If a scientific prediction, or law, is to be something more than a vague statement of what will probably occur, we feel the necessity of measuring the quantity of the event; that is, our minds are not satisfied until we are able to express it mathematically. Since the only measurable attributes, concerning which our opinion of more or less is definite, are geometrical lengths, the aim of all science is, and must be, to express its laws in the language of mechanics; for that subject alone deals exclusively with simple, sensible masses and their geometrical relations in space. We have then the paradox that while mathematics is the goal of science, in that it is the ideal method, or language of expression, it is not itself a science since it is concerned with subjective ideas and is not limited by the restrictions of sensible bodies. Modern men of science may rebel against this fact; but even the newer, and more dubious, of the pseudo-sciences are forced to substantiate their claims with the support of factitious mathematical formulæ and tables and to simulate the mechanistic method. The inevitable tendency of science is to investigate all phenomena quantitatively, and to view the whole universe as a vast and measurable machine. If the phenomena of life are to be classed as an exact science, it is necessary to postulate that the living organism, also, is a machine,--a thing of various material parts, acting on each other by mechanical forces. Such a postulate is pure _fiat_, for we have found no common factors between what we call vital actions and mechanical and physical forces. Biology is, at best, confined to the discovery of qualitative classifications, and the mutual chemical and physical reactions of the organism; and life is so complex and so variable that very few of its phenomena can be predicted with any accuracy. For example, the so-called law of heredity is often cited, but we have made scarcely any progress towards predicting variations in even an immediately succeeding generation. Even if a general law of progressive evolution were granted to have been established, no one could foretell by it the future variations of any species. If the scientific method is badly strained when applied to even the simplest forms of life, it completely fails when used to elucidate the phenomena of the mind. The fundamental definition of science excludes the processes of consciousness from its field, for it assumes that objective phenomena are to be interpreted by the mind. If we attempt to study the mind objectively, then we come face to face with the absurd paradox of a thing investigating itself by means of I itself. And the gibe cast at the scientific psychologists, that they propose to study the mind by first denying its existence, is only too well founded.