If we have the ideas and the words, the process of thought, as Hobbes has taught us, is nothing but an addition and subtraction of ideas. We add when we say, A is B; when we say, for instance, man, or Caius, is mortal, adding Caius, or man, to all that we call mortal; we subtract when we say, A is not B; that is, when we abstract Enoch from all that we call mortal. Everything that man has ever thought, humiliating as it may sound, consists in these two operations; just as the most abstruse operations of mathematics go back in the end to addition and subtraction. To what else could they go back? Whether these mental operations are true or false, is another question, with which the method of the thinker has nothing to do; any more than formal logic inquires whether all men are mortal, but only infers on the basis of these premises that Caius, because he is a man, is also mortal. We see, therefore, how language and thought go hand in hand; where there is as yet no word, there is not yet an idea. The thinking capacity of the mind has its source in language, lives in language, and develops continuously in language. The human mind is human language, and as animals possess no language, they do not _ipso facto_ possess what philosophers understand by mind. We need not for this reason ascribe any special faculty to men. Speech and thought are only a wider development of the faculty of presentation such as an animal may have; but in an animal it never develops any farther, for an animal has no general ideas; it remains at the individual, and never attains unity in plurality. It knows, as Plato would say, a horse, but not “horsedom.” If we wish to say that the perceiving self is present in animals as in men, there is no objection, though in all such, questions relating to animals we are always groping in the dark. But the fact remains that the step, whether small or vast, that leads from the individual to the general, from the concrete to the abstract, from perceiving (that is, being acted upon) to conceiving, thinking, speaking, that is, to acting, is for the animal impossible. An animal might speak, but it cannot; a stone might grow, but it cannot; a tree might walk, but it cannot. Why not? Because there are natural boundaries that are apparently easy to pass, and yet impassable. The tree grows up a tree, the animal an animal, but no farther, just as man never surpasses the human, and therefore can never think except through language, which often is very imperfect.