2 74 Heredity. 



When, therefore, we say that mental evolution depends on cere- 

 bral evolution, and, consequently, that psychological heredity 

 depends on physiological, we state a plain truth of experience, a 

 generalization drawn from an immense number of facts. Logically, 

 then, the onus probandi lies with idealism ; it is for the idealists 

 to upset our proposition, not for us to disprove theirs. This is 

 a point in logic too often overlooked, to which we would for a 

 moment call attention. It sometimes happens that a good cause 

 is compromised, because we bring all our strength to bear against 

 the opposite opinion, instead of simply defending our own. A 

 metaphysician, reviving an opinion of Descartes, might hold, as 

 I have heard men hold, the hypothesis of animals being mere 

 machines, and might defy us to prove its falsity. It is possible ; but 

 it is enough for us to reply that the metaphysician has to prove it. 

 Every doctrine that is based on experience and analogy, and that 

 is in accord with the general laws of the universe, must be re- 

 garded as true until the contrary is proved. Of course it may be 

 false, but, at least, it has in its favour presumptions that it is true, 

 and its upholders are under no obligation to refute the opposite 

 doctrines, so long as they are only likely or probable. Such, we 

 take it, is our position in regard to the idealistic thesis. That is, 

 our doctrine rests on experience, against which an a priori theory 

 is of no weight. 



Still, we should not be surprised if to some it savours strongly of 

 materialism. To this difficulty, we might in the first place reply, 

 that if it is true it must nevertheless be accepted, whatever its 

 character ; that it is impossible to protest too strongly against an 

 unphilosophical tendency which would judge doctrines, not accord- 

 ing to their worth, but according to the brand they bear ; and that 

 philosophy cannot approve such a tendency without postponing 

 truth to something else that is to say, without committing suicide. 

 We might also remark that, for us, materialism is only a phantom 

 that disappears so soon as you face it resolutely ; it is like ghosts, 

 which alarm only those who believe in them. But it is better to 

 meet the difficulty face to face, and to show that the objection is 

 without force. 



In the first place, it is clear so long as we confine ourselves to 

 the investigation of second and immediate causes and we shall 



