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this opinion. When the question of the origin of 

 knowledge was next discussed from an independent 

 philosophical standpoint, Hobbes and Locke were 

 able to show that no basis of scientific knowledge 

 other than sensation is possible, and Locke pointed 

 out moreover the practical nature of such knowledge, 

 which is essentially of the kind suited for the 

 guidance of action. Hume took up the question 

 where Locke had left it, and found that although 

 knowledge had been shown to rest, in some way 

 or another, on a basis of sensation, yet an intelligible 

 theory was required as to the mental process by 

 which the two were connected. He did not him- 

 self propose any such theory ; he indicated very 

 clearly the nature of the problem, but was obliged 

 to leave it unsolved because at that period the data 

 necessary for a solution were not available. Hume 

 was about sixteen when Xewton died, so that 

 science, in the modern sense of the term, was still 

 of very recent growth and its nature was not yet 

 thoroughly understood. We have seen that Newton 

 and his contemporaries imagined it to be a dis- 

 closure of pre-existing decrees whereby phenomena 

 are caused and governed ; a discovery which ob- 

 viously could not be attained through the senses. 

 It has been shown, however, from the subsequent 

 history of science, that in the course of its develop- 

 ment many hypotheses have been changed ; that 

 in every case the change has been made because 



