The Aristotelian argument for the spirituality of the human soul consists in the application of a self-evident principle or axiom to certain facts of internal experience. The axiom in question is the following: “The nature of an agent is revealed by its action”; or, to phrase it somewhat differently: “Every being operates after the same manner that it exists.” The factual data, to which reference is made, are man’s higher psychic functions, in which the soul alone is the active cause and receptive subject, namely: the rational or superorganic functions of thinking and willing. The argument may be formulated thus: Every agent exists after the same manner that it operates. But in rational cognition and volition the soul acts without the co-agency of the material organism. Therefore the human soul can exist without the coexistence of the material organism. But this is tantamount to saying that it is a spiritual reality irreducible to matter and incapable of derivation from matter. For we define that as spiritual, which exists, or is, at least, capable of existing, without matter. Consequently, the human soul is a supermaterial and immortal principle, which does not need the body to maintain itself in existence, and can, on that account, survive the death and dissolution of its material complement, the organism. Such a reality, as we have seen, cannot be a product of evolution, but can only come into existence by way of creation. The axiom, that activity is the expression or manifestation of the entity which underlies it, needs but little elucidation. In the genesis of human knowledge, the dynamic is prior to both the static and the entitive. We deduce the nature of the cause from the changes or effects that it produces. Action, in short, is the primary datum upon which our knowledge of being rests. It is the spectrum of solar light emitted by them, which enables us to determine the nature of the chemical elements present in the distant Sun. It is the reaction of an unknown compound with a test reagent that furnishes the chemist with a clue to its composition and structure. It is the special type of tissue degeneration caused by the specific toxin engendered by an invisible disease germ that enables the pathologists to identify the latter, etc., etc. So much for the axiom. Regarding the psychological facts, a more lengthy exposition is required. To begin with, there is _prima facie_ evidence against the contention that the higher psychic functions in man are independent of the organism. Injury and degeneration of the cerebral cortex result (very often, at least) in insanity and idiocy. Reason, therefore, is in some way dependent upon the organism. Babies, too, are incapable of rational thought until such a time as the nervous system is fully developed. Obviously, then, rational functions cannot be spiritual, inasmuch as they are not independent of the organism.