Page:Mind (New Series) Volume 6.djvu/234

 218 HOWARD V. KNOX: cardinal feature of our everyday life. This fact, too, it is, which gives meaning to the saying, that it is unfair to judge of the wisdom of an action merely by its results. In more general terms : Just as the science of psychology can only be separated from the other sciences by distinguishing between the mental and external worlds ; so the funda- mental principle of biology, that the organism must be in harmony with its material environment, can only have meaning given to it by supposing that environment to have an existence separate from any consciousness that the organism may possess. So intricate and so widely spread is the web of physical causation, that it is impossible for any one to gather up all its threads into his perceptual experience. The perception of one thing means the non- perception of other things : while, at the same time, the unperceived things must be taken into account. This it is that constitutes the unity of Nature. In this part we have so far only been concerned with the conditions which may be specially distinguished as ante- cedent to perception. But the mechanism of perception has also to be regarded as belonging to the external world. Psycho-physics, in fact, is simply the science which cor- relates ' states of consciousness ' with the causal sequence of physical events in general the brain being itself a physical structure, and the changes wrought therein being regarded by psycho-physics as determined by the rest of the material world. But without an external world, as was shown in part i., there is no physical causation at all ; we saw, in fact, that the idea of physical causation presupposes (or rather contains) the notion of exter- nality. Psycho-physics being thus absolutely committed to the assumption of externality, it is absurd to look to it for any solution of the ' question ' whether that ' assump- tion ' is ultimately true. This conclusion is so important, especially in connexion with the relation between neuroses and psychoses, that it will repay us to look at it in this connexion from a more general point of view. In the first place, no one has ever actually perceived, even in some other living being, the neuroses which under- lie psychoses. They are entirely a matter of inference, justified by bringing the more directly known facts of the external world into a comparatively harmonious and in- telligible order. But even if we could perceive the neuroses in others, this perception would be exactly on a par with