The soul is simple, others say, because it reflects upon itself as a complete whole. No; the state of consciousness A, in which I think of my previous state of consciousness B, is not the same as its predecessor. Or if I think of my soul, I think of an idea distinct from the act by which I think of it. To think that one thinks and nothing more, is not to think.
The soul is the principle of life, it is said. Yes; and similarly the category of force or energy has been conceived as the principle of movement. But these are concepts, not phenomena, not external realities. Does the principle of movement move? And only that which moves has external reality. Does the principle of life live? Hume was right when he said that he never encountered this idea of himself--that he only observed himself desiring or performing or feeling something.[27] The idea of some individual thing--of this inkstand in front of me, of that horse standing at my gate, of these two and not of any other individuals of the same class--is the fact, the phenomenon itself. The idea of myself is myself.
All the efforts to substantiate consciousness, making it independent of extension--remember that Descartes opposed thought to extension--are but sophistical subtilties intended to establish the rationality of faith in the immortality of the soul. It is sought to give the value of objective reality to that which does not possess it--to that whose reality exists only in thought. And the immortality that we crave is a phenomenal immortality--it is the continuation of this present life.
The unity of consciousness is for scientific psychology--the only rational psychology--simply a phenomenal unity. No one can say what a substantial unity is. And, what is more, no one can say what a substance is. For the notion of substance is a non-phenomenal category. It is a noumenon and belongs properly to the unknowable--that is to say, according to the sense in which it is understood. But in its transcendental sense it is something really unknowable and strictly irrational. It is precisely this concept of substance that an unforewarned mind reduces to a use that is very far from that pragmatic application to which William James referred.