what the theory affirmed it to be; the method by which the theory 

 was derived makes it possible to review its procedure and correct any 

 error in its determinations. The theory is for this reason strongly 

 believable. 



In the theory of a future life, quite different conditions maintain. 

 We have shown that this theory was derived by the method of as- 

 sumption and deduction ; and that the strength of the theory depended 

 upon the strength of the assumptions. If spirits exist with memories, 

 power of rapid motion, power of communication between themselves 

 and between them and human beings, then supernormal knowledge is 

 explained. But if one doubts that a spirit survives the human body, 

 that it can move without 'being substantial, that it can see, hear, and 

 understand without eyes, ears or brain; or that it can operate the 

 physical mechanism of voice production with all its intricate muscular 

 combinations, in the entranced subject; doubt these assumptions and 

 the theory will not be believed. Now from the method by which the 

 theory was derived, these facts were not experimentally determined. 

 They were not directly investigated by the author of the theory and 

 no other person interested in showing their truth or falsity can at 

 present investigate them. The method of procedure is such that its 

 affirmations cannot be reviewed by methods which will finally deter- 

 mine their truth or falsity, until the theory is put upon an experimental 

 basis, at which time it will no longer be a theory of assumption and 

 deduction. As the method by which the theory was derived does not 

 present its data in a believable state, the theory does not carry con- 

 viction. From this examination we conclude that there is a signifi- 

 cant relationship between method of procedure and believability of 

 theories; that the experimental method generally leads to believable 

 theories, while the method of assumption and deduction from its 

 nature does not. 



We shall also attempt to show that believability depends to some 

 extent upon the simplicity of a theory. However, before dealing 

 with this question it will be necessary to consider this quality of a 

 theory, called its simplicity, at length. 



SIMPLICITY OF THEORIES. 



Upon an investigation of these theories which we are here study- 

 ing, we find that there are four different qualities of the theories which 

 might be designated by the term simplicity or complexity. I shall set 

 forth these different meanings in order. 



First, simple may mean simple in structure ; the quality will depend 

 upon the number of concepts in the theory and the number of their 

 relationships. This meaning for the word simple as applied to a 



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