From the time of Socrates down to our own time, we find that the chief subject of the ceaseless disputations of the philosophers has been that _ens rationis_, called _soul_. We see the most of them assert its immortality, that is to say, its metaphysical nature; yet others, supported by facts which incontrovertibly prove the entire dependence of the intellect upon the bodily organism, unweariedly maintain the contrary. That soul is by all and before everything taken as _absolutely simple_; for precisely from this its metaphysical nature, its immateriality and immortality were proved, although these by no means necessarily follow from it. For although we can only conceive the destruction of a formed body through breaking up of it into its parts, it does not follow from this that the destruction of a simple existence, of which besides we have no conception, may not be possible in some other way, perhaps by gradually vanishing. I, on the contrary, start by doing away with the presupposed simplicity of our subjectively conscious nature, or the _ego_, inasmuch as I show that the manifestations from which it was deduced have two very different sources, and that in any case the intellect is physically conditioned, the function of a material organ, therefore dependent upon it, and without it is just as impossible as the grasp without the hand; that accordingly it belongs to the mere phenomenon, and thus shares the fate of this,—that the _will_, on the contrary, is bound to no special organ, but is everywhere present, is everywhere that which moves and forms, and therefore is that which conditions the whole organism; that, in fact, it constitutes the metaphysical substratum of the whole phenomenon, consequently is not, like the intellect, a _Posterius_ of it, but its _Prius_; and the phenomenon depends upon it, not it upon the phenomenon. But the body is reduced indeed to a mere idea, for it is only the manner in which the _will_ exhibits itself in the perception of the intellect or brain. The _will_, again, which in all other systems, different as they are in other respects, appears as one of the last results, is with me the very first. The _intellect_, as mere function of the brain, is involved in the destruction of the body, but the _will_ is by no means so. From this heterogeneity of the two, together with the subordinate nature of the intellect, it becomes conceivable that man, in the depths of his self‐ consciousness, feels himself to be eternal and indestructible, but yet can have no memory, either _a parte ante_ or _a parte post_, beyond the duration of his life. I do not wish to anticipate here the exposition of the true indestructibility of our nature, which has its place in the fourth book, but have only sought to indicate the place where it links itself on.