This is the most recent discussion, on a great scale, of the theory of Certitude. But the question, far from being a new or modern speculation, is as old as Philosophy itself, and has been perpetually reproduced in every age of intellectual activity. Plato discusses it, chiefly in the Theaetetus, Sophist, and Parmenides; it was agitated by Pyrrho, Enesidemus, and Sextus Empiricus, with that peculiar subtlety which belonged to the mind of Greece; and in more recent times it has reappeared in the writings of Montaigne and Bayle, Huet and Pascal, Glanville, Hume, and Kant. Even during the middle age, the controversy between the Nominalists and Realists had an important bearing on this subject: so that from the whole history of Philosophy we derive the impression of its fundamental importance, an impression which is deepened and confirmed by the transcendent interest of the themes to which it has been applied. In our present argument, we are concerned with it only so far as it stands connected with the foundations of Theology, or as the right or wrong solution of the general question might affect the evidence for the Being and Perfections of God. We do not propose, therefore, to offer a full exposition of the philosophy of Certitude, still less to institute a detailed examination of the various theories which have been propounded respecting it. It will be sufficient for our purpose if we merely sketch a comprehensive outline of the subject, and select some of the more prominent points which have the most direct bearing on the grounds of our religious belief. Thus much may be accomplished by considering, _first_, the statement of the problem, and, _secondly_, the solution of it.