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a rational basis of knowledge till comparatively 

 recent times. The later Greeks were, in general, 

 content to take as truth anything for which they 

 could find authority in the accepted traditions of the 

 particular school to which they had attached them- 

 selves. In the same spirit mediaeval Christians referred 

 every question to the authority of the Church ; a 

 course which was more prudent because any deviation 

 therefrom was visited by the most tremendous penal- 

 ties. Even when the tyranny of this authority was 

 at last breaking down, Copernicus (1473-1543) 

 was obliged to introduce his heliocentric system of 

 astronomy with an apology. The form which this 

 took is memorable, because, hesitating as it was, it 

 explicitly stated, for the first time, the principle 

 upon which all science depends. He pleaded that, 

 although the theory might not be true, yet it should 

 be tolerated because it had the advantage of simplify- 

 ing, and thus facilitating, astronomical calculation. 



It will be remembered that in 1633, nearly a 

 century later, Galileo was imprisoned at Rome and 

 threatened with torture by the Inquisition for his 

 advocacy of the Copernican theory. 



Descartes (1596-1650) seems to stand at the part- 

 ing of the ways ; for him there is a body of external 

 truth dependent upon the will of the Deity, but known 

 to man, presumably because it has been in some way 

 revealed. " The metaphysical truths, styled eternal, 

 have been established by God, and like the rest of 



