We have no reason to regard the new theory as better than the old theory — to believe that it is nearer to the truth — until we have derived from the new theory new predictions which were unobtainable from the old theory (the phases of Venus.) and until we have found that these new predictions were successful.

Conjectures and Refutations: The Growth of Scientific Knowledge, Chapter 10 (p. 246), Harper & Row, Publishers. 1963