two may make five”--where, however, the more recent is grandly consistent as compared with the wavering double-sidedness of the more ancient speculator. The fact of the matter is, that Hartley, like Locke, was swayed at bottom by a sound sense and a lofty religious philosophy which crossed his mechanical theories; whereas the modern thinker, not believing in Mind, properly so called, at all, but only in a bundle of sensations and a thread of associations, like the Romanist Transubstantiation doctors, had no scruple in flinging open defiance in the face of Reason, and making a public ovation of unmitigated nonsense. Such is the natural culmination of all one-sided philosophizing. The seed of a favourite fancy grows up into a stately dogma; the dogma blossoms into a paradox; and the paradox ripens into an absurdity. The extreme nonsensicality of Mill, and the mildly modified error of Hartley with regard to {288} the nature of mathematical evidence, arise from the same cause. They are only the natural expression of the principle that thought is sensation and sensation is thought; thought the matured sensation, and sensation the nascent thought. Mill denies altogether the existence of thought as a distinct thing from sensation; therefore he is quite consistent to say that in some possible world two and two may make five; for it is as a thing thought, and not as a thing perceived, that in the science of number 2+2=4. Mill, in fact, by this paradox, with a hardihood of consistency which is almost sublime, denies the possibility of science altogether; there is no ἐπιστήμη of any kind possible any more than ontology; only ἐμπειρία is possible--an experience of something that is accidentally what it is, and may have been otherwise. This is the highest power of what the Germans call the “Lockian empiricism;” and Mr. Mill in asserting the contingency of all science, has argued, as a good logician could not but do, from that half of the truth of things which it has been the unfortunate destiny of him and his school to mistake for the whole. As for Hartley, he qualifies his one-sidedness with a condition which takes the sting from its nonsense, and, like Locke, saves himself by a very transparent inconsistency; for he talks of a “_necessary_ coincidence” of a certain number of observed equalities with all possible equalities; interpolating thus into the product of sensations the idea of necessity which belongs to a different region altogether, and by no possibility could grow out of a mere succession of sensuous impressions and nervous thrills, however often repeated. A tide-waiter may feel convinced that the tide will {289} flow to-morrow just as it has flowed to-day, and has flowed regularly ever since he began to observe its motions; but no degree of strength in this conviction comes up to the certainty which every sane man has that two and two not only always do make four, and always have made four, but in every possible world must make four.