199. The quarrel of the physiologist with the metaphysician is, in fact, due to an _ignorantia elenchi_ on the part of the former, for which the behaviour of English ‘metaphysicians,’ in attempting to assimilate their own procedure to that of the natural philosophers, and thus to win the popular acceptance which these alone can fairly look for, has afforded too much excuse. The question really at issue is not between two co-ordinate sciences, as if a theory of the human body were claiming also to be a theory of the human soul, and the theory of the soul were resisting the aggression. The question is, whether the conceptions which all the departmental sciences alike presuppose shall have an account given of them or no. For dispensing with such an account altogether (life being short) there is much to be said, if only men would or could dispense with it; but the physiologist, when he claims that his science should supersede metaphysic, is not dispensing with it, but rendering it in a preposterous way. He accounts for the formal conceptions in question, in other words for thought as it is common to all the sciences, as sequent upon the antecedent facts which his science ascertains--the facts of the animal organisation. But these conceptions--the relations of cause and effect, &c.--are necessary to constitute the facts. They are not an _ex post facto_ interpretation of them, but an interpretation without which there would be no ascertainable facts at all. To account for them, therefore, as the result of the facts is to proceed as a geologist would do, who should treat the present conformation of the earth as the result of a certain series of past events, and yet, in describing these, should assume the present conformation as a determining element in each. Hume’s psychology will not answer it either.