6/2 THE AMERICAN JOURNAL OF SOCIOLOGY
while the former embodies in its subject-matter and point of view the subject-matter and points of view of the latter in a manner which makes the differentiating from each other of the sciences concerned a matter of less ease than might be supposed. One or two illustrations may help to make clear what is meant here. Before a given science (let us say psy- chology) shall be able to deal to the best advantage with cer- tain phenomena (as those of vision), other sciences (in this case physics, chemistry, anatomy, and physiology) must each in turn have dealt to the fullest of their capabilities with the phenomena in question ; and in so doing they will have prepared the phe- nomena' for the psychologist's consideration. Here the pro- paedeutic relation, sustained by the first four sciences mentioned to psychology, is very plain. Another instance may better serve us in making more explicit the meaning implied in the reference to the second phase of this relation, made some lines above. Suppose we are bent upon an understanding of a commonplace hand clasp. We may say roughly that physics would be con- cerned with it as a group of physical changes ; chemistry, as a group of chemical changes ; anatomy, as an assemblage of bodily structures; physiology, with the functioning of these structures. Psychology would consider it in its bearing upon the structure and function of consciousness.
If this were all, the thing might be simple enough ; but, unfor- tunately, things are not so simple here as they seem. In the case of the actual hand clasp we get no chemical change without including a physical change also ; we get no functioning of the bodily structures without having bound up with it both chemical changes and physical changes ; and we get no functioning with- out appropriate structures. When the psychologist comes to consider, in its relation to consciousness, this complex of phe- nomena we call a hand clasp, he must deal with it as an assem- blage of bodily structures, as a functioning of these structures, as a group of chemical changes, and as a group of physical changes ; and in so dealing with it he must use the light thrown
■ The same thing may be put from the other side by saying, " prepared the psy- chologist to investigate the phenomena."
