Survival of bodily death is, however, a different matter from immortality: it may only mean a postponement of psychical death. It is immortality that men desire to believe in. Believers in immortality will object to physiological arguments, such as I have been using, on the ground that soul and body are totally disparate, and that the soul is something quite other than its empirical manifestations through our bodily organs. I believe this to be a metaphysical superstition. Mind and matter alike are for certain purposes convenient terms, but are not ultimate realities. Electrons and protons, like the soul, are logical fictions: each is really a history, a series of events, not a single persistent entity. In the case of the soul, this is obvious from the facts of growth. Whoever considers conception, gestation, and infancy cannot seriously believe that the soul is an indivisible something, perfect and complete throughout this process. It is evident that it grows like the body, and that it derives both from the spermatozoon and from the ovum, so that it cannot be indivisible. This is not materialism: it is merely the recognition that everything interesting is a matter of organization, not of primal substance. Metaphysicians have advanced innumerable arguments to prove that the soul _must_ be immortal. There is one simple test by which all these arguments can be demolished. They all prove equally that the soul must pervade all space. But as we are not so anxious to be fat as to live long, none of the metaphysicians in question have ever noticed this application of their reasonings. This is an instance of the amazing power of desire in blinding even very able men to fallacies which would otherwise be obvious at once. If we were not afraid of death, I do not believe that the idea of immortality would ever have arisen. Fear is the basis of religious dogma, as of so much else in human life. Fear of human beings, individually or collectively, dominates much of our social life, but it is fear of nature that gives rise to religion. The antithesis of mind and matter is, as we have seen, more or less illusory; but there is another antithesis which is more important――that, namely, between things that can be affected by our desires and things that cannot be so affected. The line between the two is neither sharp nor immutable――as science advances, more and more things are brought under human control. Nevertheless there remain things definitely on the other side. Among these are all the _large_ facts of our world, the sort of facts that are dealt with by astronomy. It is only facts on or near the surface of the earth that we can, to some extent, mould to suit our desires. And even on the surface of the earth, our powers are very limited. Above all, we cannot prevent death, although we can often delay it.