What Lord Bacon blames in the schoolmen of his time is this,--that they reasoned syllogistically on words which had not been defined with precision; such as moist, dry, generation, corruption, and so forth. Mr. Mill’s error is exactly of the same kind. He reasons syllogistically about power, pleasure, and pain, without attaching any definite notion to any one of those words. There is no more resemblance, says the Westminster Reviewer, between pain and substantia than between pain and a line or an angle. By his permission, in the very point to which Lord Bacon’s observation applies, Mr. Mill’s subjects do resemble the _substantia_ and _elementum_ of the schoolmen and differ from the lines and magnitudes of Euclid. We can reason _a priori_ on mathematics, because we can define with an exactitude which precludes all possibility of confusion. If a mathematician were to admit the least laxity into his notions, if he were to allow himself to be deluded by the vague sense which words bear in popular use, or by the aspect of an ill-drawn diagram, if he were to forget in his reasonings that a point was indivisible, or that the definition of a line excluded breadth, there would be no end to his blunders. The schoolmen tried to reason mathematically about things which had not been, and perhaps could not be, defined with mathematical accuracy. We know the result. Mr. Mill has in our time attempted to do the same. He talks of power, for example, as if the meaning of the word power were as determinate as the meaning of the word circle. But, when we analyse his speculations, we find that his notion of power is, {104}in the words of Bacon, “_phantastica et male terminata._” There are two senses in which we may use the word _power_ and those words which denote the various distributions of power, as, for example, _monarchy_;--the one sense popular and superficial,--the other more, scientific and accurate. Mr. Mill, since he chose to reason _a priori_, ought to have clearly pointed out in which sense he intended to use words of this kind, and to have adhered inflexibly to the sense on which he fixed. Instead of doing this, he flies backwards and forwards from the one sense to the other, and brings out conclusions at last which suit neither.