CRITEEIA OF SCIENTIFIC TRUTH. 155 



to compel us to accept its contradictory. The fourth 

 commands that we seek the causes and laws that have 

 determined the existence of our subject, for the subject 

 cannot be adequately known except in these. So that the 

 vaunted criteria of truth are rules of evidence ; and there 

 is no one means of judging of truth, except what the 

 whole science of evidence affords.' l 



The criterion given by Sir J. Herschel, viz., agreement 

 with universal experience or evidence, is an excellent one. 

 Truth in science is complete real consistency with universal 

 nature, and the ultimate test and criterion of truthful- 

 ness of all scientific ideas is real conformity with all the 

 great principles of science, including the laws of identity, 

 contradiction, and duality ; the principles of uniformity 

 of nature, of continuity, conservation and equivalency of 

 matter and force, of action and reaction, the laws of 

 motion, &c. 2 



These and a number of other important tests in science, 

 constitute not only the criteria of scientific truth, but also 

 furnish the laws of proof, and determine the value of 

 evidence in scientific questions. When we prove a state- 

 ment in science, we show by evidence that it is in 

 accordance with the great principles of nature and does 

 not contradict any of them ; that it is identical with, or 

 similar to, other known and admitted truths ; that there 

 is a sufficient reason for the existence of the subject of the 

 statement ; and that it cannot be otherwise on account of 

 the causes and conditions present. 



4 We have to notice a distinction which is found to 

 prevail in the progress of true and false theories. In the 

 former class, all the additional suppositions tend to sim- 

 plicity and harmony ; the new suppositions resolve them- 



1 Outline of the Laws of Thought, p. 210. 



2 See Chapter XIV. 



