ical structure. If we knew that such were the fact, the theory of ions 

 would not be concerned with explaining it. But as we do not know it 

 to be a fact, the theory is unintelligible in that it cannot explain to us 

 how chemical quality can be dependent on mechanical structure. This 

 theory, however, is aided in this aspect by the fact that in other cases 

 within our knowledge, mechanical structure and chemical quality 

 change together. This gives grounds for the inference that a relation- 

 ship exists. 



Instances in which there are no grounds for inferring the existence 

 of a fact, and the possibility of whose existence cannot be understood, 

 are better illustrated by Hyslop's theory. This theory assumes that 

 there is a spirit, which survives death, with all the psycho-physical 

 functions of a living human being. From our experience during life, 

 we know that there is an intimate relation between body and mental 

 function. If the brain is shocked, thinking ceases; if the auditory 

 nerve is destroyed, hearing ceases; if the optic nerve is destroyed, 

 seeing ceases; and if our vocal organs are destroyed or certain brain 

 cells, speaking ceases. Yet this theory assumes that after death the 

 soul without brain, eye, ear or vocal organs performs the functions of 

 thought, seeing, hearing and communicating. Now we do not know 

 from our experience with spirits that they have such powers; as spirits 

 are like nothing in our experience of which we have knowledge, we 

 cannot infer that they have such powers; and, as we cannot compre- 

 hend how spirits can perform such functions, the theory presents an 

 unintelligibility and is thus complex in the fourth sense above defined. 

 The theory presents other typical instances of this kind. The spirits 

 are assumed to be present at almost any place the medium chooses to 

 sit, whether she has come to that place over railroads or across seas. 

 The spirits have no organs of locomotion like any of which we know 

 and therefore their rapid motion is unintelligible to us. Again, spirits 

 are assumed to have power to communicate through the medium with- 

 out the medium being conscious of sights, sounds or touches of spirits ; 

 and the theory assumes that perhaps there is no use of the mediums 

 mental functions at all; that the spirit itself operates the vocal organs 

 to produce the speech of the medium. We do not know these to be 

 facts, we have no analogy to them; and as their possibility cannot be 

 explained they are unintelligibilities. This theory then is found to be 

 complex in the sense that it presents many such incomprehensible ele- 

 ments. 



In the same sense Locke's theory is complex. His theory in- 

 volves the conception of a mind which is like an empty receptacle and 

 becomes filled with ideas, or which is a plastic medium, and ideas be- 

 come impressed upon it. But when Locke speaks of the mind as 



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