Now, it would be impertinent for us to raise any objection to the use of such a theory as a working hypothesis in the physical sciences, so long as it does in those sciences the work for which it is required. The object of the physical sciences as a body is simply to enable us to describe and calculate the course of events in nature with the highest degree of accuracy and the least complicated set of formulæ. If this end is most successfully attained by treating a certain group of the properties of sensible things as of primary importance and all the rest as mere derivatives of them, this fact of itself affords sufficient justification for the scientific use of the distinction. For the special objects of physical science any group of properties which thus lends itself to the purposes of description and calculation is of primary importance. But it is no less true that its importance for physical purposes does not afford the least ground for regarding it as equally valuable as a solution of the metaphysical problem of the meaning of substance. For instance, one reason why the mathematical properties of body are of such supreme importance for Physics is that in respect of them bodies can be treated as differing not in kind but only in number. This is why they are of such inestimable service as the basis of our calculations as to the behaviour of things. But it might very well be that the true nature of things is most fully manifested just in those points in which they are different in kind; from the standpoint of the metaphysician, a view of non-human nature, however serviceable, which rests entirely upon the aspects in which things are most alike, may be as superficial as the statistical sociologist’s view of human nature. The true being of a concrete thing may be as inadequately expressed by its mathematical properties as the true character of an individual man by a list of anthropometrical results.[77] In point of fact, we can readily see that the distinction between “primary” and “secondary” qualities, when propounded as an answer to the problem about substance, leaves us just where we were before. For (1) we ascribe the primary qualities to the “substance” of the thing in just the same fashion as the secondary. The thing _is_ of such and such a configuration, _is_ of such and such a mass, _is_ solid, etc.; just as it _is_ rough, or heavy, or green. Or, again, it _has_ configuration, mass, solidity; just as it _has_ weight, taste, colour. Hence the old problem breaks out again with respect to the primary qualities themselves, however the list of them may be constructed. Again we have to ask, what is the _it_ which possesses shape, mass, velocity, etc.?