Verisimilitude

Verisimilitude (truthlikeness) is Popper’s attempt to make sense of the idea that one false theory can be closer to the truth than another. He defined it as a theory’s truth content minus its falsity content: a better theory says more true things and fewer false things about its subject. The motivation was real progress — Einstein superseding Newton — without claiming either theory is verified or probable. Popper’s 1960s formal definition was shown defective by David Miller and Pavel Tichý (1974): on it, no false theory can be more verisimilar than another, which collapses the comparison Popper wanted. Later programs tried to repair this, with no settled success.

Critical Fallibilism treats verisimilitude as one of a long list of terms — alongside corroboration, credence, plausibility, and probability — that try to grade how good an idea is. CF rejects all such gradations. Ideas get pass/fail evaluations: an idea is refuted (a known error stops it failing some goal) or it is not. To rank two rivals you must name a goal where one passes and the other fails, not assign each a degree of closeness on a single scale.

So CF reads verisimilitude as Popper reaching toward binary thinking — wanting comparative judgments of objective truth without justification — but importing a continuous metric that pulls back toward the scoring he otherwise opposed. CF keeps the fallibilist target of truth and the rejection of certainty while replacing the truthlikeness scale with multiple simple goal-relative verdicts.