466 THE POPULAR SCIENCE MONTHLY 



This insistence involves the substitution of a doctrine of mental 

 characters for the popular conception of vague and indefinite traits and 

 peculiarities. How is this doctrine to be derived? Obviously from 

 psychology itself. Neither biometry nor biology nor common sense 

 can furnish the materials. 



Look with me for a moment, if you will, to see what psychology has 

 to offer. It is evident that the general psychology of the average 

 normal mind will not suffice when the matter is one of defining differ- 

 ences among minds of the same class. Just as physical inheritance 

 must take account of arrays and schemes of distribution, and not of 

 averages, so must mental qualities and magnitudes be arranged with 

 respect to definite individual variations within the class. 



A psychology of individual differences is thus invoked; and a 

 psychology of individual differences does exist; or rather, it is in 

 process. The way of scientific description is first to reveal uniformities 

 hidden in the mass, and afterward to seek the rule of variation from 

 the average. General psychology, taken in this sense, is accordingly 

 the older branch of the science — the psychology of what is common to 

 all minds — individual psychology, the newer. So it happens that 

 although the older branch of the science has a well-developed metrical 

 technique, established at almost the same moment that " The Origin 

 of Species " appeared, its quantitative determinations are determina- 

 tions of psychophysical constants and not laws of individual variation. 

 These laws can not then be used (at least not directly) for the statis- 

 tical study of inheritance. What is needed is a psychology of typical 

 differences, and this it is that individual psychology is by way of sup- 

 plying. Let me, in a word, indicate its method. It proceeds by ex- 

 periment to take the dimensions of mind as regards variable functions, 

 e. g., the maximal amount read in a given time and under given con- 

 ditions, or the number of words remembered or of figures added. The 

 first results show typical differences as between mind and mind. The 

 experimenter next proceeds to factor the performance into elementary 

 processes and functions. By drawing his conditions closer and closer 

 he discovers that the capacity for reading depends upon such simple 

 factors as the range of consciousness, the degree of attention, and the 

 temporal rate of visual processes, factors all capable of measurement 

 and exact description. He discovers that remembrance depends upon 

 the employment of visual or auditory or kinesthetic processes, i. e., that 

 in one observer an eye-mind, in another an ear-mind and in a third a 

 muscle-mind is employed. Of these factors, he can predicate heritabil- 

 ity. It is as if " criminality " were reduced to a lack of motor control 

 plus an abnormally intensive passion or lust. " Criminality " would 

 then never be inherited, but the constituent factors might very well be. 

 The method of individual psychology, however, goes farther. After 



