Verisimilitude

I will now give an idea of what I mean by likely or verisimilar. [—] I call that theory likely which is not yet proved but is supported by such evidence, that if the rest of the conceivably possible evidence should turn out upon examination to be of a similar character, the theory would be conclusively proved. Strictly speaking, matters of fact never can be demonstrably proved, since it will always remain conceivable that there should be some mistake about it.

The names which I would propose for general adoption for the three different kinds of acceptability of propositions are

The last alone seems to be capable of a certain degree of exactitude or measurement

[—]

By verisimilitude I mean that kind of recommendation of a proposition which consists in evidence which is insufficient because there is not enough of it, but which will amount to proof if that evidence which is not yet examined continues to be of the same virtue as that already examined, or if the evidence not at hand and that never will be complete, should be like that which is at hand. All determinations of probability ultimately rest on such verisimilitudes. I mean that if we throw a die 216 times in order to ascertain whether the probability of its turning up a six at any one throw differs decidedly from 1/6 or not, our conclusion is an affair not of probability as Laplace would have it, by assuming that the antecedent probabilities of the different values of the probability are equal, but is a verisimilitude or as we say a “likelihood.”