2 PSYCHOLOGICAL METHODS OF TESTING INTELLIGENCE 



The objection is often made that the problem of 

 intellectual diagnosis can in no way be successfully 

 dealt with until we have exact knowledge of the gen- 

 eral nature of intelligence itself. But this objection 

 does not seem to me pertinent. In science there is no 

 such precise sequence of the different research prob- 

 lems. We measure electro-motive force without 

 knowing what electricity is, and we diagnose with 

 very delicate test methods many diseases the real 

 nature of which we know as yet very little. Indeed, 

 it may be asserted, quite on the contrary, that prog- 

 ress in testing intelligence may shed light from a new 

 angle upon the theoretical study of intelligence and 

 thus supplement the psychology of thinking in a 

 valuable manner. If it turns out, for instance, that 

 certain symptoms are relevant and others irrelevant 

 for the differentiation of the intelligence shown by 

 different persons ; if, again, one series of these symp- 

 toms exhibit a high degree, another series a less de- 

 gree of intercorrelation, then our knowledge of the 

 structure of intelligence must thereby be little by lit- 

 tle increased, and thus there will develop a fruitful 

 reciprocity between the two phases of investigation, 

 theoretical and applied. 



Naturally, we cannot begin our work without a pre- 

 liminary definition of intelligence, however pro- 

 visional it may be. And this definition must be 

 neither too broad nor too narrow. 



Many psychiatrists have used a definition of intel- 

 ligence that is too broad. They use intelligence, in 

 fact, to include mental attainments of all kinds, all 

 those mental qualities, then, that are not volitional 

 or emotional. If this position be taken, it follows, 



