In the first paper of this series, which was devoted to the examination of the third proposition as announced by Mr. Buckle and substantially affirmed by Professor Draper, together with the consideration of the fundamental Law of Human Progress, the error into which both of these distinguished writers had fallen in regard to the relative influence of moral and intellectual truths, was pointed out; as also the misconception under which they rested concerning the Law of Human Development. This misconception, it was then shown, arose from an incorrect understanding of the essential character of the Law itself, and could be traced, basically, to the same source whence sprang their mistake in reference to the comparative power of moral and mental forces. It is to a misapprehension, analogous to that which brought him into error concerning these two important points, that the radical defect of Mr. Buckle's first and fourth propositions is to be traced, as will be hereafter exhibited. The complete and exhaustive consideration of the second proposition demands a range of Metaphysical examination which cannot be entered upon at this time. For our present purposes it may be dismissed with the following remarks: That before men begin the investigation of any subject _deliberately_, _reflectively_, and with a _fixed_ and _intelligent_ purpose of ascertaining the truth concerning it, there must arise some feeling of doubt in their minds in relation to the given subject or to some details of it, is certainly true, and needed no array of evidence to prove it; but that prior to such _conscious_ and _intentional_ effort at exploration, there exists an _unconscious_ or _automatic_ action in the mind, an instinctual and passive kind of thinking, a vague floating of ideas _into_ the mental faculties, rather than an apprehension of them by an active and deliberate _tension_ of the intellect, and that it is through this kind of _intuitive investigation_ that the 'spirit of scepticism' primarily arises, is equally true; though not, perhaps, at the first blush, so apparent. In this sense, the statement of Mr. Buckle is simply one half of a truism, the other half of which, not enunciated by him, is equally correct. Whether the spirit of scepticism--which then undoubtedly aids in the investigation--_is afterward aided or fostered by it_, depends upon the nature of the question investigated. If this be one which has hitherto been considered as established upon a basis that was in every respect right, and if errors are revealed in the process of the examination, then, indeed, the spirit of scepticism is strengthened. But if, on the contrary, the investigation be in reference to a range of thought which rests upon a basis that is, in all ways, sound--concerning Mathematical truths, for instance--then the sceptical spirit is _not_ aided by it, but is, contrariwise, weakened.