It seems to me, then, that we very often have true ideas which we cannot verify; true ideas, which, in all probability, no man ever will be able to verify. And, so far, I have given only comparatively trivial instances. But it is plain that, in the same sense, historians are very frequently occupied with true ideas, which it is doubtful whether they can verify. One historian thinks that a certain event took place, and another that it did not; and both may admit that they cannot verify their idea. Subsequent historians may, no doubt, sometimes be able to verify one or the other. New evidence may be discovered or men may learn to make a better use of evidence already in existence. But is it certain that this will _always_ happen? Is it certain that _every_ question, about which historians have doubted, will some day be able to be settled by verification of one or the other hypothesis? Surely the probability is that in the case of an immense number of events, with regard to which we should like to know whether they happened or not, it never will be possible for any man to verify either the one hypothesis or the other. Yet it may be certain that either the events in question did happen or did not. Here, therefore, again, we have a large number of ideas--cases where many men doubt whether a thing did happen or did not, and have therefore the idea both of its having happened and of its not having happened--with regard to which it is certain that half of them are true, but where it seems highly doubtful whether any single one of them will ever be able to be verified. No doubt it is just possible that men will some day be able to verify every one of them. But surely it is very doubtful whether they will. And the theory against which I am protesting is the positive assertion that we _can_ verify all our true ideas--that some one some day certainly will be able to verify every one of them. This theory, I urge, has all probability against it.