theory or hypothesis, and to appreciate the distinction between a "working hypothesis" and a theory advanced with the claim of its final validity or truth.Now, the fact is, that for the purposes of the inquiry to which my book is devoted, I am not directly concerned with the "laboratory function" of "working hypotheses" or physical at all. My object is to consider current physical theories and the assumptions which underlie them in the light of the modern theory of cognition—a theory which has taken its rise in very recent times, and is founded upon the investigation, by scientific methods analogous to those employed in the physical sciences, of the laws governing the evolution of thought and speech. Among the important truths developed by the sciences of comparative linguistics and psychology are such as these: that the thoughts of men at any particular period are limited and controlled by the forms of their expression, viz., by language (using this term in its most comprehensive sense); that the language spoken and "thought in" by a given generation is to a certain extent a record of the intellectual activity of preceding generations, and thus embodies and serves to perpetuate its errors as well as its truths; that this is the fact hinted at, if not accurately expressed, in the old observation according to which every distinct form or system of speech involves a distinct metaphysical theory; that the metaphysical systems in vogue at any particular epoch, despite their apparent differences and antagonisms, on proper analysis are found to be characterized by certain common features in which the latent metaphysics of the language in which such systems have originated, or are presented, are brought to view; that philosophers as well as ordinary men are subject to the thralldom of the intellectual prepossessions embodied in their speech as well as in the other inherited forms of their mental and physical organizations, and are unable to emancipate themselves from this thralldom otherwise than by slow and gradual advances, in conformity to the law of continuity which governs all processes of evolution whatever. It being my belief that all this applies to the votaries of science as well as to the devotees of metaphysics or ontology, I sought to enforce this belief by an examination of the general concepts and theories of modern physics. According to the opinion of contemporary men of science, these concepts and theories are simply generalizations of the data of experience, and are thus not only independent of the old a priori notions of metaphysics, but destructive of them. But, although the founders of modern physical science at the outset of their labors were animated by a spirit of declared hostility to the teachings of mediæval scholasticism a fact which is nowhere more conspicuous than in the writings of Descartes nevertheless, when they entered upon the theoretical discussion of the results of their experiments and observations, they unconsciously proceeded upon the old assumptions of the very ontology which they openly repudiated. That ontology—founded upon the inveterate habit of searching for "essences" by the interpretation of words and the analysis of the concepts underlying them, before the relations of words to thoughts and of thoughts to things were properly understood—was characterized by three great errors: its hypostasis of concepts (notwithstanding the protest of the nominalists against the reification of universals); its disregard of the twofold relativity of all physical phenomena; and its confusion of the order of intellectual apprehension with the order of Nature. These errors gave rise to a number of cardinal doctrines respecting the "substance of things," among which were the assertion of its existence as a distinct thing or real entity, apart from its properties; the further assertion of its absolute permanence and immutability; and, finally, the assertion of the absolute solidity and inertia of its parts and their incapacity to act upon each other otherwise than by contact. And all these doctrines he at the base, not only of Cartesian physics and metaphysics, but of the scientific creed of the great majority of the physicists of the present day. The eminent physicist and physiologist who declares that "before the differential equations of the world-formula could be formed" (i.e., before the ultimate, true, and exhaustive theory of the universe could be constructed), "all processes of Nature must be reduced to the motions of a substratum substantially homogeneous, and therefore totally destitute of quality, of that which appears to us as heterogeneous matter—in other words, all quality must be explained by the arrangement and motion of such a substratum," and the equally distinguished physicist and mathematician who enters upon the attempt at a solution of the problem thus stated by endeavoring to deduce the phenomenal diversities and changes of the universe from imaginary vortical motions of the undistinguishable parts of an assumed universal, homogeneous, continuous, and incompressible fluid, are both as truly instinct with the spirit of the old scientia entis quatenus entis as the most ardent disciple of the Stagirite in the times of Erigena or Aquinas. The physicist who insists upon impact theories of gravitation, cohesion, or chemical affinity, has the same intellectual blood in his veins which coursed in those of the old disputants about "first matter" or "substantial forms." When the Professor of Physics in the University of Edinburgh teaches that matter is absolutely passive, dead, that all physical action is action by contact, that nothing is real which is not indestructible, etc., he stands as unmistakably upon scholastic ontological ground as did Descartes or any of his ecclesiastical contemporaries. The proposition of the modern kinematist, that the true explanation of the phenomena of heat, light, electricity, magnetism, etc., consists in their reduction to the elements of matter and motion, differs in little else than its phraseology from the metaphysical theorem that all the "secondary qualities" of the universal substance are mere specifications or derivatives of its "primary qualities."
The present memoir is an enlargement of a paper which the author presented to the International Conference of Americanists at