Full Idea
If a theory is a better approximation to the truth, then it is likely that it will have greater predictive power.
Gist of Idea
More truthful theories have greater predictive power
Source
W.H. Newton-Smith (The Rationality of Science [1981], VIII.8)
Book Reference
Newton-Smith,W.H.: 'The Rationality of Science' [RKP 1981], p.197