ABSTRACT
No one denies that, somehow, mental processes are based on physiological processes, but the physiology is unknown, so the phenomena must be discussed in psychological terms. If a man sees a bottle, draws its cork and pours himself out a drink, we can only talk about his actions in terms of ideas, their associations, etc. If enough of his brain were destroyed we know he could not associate the ideas of wine, corkscrew, etc., with sufficient accuracy to govern successful behaviour. We therefore conclude that some brain processes are essential, but as to what they are we have no glimmering. No one can translate the idea “corkscrew” in terms of physiology without being guilty of the grossest tautology. In fact, a little reflection shows a neurologist 1 that our knowledge would have to advance prodigiously before a real translation would be possible. In quite the same way no one can describe the development of a fertilized ovum in terms of physical and chemical reactions, although it is manifest to the biologist that physical and chemical changes are in progress, and that inorganic factors are essential to development. In such cases we are forced to formulate our laws in the language of the science to which the phenomena belong. There are laws of development that are expressed in biological terms; there are laws as to the association of ideas, for instance, that we can put in none but psychological terms.
