I mean intrinsically successful, not pragmatically successful.