Book II. Reality.
Chapter XXII. Nature.
...The question is not whether the principles of physical science possess an absolute truth
to which they make no claim. The question is whether the abstraction, employed by that science, is legitimate and useful And with regard to that question there surely can be no doubt In order to understand the co-existence and sequence of phenomena, natural science makes an intellectual construction of their conditions. Its matter, motion, and force are but working ideas, used to understand the occurrence of certain events. To find and systematize the ways in which spatial phenomena are connected and happen-this is all the mark which these conceptions aim at. And for the metaphysician to urge that these ideas contradict themselves, is irrelevant and unfair. To object that in the end they are not true, is to mistake their pretensions.