662 EXPERIMENTAL PSYCHOLOGY 



habits of the adult mind and the processes of its earlier develop- 

 ment, the types of mental action in the normal subject and their 

 variations under conditions of disease, the phenomena of human 

 consciousness and those of lower forms of life afford data for sys- 

 tems of knowledge which, while forming mutually assistive parts 

 of one general science, are yet profitably regarded as separable 

 groups of organized facts. But no such differentiation can legiti- 

 mately be made between experimental and theoretical psych- 

 ology. By virtue of its very demonstration, each fact becomes at 

 once an element in the system of relations which theoretical psych- 

 ology is constructing. Experimental psychology is thus a term 

 which describes the whole process by which our knowledge of mental 

 functions and relations is put upon an inductive basis. It connotes 

 the transformation which has withdrawn psychology from affiliation 

 with philosophy and has placed it among the natural sciences. It is 

 by its very nature coextensive with the field of theoretical psych- 

 ology, for the subject-matter is a continuum, and therefore admits 

 of but one mode of approach. 



The range of instances to which the experimental method has 

 been applied, and the fruitfulness of its results in any given sub- 

 class of mental phenomena depend upon the special conditions 

 under which these experiences arise; and the value of its con- 

 tributions varies greatly from one group of psychoses to another. 

 But the existence of these difficulties is a thing wholly mechanical 

 and irrelevant. The entire field of psychology belongs to the psych- 

 ologic experimentalist; and only when every part of systematic 

 psychology has been put upon a substantial inductive basis shall 

 we be in possession of a secure body of doctrine. 



The functional relation w r hich I have just indicated is subject 

 to confusion through the rise of a group of loosely related appella- 

 tions, each of which in turn has been employed to designate the 

 field of experimental psychology. Psychometry, psycho-physics, men- 

 tal physiology, physiological psychology, experimental psychology, 

 and empirical psychology are terms whose proper applications differ 

 so significantly as to make their discrimination indispensable. 



In the present connection, however, we are concerned only with 

 indicating the limits of physiological psychology, a field indi- 

 cated also by the illogical and unhappy term mental physiology. 

 This term has not infrequently been used as a substitute for ex- 

 perimental psychology, and in untechnical speech is perhaps most 

 in vogue for this purpose. Properly it is a much more restricted 

 term; for the system of physiological changes which in some form 

 or another is the uniform accompaniment of mental phenomena 

 comes under consideration only here and there in the general course 

 of psj^chological investigation. This series of events is indeed one 



