SECT. 20.] Arrangement and Formation of the Series. 49 



tempts to apply the methods of science in the region of the 

 mind, this proposal has met with some opposition; with very 

 slight reason, as it seems to me. That our mental qualities, 

 if they could be submitted to accurate measurement, would 

 be found to follow the usual Law of Error, may be assumed 

 without much hesitation. The known extent of the correla 

 tion of mental and bodily characteristics gives high proba 

 bility to the supposition that what is proved to prevail, at 

 any rate approximately, amongst most bodily elements which 

 have been submitted to measurement, will prevail also 

 amongst the mental elements. 



To what extent such measurements could be carried 

 out practically, is another matter. It does not seem to 

 me that it could be done with much success; partly be 

 cause our mental qualities are so closely connected with, 

 indeed so run into one another, that it is impossible to 

 isolate them for purposes of comparison 1 . This is to some 

 extent indeed a difficulty in bodily measurements, but it is 

 far more so in those of the mind, where we can hardly get 

 beyond what can be called a good guess. The doctrine, 

 therefore, that mental qualities follow the now familiar law 

 of arrangement can scarcely be grounded upon anything 

 inore than a strong analogy. Still this analogy is quite 

 strong enough to justify us in accepting the doctrine and 

 all the conclusions which follow from it, in so far as our 

 estimates and measurements can be regarded as trustworthy. 

 There seems therefore nothing unreasonable in the attempt 

 to establish a system of natural classification of mankind 

 by arranging them into a certain number of groups above 

 and below the average, each group being intended to cor- 



1 I am not speaking here of the measurement of perceptions and other 

 now familiar results of Psychophysics, simple states of consciousness, 

 which are mainly occupied with the 



v. 4 



