What Makes One Idea Better Than Another?

Popper says to prefer ideas that are better corroborated, more truthlike. I wrote about this recently, pasting it here:

Corroboration was meant to help us form rational preferences between ideas. From The Logic of Scientific Discovery (pp. 281-282):

We can sometimes rationally justify the preference for a theory in the light of its corroboration, that is, of the present state of the critical discussion of the competing theories, which are critically discussed and compared from the point of view of assessing their nearness to the truth (verisimilitude). The current state of this discussion may, in principle, be reported in the form of their degrees of corroboration.

Specifically, corroboration helps you form a rational preference between two theories that have both been shown to be false while there are no known alternatives. From Conjectures and Refutations (p. 318):

… even after t2 has been refuted in its turn, we can still say that it is better than t1, for although both have been shown to be false, the fact that t2 has withstood tests which t1 did not pass may be a good indication that the falsity-content of t1 exceeds that of t2 while its truth-content does not. Thus we may still give preference to t2, even after its falsification, because we have reason to think that it agrees better with the facts than did t1.

That “t2 has withstood tests which t1 did not pass” means t2 is better corroborated than t1.