Let me add another point of comparison. Aristotle's theory recalls in a striking manner that of Kant on the _a priori_ forms of thought. The form of thought, or the category, is nothing without the matter of cognition, and the latter is nothing without the application of form. "Thoughts without content given by sensation are empty; intuitions without concept furnished by the understanding are blind." There is nothing astonishing in finding here the same illustration, since there is throughout a question of describing the same phenomenon,--the relation of mind to matter. There remains to us to review the principal types of metaphysical systems. We shall discuss these by taking as our guide the principle we have just evolved, and which may be thus formulated: _The phenomena of consciousness constitute an incomplete mode of existence._ FOOTNOTES: [Footnote 40: See [Note 1] on p. 3.] [Footnote 41: For reference, see [Note 18] on p. 73.--ED.] [Footnote 42: _i.e._ rendering actual.--ED.] CHAPTER II SPIRITUALISM[43] AND IDEALISM Flournoy has somewhere written that the chief interest of the systems of metaphysics lies less in the intellectual constructions they raise than in the aspirations of the mind and of the heart to which they correspond. Without taking literally this terribly sceptical opinion, it would be highly useful to begin the study of any metaphysical system by the psychology of its author. The value of each system would be better understood, and their reasons would be comprehended. This book is too short to permit us to enter into such biographical details. I am obliged to take the metaphysical systems _en bloc_, as if they were anonymous works, and to efface all the shades, occasionally so curious, that the thought of each author has introduced into them. Yet, however brief our statement, it seems indispensable to indicate clearly the physical or moral idea concealed within each system. SPIRITUALISM It is known that spiritualism is a doctrine which has for its chief aim the raising of the dignity of man, by recognising in him faculties superior to the properties of matter. We constantly meet, in spiritualism, with the notion of superior and inferior, understood not only in an intellectual sense but also in the sense of moral worth. It will also be remarked, as a consequence of the above principle, that a spiritualist does not confine himself to discussing the ideas of his habitual adversary, the materialist; he finds them not only false, but dangerous, and is indignant with them; some persons even ingenuously acknowledge that they hold firmly to certain principles because they fear to be converted to materialism. I can also discern in this system a very natural horror of death, which inspires in so many people, of whom I am one, both hatred and disgust. The spiritualist revolts against the prospect of a definitive annihilation of thought, and the system he adopts is largely explained as an effort towards immortality.