368 FALLACIES. 



says Professor Playfair*, established some of the ele- 

 mentary propositions of statics by a process in which 

 he " borrows no principle from experiment, but esta- 

 blishes his conclusion entirely by reasoning a priori. 

 He assumes, indeed, that equal bodies, at the ends of 

 the equal arms of a lever, will balance one another ; 

 and also that a cylinder or parallelepiped of homoge- 

 neous matter, will be balanced about its centre of 

 magnitude. These, however, are not inferences from 

 experience ; they are, properly speaking, conclusions 

 deduced from the principle of the Sufficient Reason." 

 And to this day there are few geometers who would 

 not think it far more scientific to establish these or 

 any other premisses in this way, than to rest their 

 evidence upon that familiar experience which in the 

 case in question might have been so safely appealed to. 



6. Another natural prejudice, of most extensive 

 prevalence, and which lay at the root of the errors 

 fallen into by the ancient philosophers in their physi- 

 cal inquiries, was this : That the differences in nature 

 must correspond to our received distinctions ; that 

 effects which we are accustomed, in popular language, 

 to call by different names, and arrange in different 

 classes, must be of different natures, and have diffe- 

 rent causes. This prejudice, so evidently of the same 

 origin with those already treated of, marks more espe- 

 cially the earliest stage of science, when it has not yet 

 broken loose from the trammels of every-day phrase- 

 ology. The extraordinary prevalence of the fallacy 

 among the Greek philosophers may be accounted for 

 by their generally knowing no other language than 

 their own ; from which it was a consequence that 



Dissertation, ut supra, p. 27- 



