It would be impossible in a discussion of moderate length to touch upon all the points which have been raised in connexion with this problem; but some service will have been rendered if a few of the more important features of the question are pointed out and classified under the two heads just indicated, as certain or not certain. In any scientific enquiry, whether historical or experimental, this classification is a useful one, and very often leads to the enlargement of the class of certainties. When the group of certainties has been properly investigated, and when the various items have been placed in their proper relations to one another and to the whole of which they are only constituent parts, the result is likely to be a transfer of other items from the domain of what is only probable or possible to the domain of what is certain. At the outset it is necessary to place a word of caution as to what is meant, in a question of this kind, by _certainty_. There are no limits to scepticism, as the history of speculative philosophy has abundantly shown. It is possible to question one's own existence, and still more possible to question the irresistible evidence of one's senses or the irresistible conclusions of one's reason. _A fortiori_ it is possible to throw doubt upon any historical fact. We can, if we like, classify the assassinations of Julius Cæsar and of Cicero, and the genuineness of the Æneid and of the Epistles to the Corinthians, among things that are not certain. They cannot be demonstrated like a proposition in Euclid or an experiment in chemistry or physics. But a sceptical criticism of this kind makes history impossible; for it demands as a condition of certainty a kind of evidence, and an amount of evidence, which from the nature of the case is unattainable. Juries are directed by the courts to treat evidence as adequate, which they would be willing to recognize as such in matters of very serious moment to themselves. There is a certain amount of evidence which to a person of trained and well-balanced mind makes a thing "practically certain:" _i.e._, with this amount of evidence before him he would confidently act on the assumption that the thing was true. In the question before us there are four or five things which may with great reason be treated as practically certain.