them. Thus we conclude that the method of assumption, as revealed 

 in the theories of Locke and Hyslop, will inevitably give rise to a 

 theory complex because it possesses unintelligible elements. 



Having now fully considered the question of simplicity of theories, 

 we shall return to the question of the relation between believability of 

 theories and their simplicity. It will need no discussion to show that 

 simplicity has no bearing upon believability, when we mean by sim- 

 plicity only that the theory has a few concepts simply related; or that 

 the theory possesses no difficult reasonings. The theory of inorganic 

 evolution is simple in both these respects and is a very believable 

 theory. Hyslop's theory is also very simple in both these respects, 

 but is not a believable theory. While the theory of ions is compara- 

 tively complex in these two respects and it is a believable theory. 

 Darwin's theory and the theory that matter is electrical are simple in 

 these respects and are both believable; while Locke's theory, also 

 simple in these respects, is not convincing. It is evident that theories 

 simple in structure and easy to understand in their reasonings, may or 

 may not be believable ; that there is no apparent relation between sim- 

 plicity so understood and believability. Is there any relation between 

 simplicity in the sense of presentable in experience as contrasted with 

 inferred from experience, and believability? Darwin's theory is the 

 most simple of all the theories examined in this respect and is also the 

 most believable. In the theory of ions, the ions and their relationships 

 are inferred existences, and although the theory is very believable, yet 

 just because there is room to doubt the existence of ions and their re- 

 lationships, the theory is less believable than Darwin's. In the theory 

 of inorganic evolution changes of temperature on the sun and stars are 

 inferred existences, and also the appearance and disappearance of ele- 

 ments in those places; yet the methods by which those conditions are 

 discovered have been so thoroughly tested that the evidence leaves no 

 doubt in the mind, and a theory results quite as believable as Dar- 

 win's theory, although in the theory of inorganic evolution the materials 

 of the theory are inferred existences. It is evident that where part or 

 all of the data with which a theory is concerned is inferred existence, 

 that the believability of the theory will be somewhat affected by the 

 strength of the inference of the existence. And that theory which is 

 most simple in this respect, whose materials are for the most part ex- 

 perienced facts, will be the most believable, other conditions being the 

 same. 



It remains to consider the relation between believability and sim- 

 plicity in the fourth sense, where it was denned to mean freedom from 

 unintelligible elements. The most believable theories considered, the 



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