Ahat phenomena are fully explained either where their qualities are 

 revealed or the conditions of their origin made manifest. 



USEFULNESS OF THEORIES. 



Having considered the simplicity, believability and verifiability of 

 theories in relation to the method by which they were produced, we 

 shall next consider the bearing of these qualities upon the usefulness 

 of theories. And the first essential to a theory being useful is that it be 

 believable ; for until a theory is believed in, it will not be acted upon. 

 Those theories which we found to be most verified and thus most be- 

 lievable: Darwin's theory, the theory of Ions, and the theory of in- 

 organic evolution, we shall expect to find among the useful theories; 

 and those which have not been verified, we shall expect to find of little 

 use. Our investigation has revealed that experimental methods gave 

 rise to verifiable and believable theories and that the method of as- 

 sumption gave rise to theories, difficult of verification and to a small 

 degree believable. Thus there appears a close relationship between 

 the utility of a theory and the method by which it was derived. This 

 will more fully appear when we consider the dependence of utility 

 upon other qualities of theories, which bear a close relationship to 

 method of procedure. We discovered that those theories which were 

 most complex, in the sense that they contained most incomprehensible 

 elements, were the least believable ; and that this quality of complexity 

 was a direct result of the use of the method of assumption and deduc- 

 tion as applied by Locke and Hyslop. We also found that theories 

 derived by this method were most difficult of verification because we 

 could infer nothing concerning the assumed objects out of experience 

 until we had directly investigated their natures. Being difficult of veri- 

 fication, they can gain belief slowly, if at all, and until they have been 

 to some extent verified and have gained belief, they of course will re- 

 main useless in the spheres of practice and thought. 



Our investigation has revealed that the method of assumption and 

 deduction gives rise to theories complex in the sense of containing in- 

 comprehensible elements; difficult of verification because they assume 

 the existence of things out of experience like no things in experience; 

 unbelievable because no evidence is offered for the existence of the as- 

 sumed things and because there is in our experience nothing analogous 

 to them making their nature intelligible to us ; and, finally, useless be- 

 cause to no extent verified and believed. On the contrary, our investi- 

 gation has revealed that theories derived by the method of observation 

 and experiment are simple in the sense that they possess few or no 

 unintelligible elements; are verifiable from the fact that the existences 

 which they imply out of experience are like existences in experience and 



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