Certainty, on the other hand, attaches in the highest degree to certain beliefs that, in the nature of the case, are 'incapable of proof,' that is, of being tested. No belief is more certain for all men than the belief that they will all die, though the event, posited as future, cannot as such be 'tested.' In this case, the connotation of the word 'proof,' nevertheless, is by common consent transferred to the concept of mortality: the invariable dying of all previous men is allowed to be 'proof,' or decisive evidence, that all living men will die to the last generation. In regard to some other certainties, the concept of 'proof' is wholly irrelevant. You cannot 'prove' that you feel a pain, though it is one of the most certain of all facts for you while it lasts. If, then, any general scientific or other belief be shown to be 'incapable of proof,' in this merely negative sense (as distinguished from 'capable of disproof'), that is no argument against it for any practical or philosophic purpose. Such a belief is that in the 'uniformity of nature,' which is held by the same tenure as that in the mortality of all men. It cannot be 'proved,' either as to the past or the future, in the sense of being tested, save as regards past particulars, which are necessarily a small selection from the totality of phenomena. For the future, in the terms of the case, there can be no proof. Yet no man has any more doubt as to the rising of the sun to-morrow than as to his own ultimate death. Concerning this we are quite certain, which we cannot be as to many things reasonably held to have been 'proved.' Such and such are our 'certainties.' What, then, is Mr. Balfour's case against men of 'science,' and those whom he calls 'the Freethinkers'? It may be put under three heads.