empty, he evidently does not mean spatially empty, and that ideas are 

 space occupying things which fill it. Yet a relation between mind and 

 ideas is involved in the theory, and Locke describes this relation by 

 saying that the empty is filled. Yet this emptiness is like no emptiness 

 of which we have had experience, and the filling is like no filling of 

 which we know. The relationship is, therefore, unintelligible. The 

 same is true of the conception that ideas are impressed upon the mind. 

 Locke here evidently does not mean impressed in the physical sense. 

 Yet there is no other sense of the word which we can conceive of as 

 applicable. The theory asserts that mind and ideas are intimately 

 related, but the relationship is like no relationship of which we have 

 knowledge, and is, therefore, an unintelligible one. 



Locke's theory also involves the conception that ideas resemble or 

 copy objects. When it is said that one thing resembles another or 

 copies it, it is meant that the two are alike in characteristic respects. 

 But Locke evidently does not mean that the idea is solid and extended 

 like the object or that it possesses any of the characteristic qualities of 

 the object. The resembling or copying, then, which Locke refers to, 

 is like no resembling or copying of which we know and is thus incom- 

 prehensible to us. 



This element of unintelligibility which we have considered as a 

 condition of complexity in a theory is also displayed by Locke's con- 

 ception of real knowledge. The theory is that because some ideas re- 

 semble objects, that therefore knowledge concerned with these ideas, 

 is knowledge of the objects themselves. And Locke considers that we 

 know some knowledge to be real. The acceptance of the theory would 

 necessitate one's believing that the mind knew of the relationship be- 

 tween ideas and things, although knowledge is but the perception of 

 the relations between ideas. How the understanding reaches a knowl- 

 edge of the relation between ideas and things is to one accepting the 

 theory incomprehensible. Our examination of Locke's theory then 

 reveals many unintelligible elements, and thus we shall agree that the 

 theory is complex in this sense. 



It may be helpful here to call attention to two conditions of un- 

 intelligibility which the theories in question reveal, one of which makes 

 the theory more complex and the other does not. In Darwin's 

 theory, we know that individual variations are inherited. We de- 

 termine this to be a fact by observing parent and offspring. Yet we 

 know little of the laws of inheritance; of how inheritance is accom- 

 plished. This, however, does not affect the complexity of Darwin's 

 theory ; for the theory needs for its purposes only the fact that there 

 is inheritance. When the fact is known, the theory is not concerned 

 with the question of how it is possible. In the theory of ions, how- 



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