substituting _personal pronouns_, and of thus bringing back through the window what they have just ejected by way of the door. Our consciousness, therefore, makes us invincibly aware of the _existence_ of a superficially variable, but radically unchangeable, subject of our mental life. It does not, however, tell us anything concerning the _nature_ of this primary ground of thought, whether, for example, it is identical with the cerebral cortex, or something distinct therefrom, whether it is phenomenal or substantial, dynamic or entitive, spiritual or material. To decide these questions the unanalyzed factual data of internal experience do not suffice, but they do suffice to establish the reality of the ego or subject of thought. Later we shall see that the analysis of these data, when taken in conjunction with other facts, forces us to predicate of the soul such attributes as substantiality, simplicity, and spirituality, but here they are cited solely for their factual force and not for their logical implications. The phenomenalistic schools of Interactionism and Psychophysical Parallelism deny the _substantiality_ of the soul, and seek to resolve it into sourceless and subjectless processes. A phenomenal mind or soul, however, could not be the primary ground of mental life, for the simple reason that phenomena presuppose a supporting medium (otherwise they would be self-maintaining, and therefore, substantial). Now that which presupposes cannot be a primary principle, but only a secondary, or tertiary principle. Consequently, a functional mind could not be the primary and irreducible ground of mental life, but only that _of which_ it is a function, whether that something is a material, or a spiritual substance. For the present, we are not interested in the nature of this ultimate substrate, we are content with the fact that it really exists. Phenomenalists (like Wundt, Paulsen, and James) are very inconsistent when they admit material molecules as the extended substrate of extramental or physical phenomena, while denying the existence of the mind or ego as the inextended substrate of intramental or psychic phenomena. All substance, whether material or spiritual, is inaccessible to the senses. Even material substrates are manifested only by their phenomena, being in themselves supersensible and “metaphysical.” If, then, the human understanding is inerrant in ascribing a material substrate to extramental phenomena, then it is equally inerrant in attributing to intramental phenomena the intimate substrate called mind, whether this substrate be a spiritual substance, or a material substance like the substrate of physical phenomena and that of organic life. As a matter of fact, the Psychophysical Parallelists actually do reduce mental phenomena to a material substrate (viz. the cerebral cortex). Their phenomenalism, which we will refute presently, is but a disingenuous attempt to gloss over their fundamental materialism.