154 DOGMATISM AND EVOLUTION 



others are supposedly invalid. To think at all we must assume 

 something as true; and what we assume depends upon the pur- 

 pose of our thinking, the kind of conclusion (though, of course, 

 not the particular conclusion) to which we intend our argument 

 to lead. 



Thus, whether our assumed premise regarding the subject 'man' 

 is that he seeks to gratify his desires by the least exertion, or that 

 he possesses a strong religious sentiment, depends upon the nature 

 of our interest. True, in this case the assumption of one of the 

 propositions as valid does not involve the denial of the validity 

 of the other proposition. For the purposes of the economist, 

 the fact that man is religiously inclined is simply negligible 

 it is a meaningless statement so far as his thought is concerned. 

 It is easily seen, however, that the incompatibility between pro- 

 positions concerning the same object, used as premises on different 

 occasions, may amount to explicit contradiction. A remarkable 

 instance of this is found in the physics and biology of the 

 eighteenth century. While the latter had yet to appeal to the 

 intervention of creative power to account for the origin of species, 

 the former had long excluded all intelligent causes from the expla- 

 nation of the cosmos. One may say that in order that physics 

 and bio'ogy might exist, what was true in the one had to be 

 false in the other. And although this particular contradiction 

 no longer exists for contemporary science, there are other no less 

 serious and fundamental difficulties which have arisen in its place. 

 Thus, of the alternative hypotheses of psychophysical parallelism 

 and interaction, the one is preposterous from the point of view 

 of the biologist, who can only regard as absurd the selection and 

 development, on so great a scale, of a function in no wise con- 

 nected with survival; while the other is no less unacceptable 

 to the modern physicist. To be sure, such a contradiction con- 

 stitutes a problem for science, and one which in no particular 

 instance could be branded as insoluble. But we should regard 

 as chimerical the hope that the various sciences will ever be so 

 fully coordinated that the validity of their several laws will in- 

 volve a complete mutual compatibility. 



