One remark more. Throughout philosophy we do not seek merely for correct, still less for plausible definitions, whose correctness appeals directly to the popular imagination; we seek approved or verified definitions, the content of which is not assumed merely as given, but is seen and known to warrant itself, because warranted by the free self-evolution of thought. To apply this to the present case. However correct and self-evident the definition of quantity usual in Mathematics may be, it will still fail to satisfy the wish to see how far this particular thought is founded in universal thought, and in that way necessary. This difficulty, however, is not the only one. If quantity is not reached through the action of thought, but taken uncritically from our generalised image of it, we are liable to exaggerate the range of its validity, or even to raise it to the height of an absolute category. And that such a danger is real, we see when the title of exact science is restricted to those sciences the objects of which can be submitted to mathematical calculation. Here we have another trace of the bad metaphysics (mentioned in § 98, note) which replace the concrete idea by partial and inadequate categories of understanding. Our knowledge would be in a very awkward predicament if such objects as freedom, law, morality, or even God Himself, because they cannot be measured and calculated, or expressed in a mathematical formula, were to be reckoned beyond the reach of exact knowledge, and we had to put up with a vague generalised image of them, leaving their details or particulars to the pleasure of each individual, to make out of them what he will. The pernicious consequences, to which such a theory gives rise in practice, are at once evident. And this mere mathematical view, which identifies with the Idea one of its special stages, viz. quantity, is no other than the principle of Materialism. Witness the history of the scientific modes of thought, especially in France since the middle of last century. Matter, in the abstract, is just what, though of course there is form in it, has that form only as an indifferent and external attribute.