The inconsistencies of both Kant and Spencer will illustrate the reluctance of the human mind to acquiesce in a genuine Agnosticism. In the _Critique of Pure Reason_ itself Kant so far contradicts himself as to treat the Thing-in-itself as the cause of sensation, though it is a fundamental doctrine of his system that the concept of causal relation can only be legitimately applied to connect facts inside experience; and in a later work, the _Critique of Judgment_, he tentatively suggests its identity with Will. Of Mr. Spencer it has been truly said (I believe by Mr. F. C. S. Schiller in _Riddles of the Sphinx_) that in the course of his ten volumes of Synthetic Philosophy he speaks much more positively about the nature of the Unknowable than dogmatic theology ventures to speak about the nature of God. Footnote 45: The sceptics of antiquity, who were more alive to this contradiction than most of our modern Agnostics, tried to evade the difficulty by saying that they maintained the unknowability of things not as a demonstrated certainty, but as a “probable opinion.” But this distinction is itself illogical, for unless some propositions are certain there is no ground for considering any one proposition more probable than another. _E.g._ if I know that a die with six faces has four pips on each of two faces, and five pips on only one, I can logically say “it is probable that with this die four will be thrown oftener than five.” If I am totally uncertain what number of pips is marked on the various faces, I cannot regard one throw as more probable than another. Footnote 46: _E.g._, peculiarities of the individual’s colour-spectrum, total and partial colour-blindness, variations in sensibility to musical pitch, etc., etc. Footnote 47: The best known and most popular version of the theory is that of Locke and of a great deal of our popular science, according to which the “primary” qualities of matter, _i.e._ those which have to be treated as fundamental in the physical sciences, are independently real, while the rest are mere effects produced by their action on our sense-organs. The more thorough-going metaphysical doctrines of realists like Leibnitz and Herbart, being much further removed from the “naïve realism” of unreflective common sense, have never enjoyed the same currency. Footnote 48: Compare Ward, _Naturalism and Agnosticism_, vol. ii. p. 178 ff., and Royce, _World and Individual_, First Series, Lect. 3. Prof. Royce’s treatment of Realism, though interesting and suggestive, is perhaps a little too much of a “short and easy way” with the antagonist to be quite convincing. Mr. Hobhouse’s anti-idealistic argument (_Theory of Knowledge_, 517-539) seems to me only to hold good against the “Subjectivism” discussed in our next section, but the reader will do well to examine it thoroughly for himself. Footnote 49: