cause of its failure. 91 



which are enumerated. They did not fail because they neglected to 

 observe facts ; they did not fail because they omitted to class facts ; 

 they did not fail because they had not ideas to reason from ; but they 

 failed because they did not take the right ideas in each case. And so 

 long as they were in the wrong in this point, no industry in collecting- 

 facts, or ingenuity in classing them and reasoning about them, could 

 lead them to solid truth. 



Nor is this account of the nature of their mistake without its m- 

 struction for us; although we are not to expect to derive from the 

 study of their failure any technical rule which shall necessarily guide 

 us to scientific discovery. For their failure teaches us that, in the 

 formation of science, an Error in the Ideas is as fatal to the discover) 

 of Truth as an Error in the Facts ; and may as completely impede 

 the progress of knowledge. I have in Books n. to x. of the Philos- 

 ophy, shown historically how large a portion of the progress of Science- 

 consists in the establishment of Appropriate Ideas as the basis of each 

 science. Of the two main processes by which science is constructed, 

 as stated in Book xr. of that work, namely the Explication of Con- 

 ceptions and the Colligation of Facts, the former must precede the 

 latter. In Book xir. chap. 5, of the Philosophy, I have stated the 

 maxim concerning appropriate Ideas in this form, that the Idea and 

 the Facts must be homogeneous. 



When I say that the failure of the Greeks in physical science arose 

 from their not employing appropriate Ideas to connect the facts, I do 

 not use the term " appropriate" in a loose popular sense ; but I employ 

 it as a somewhat technical term, to denote the appropriate Idea, out of 

 that series of Ideas which have been made (as I have shown in the 

 Philosophy) the foundation of sciences ; namely, Space, Time, Number, 

 Cause, Likeness, Substance, and the rest. It appears to me just to 

 say that Aristotle's failure in his attempts to deal with problems of 

 equilibrium, arose from his referring to circles, velocities, notions of 

 natural and unnatural, and the like, — conceptions depending upon 

 Ideas of Space, of Nature, &c. — which are not appropriate to these 

 problems, and from his missing the Idea of Mechanical Force or Pres- 

 sure, which is the appropriate Idea. 



I give this, not as an account of all failures in attempts at science, 

 but only as the account of such radical and fundamental failures as 

 this of Aristotle ; who, with a knowledge of the facts, failed to connect 

 them into a really scientific view. If I had to compare rival theories 

 of a more complex kind, I should not necessarily say that one involved 



