tion of matter that it is electrical in nature. But by experiment, the 

 essential characteristics of electricity are determined. By the same 

 method the qualities of matter are revealed. The reasoning then pro- 

 ceeds in this manner: Assume matter to be purely electrical, and its 

 essential qualities can be explained; therefore we infer matter to be 

 electrical. Thus the assumption because of its explaining power be- 

 comes an inference and is no longer purely hypothetical. 



So also the theory of ions though based fundamentally upon the 

 experimental method, makes use of a similar assumption. The 

 existence of the ion, its size, weight and properties are experimentally 

 revealed. The theory then proceeds by assuming that the ions are 

 arranged with a spherical positive electrical charge surrounding the 

 negatively charged ions. There is no direct experimental evidence 

 supporting this assumption; but grant it to be true, and from the 

 known properties of ions, their numbers and arrangements in the 

 atom will be such as to explain to a remarkable degree the Periodic 

 Law. Thus this assumption because of its explaining power be- 

 comes one of the inferences constituting the theory. 



Thus the examination of the theories considered in this paper 

 reveals a class derived by the method of observation and experi- 

 ment, some of the theories making no use of assumptions and others 

 using assumptions which from their explaining power become in- 

 ferences. 



The theories in question exhibit a second distinct class from the 

 point of view of method of procedure. A class from which the 

 thinker proceeds by assuming the existence and nature of things which 

 have not been experimentally investigated and which are like no 

 things in experience. His further procedure consists in developing 

 the logical implications of the assumptions made. Such a method 

 of thinking is John Locke's in his theory concerning human under- 

 standing. Locke assumes a mind to exist and that it has a certain 

 receptive or plastic nature. This assumption is in no way founded 

 upon observation or experiment. And as the mind is like nothing in 

 experience, Locke did not infer its existence by analogy. The mind 

 and its qualities are purely hypothetical. In setting forth Locke's 

 theory, we have already shown that the nature of the idea, the 

 nature of matter and the nature of knowledge were all implied in the 

 assumed nature of mind; and that Locke's further procedure con- 

 sisted in developing these implications. 



Hyslop's thinking shows the use of the same method. Locke 

 had the fact of knowledge given and sought to explain its origin 

 and nature. He did so by assuming a mind of a certain nature to 

 exist. Similarly, Hyslop has the fact of supernormal knowledge 



