It may, perhaps, seem absurd, even to suppose, that we should think ourselves able to change, by a few generic words, the properties of the substances which we have classed; and if the question were put to us, as to this effect of our language, in any particular case, there can be no doubt, that we should answer in the negative, and express astonishment that such a question should have been put. But the illusion is not the less certain, because we are not aware of its influence; and, indeed, it could no longer be an illusion, if we were completely aware of it. It requires, however, only a very little reflection on what has passed in our own minds, to discover, that, when we have given a _name_ to any quality, that quality acquires immediately, in our imagination, a comparative importance, very different from what it had before; and though nature in itself be truly unchanged, it is ever after, relatively to our conception, different. A difference of words is, in this case, more than a mere verbal difference. Though it be not the expression of a difference of doctrine, it very speedily becomes so. Hence it is, that the same warfare, which the rivalries of individual ambition, or the opposite interests, or supposed opposite interests, of nations have produced, in the great theatre of civil history, have been produced, in the small but tumultuous field of science, by the supposed incompatibility of a few abstract terms; and, indeed, as has been truly said, the sects of philosophers have combated, with more persevering violence, to settle what they mean by the constitution of the world, than all the conquerors of the world have done to render themselves its masters.