that there are such things as tropisms, tactisms, or reaction-systems, how can the behaviorist _study_ such things as “situations,” “adjustments,” and S-R-bonds, how can the materialist _become aware_ of the existence of molecules and atoms, except through the medium of their own conscious or psychic states? States of matter can be known only by means of states of mind, and the former, therefore, cannot be any more real than the latter. “What, after all,” asks Cardinal Mercier, “is a fact of nature if the mind has not seized, examined, and assimilated it? True, the information of consciousness is often precarious. For this reason we do well to aid and control it by scientific apparatus. These apparatus, however, can only aid, never supplant, introspection. The telescope does not replace the eye, but extends its vision.” (“Relation of Exp. Psych. to Philosophy,” pp. 40, 41—Trans. of Wirth.) § 3. The Nature of the Human Soul Now our inner consciousness bears unmistakable witness to the existence within us of an abiding subject of our thoughts, feelings, and desires. In biology, the soul is revealed to us as a binding-principle, that obstructs dissolution of the organism, and a persistent type that maintains its identity amid an incessant flux of matter and flow of energy. Clearer still is testimony of introspective psychology, which reveals all our psychic activities and states as successive modifications of this permanent “I,” “self,” “personality,” or “mind,” according as we choose to express it. Human language proves this most forcibly; for the intramental facts and data of our conscious life simply cannot be so much as intelligibly expressed, much less, defined, or differentiated from the extramental facts of the physical world, without using terms that include a reference to this selfsame persistent subject of thought, feeling, and volition. Even inveterate phenomenalists, like Wundt, James, and Titchener, are obliged to submit to this inexorable linguistic law, in common with their unscientific brethren, the generality of mankind, although they do so only after futile attempts at a “scientific revision” of grammar, and with much grumbling over the “barbarous conceptions” of the gross-headed aborigines who invented human language. Be that as it may, no formulation of mental facts is possible except in terms that either denote or connote this permanent source and ground of human thought and feeling, as is apparent, for example, from such phrases as: “_I_ think,” “_I_ wish,” “_I_ hear”; “_mental_ states” (_i. e._ of the mind); _psychic_ functions (_i. e._ of the psyche); _subjective_ idealism (_i. e._ of the subject); a _conscious_ act (from _con-scire_: “to know along with,” because in conscious acts the subject is known along with the object). The phenomenalists occasionally succeed, in their “most precise” passages, in omitting to mention the person, knower, or thinker behind thought, but they do so only at the cost of