was confirmed and believed, was neither true nor false, and only 

 became true as evidence added to its strength and believability ; that 

 when the proposition was first announced, there was no knowledge 

 state in which species represented themselves to have originated in the 

 ascribed manner; that therefore the proposition was sterile, and only 

 as actual knowledge states developed in which species actually implied 

 an origin in the affirmed manner, did the proposition become vital and 

 true. 



It is worthy of note that whichever view one adopts concerning the 

 nature of truth, the practical consequences will be the same. One 

 will confirm his theories in the same way, he will consider it confirmed 

 to the same extent and at the same time ; he will receive and reject the 

 same theories; and the system of required knowledge will be the same 

 to him. Only, one school will insist that a true theory was true and a 

 false theory was false from the time they were asserted as proposi- 

 tions; while the other school will insist that a theory was only true or 

 false from the time and to the extent that its truth or falsity was be- 

 lieved in or appreciated. So far as practice is concerned, one may 

 choose either conception of truth; his choice will have no influence 

 upon his manner of dealing with theories; neither upon their origin 

 nor upon their usefulness. 



IN WHAT SENSE Do THEORIES EXPLAIN. 



In connection with the question of the truth and falsity of theories, 

 I shall consider the question of how far do theories explain; for we 

 should hardly believe that a theory would be considered true or be 

 believed in, which did not explain the phenomena in question. Our 

 research has revealed two distinct kinds of problems and two corre- 

 sponding kinds of explanations or solutions. Where the problem was 

 one of definition, as in the theory that matter is electrical, an explana- 

 tion was made by finding the identity of essential qualities in matter 

 and electricity; and where the problem was one of origin, as in Dar- 

 win's "Origin of Species," an explanation was made by revealing the 

 conditions under which species originated. These were the only two 

 kinds of explanation attempted by any of the thinkers whom we have 

 studied. No attempt was made in the theory that matter is electrical 

 to determine why electricity attracts, or what the essential nature of at- 

 traction is; and no attempt was made by Darwin to show why indi- 

 viduals vary or why inheritance operates. In none of the theories was 

 an attempt made to arrive at final essences or final causes ; and so our 

 study justifies us in saying that the explanation which thinkers succeed 

 in making involve no such determinations. Until then investigation 

 reveals a different kind and a more final explanation, we shall consider 



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