are predominantly classificatory, can never rival the Cosmological Sciences in exactness; but they may reach a fuller knowledge; and their certainty will assume more and more the character of exactness as methods of measurement are applied to their classifications of qualities. The qualitative and quantitative aspects of phenomena are handled by the two great instruments, Logic and Mathematics, the second being only a special form of the first. These determine the general conceptions which are derived from our perceptions, and the whole constitute Experience. 8. What is the conclusion to which these considerations lead? It is that the separation of the quantitative from the qualitative aspect of phenomena--the objective mechanical from the subjective psychological--is a logical artifice indispensable to research; but it is only an artifice.[206] In pursuance of this artifice, each special science must be regarded as the search after special analytical results; and meanwhile this method should be respected, and no confusion of the boundaries between one science and another should be suffered. Mechanical problems must not be confused by the introduction of biological relations. Biological problems must not be restricted to mechanical relations. I do not mean that the mechanical relations present in biological phenomena are not to be sought, and, when found, to be expressed in mechanical terms; I mean that such an inquiry must be strictly limited to mechanical relations. Subjective relations are not to be denied, because they are provisionally set aside, in an inquiry into objective relations; but we must carefully distinguish which of the two orders we are treating of, and express each in its appropriate terms. This is constantly neglected. For example, nothing is more common than to meet such a phrase as this: “A _sensory impression_ is transmitted as a _wave_ of _motion_ to the brain, and there being transformed into a state of _consciousness_, is again reflected as a _motor_ impulse.” The several sciences having attained certain analytical results, it remains for Philosophy to co-ordinate these into a doctrine which will furnish general conceptions of the World, Man, and Society. On the analytical side a mechanical theory of the universe might be perfected, but it would still only be a theory of mechanical relations, leaving all other relations to be expressed in other terms. We cannot accept the statement of Descartes that Nature is a vast mechanism, and Science the universal application of mathematics. The equation of a sphere, however valuable from a geometrical point of view, is useless as an explanation of the nature and properties of the spherical body in other relations. And so a complete theory of the mechanical relations of the organism, however valuable in itself, would be worthless in the solution of a biological problem, unless supplemented by all that mechanical terms are incompetent to express.