How is it possible that probability statements—which are not falsifiable—can be used as falsifiable statements? (The fact that they can be so used is not in doubt: the physicist knows well enough when to regard a probability assumption as falsified.) This question, we find, has two aspects. On the one hand, we must make the possibility of using probability statements understandable in terms of their logical form. On the other hand, we must analyse the rules governing their use as falsifiable statements.
According to section 66, accepted basic statements may agree more or less well with some proposed probability estimate; they may represent better, or less well, a typical segment of a probability sequence. This provides the opportunity for the application of some kind of methodological rule; a rule, for instance, which might demand that the agreement between basic statements and the probability estimate should conform to some minimum standard. Thus the rule might draw some arbitrary line and decree that only reasonably representative segments (or reasonably ‘fair samples’) are ‘permitted’, while atypical or non-representative segments are ‘forbidden’.