The question of personal immortality stands on a somewhat different footing. Here evidence either way is possible. Persons are part of the everyday world with which science is concerned, and the conditions which determine their existence are discoverable. A drop of water is not immortal; it can be resolved into oxygen and hydrogen. If, therefore, a drop of water were to maintain that it had a quality of aqueousness which would survive its dissolution, we should be inclined to be sceptical. In like manner we know that the brain is not immortal, and that the organized energy of a living body becomes, as it were, demobilized at death, and therefore not available for collective action. All the evidence goes to show that what we regard as our mental life is bound up with brain-structure and organized bodily energy. Therefore it is rational to suppose that mental life ceases when bodily life ceases. The argument is only one of probability, but it is as strong as those upon which most scientific conclusions are based. There are various grounds upon which this conclusion might be attacked. Psychical research professes to have actual scientific evidence of survival, and undoubtedly its procedure is, in principle, scientifically correct. Evidence of this sort might be so overwhelming that no one with a scientific temper could reject it. The weight to be attached to the evidence, however, must depend upon the antecedent probability of the hypothesis of survival. There are always different ways of accounting for any set of phenomena, and of these we should prefer the one which is antecedently least improbable. Those who already think it likely that we survive death will be ready to view this theory as the best explanation of psychical phenomena. Those, who, on other grounds, regard this theory as unplausible will seek for other explanations. For my part, I consider the evidence so far adduced by psychical research in favour of survival much weaker than the physiological evidence on the other side. But I fully admit that it might at any moment become stronger, and in that case it would be unscientific to disbelieve in survival.