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towards the ideas of Protagoras, but the doctrines 

 which are most closely associated with his name flow 

 from an extension of the Socratic teaching into specu- 

 lations beyond the department of ethics. He found 

 the test of truth in generalisations, which, according 

 to some of his writings, are known to be true because 

 the mind had become acquainted with them in a 

 previous state of existence, and remembers them in 

 the present state. In the Phcedo he describes his 

 method of proof thus : " Laying down some general 

 hypothesis which I considered to be the best, I 

 accepted as truth whatever squared with it, respect- 

 ing cause as well as other things " and " If any one 



impugn the hypothesis I should defend it, 



assuming some other hypothesis yet more general, 

 such as appeared to me to be the best, until I 

 came to something fully sufficient." 



Aristotle (384-322 B.C.) in some of his writings 

 appears to reject this entirely ; in others his dissent is 

 not very decided. The main current of his thought, 

 however, is nearer to that of Protagoras ; he held 

 that truth can be attained by collecting the evidences 

 of sensation, but he is not explicit as to the method 

 (lie calls it the Art) of discovering from these the 

 underlying truths which he sought. He writes, for 

 instance, " Experience furnishes the principles of 

 every science. Thus, astronomy is founded on obser- 

 vation ; for if we were properly to observe the 

 celestial phenomena we might demonstrate the laws 



