perception, volition etc., can also be expressed in terms of physical concepts such as: stimulus, response, brain process, nervous discharge, and so forth. If this is correct, it may be regarded as a justification of certain ideas from which the metaphysical views of Democritus and his followers have sprung, but Materialism itself, as a metaphysic, remains as nonsensical as before. The question of metaphysics is so important that I may perhaps be permitted to give another illustration of the way in which it disappears from our philosophy.
Descartes, as is well known, maintained the view that only human beings were endowed with "consciousness" and that we must look upon animals as mere automata behaving exactly "as if" they were "conscious" creatures, but in reality being condemned to a "soulless" existence. One may easily and justly point out that Descartes' argument might be extended to our human fellow-beings. How can I ever be sure that my human brothers and sisters are more than mechanical automata and possess a consciousness similar to my own?
Most philosophers, I believe, are inclined to regard the question as a genuine question, and to answer it in this way: the behaviour of all human beings, and also the behaviour of all animals, down to insects and worms, is, in the most important respects so similar to my own behaviour, that I must infer the existence of consciousness "within" them; it is an inference by analogy, it is true, but based on such striking correspondence that it must be regarded as valid with a degree of probability which can hardly be distinguished from certainty. Nevertheless these philosophers admit that the probability is not exactly equal to 1. That it is not absolute certainty, and that here we are confronted with a case where absolute certainty can never be gained. According to their opinion the existence of consciousness in beings other than myself is a typical unsolvable problem. There is no imaginable way of deciding it. — What are we to think of it ? Our verdict is simple: if the question is really definitely unanswerable it can be only because there is no meaning in it. And if this is so, if there is no problem at all, there can be no probable answer either, it must be nonsense to assert that animals and human beings "very likely" possess consciousness. We can speak of probability only where there is at least a theorical possibility of discovering the truth.
