466 FALLACIES. 



that one of these caii possibly be more natural than the other. All 

 these fancies of the possibility of knowing what is natural or not natural 

 by any other means than experience, are, in truth, entirely futile. The 

 real and only proof of the laws of motion, or of any other law of the 

 universe, is experience ; it is simply that no other suppositions explain 

 or are consistent with the facts of universal nature. 



Geometers have, in all ages, been open to the imputation of en- 

 deavoring to prove the most general facts of the outward world by 

 sophistical reasoning, in order to avoid appeals to the senses. Archi- 

 medes, says Professor Playfair,* established some of the elementary 

 propositions of statics by a process in which he "boiTows no pi-inciple 

 from experiment, but establishes his conclusion entirely by reasoning 

 d priori. He assumes, indeed, that equal bodies, at the ends of the 

 equal arms of a lever, "vvill balance one another ; and also that a cylin- 

 der or parallelepiped of homogeneous matter, wall 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 philoso- 

 phers in their physical inquiries, was this: That the differences in 

 nature must con-espond to our received distinctions ; that effects which 

 we are accustomed, in popular language, to call by different names, 

 and aiTange in different classes, must be of difterent natures, and have 

 different causes. This prejudice, so evidently of the same origin with 

 those already treated of, marks more especially the earliest stage of 

 science, when it has not yet broken loose from the trainmels of every- 

 day phraseology. The extraordinary prevalence of the fallacy among 

 the Greek philosophers may be accounted for by theii' generally know- 

 ing no other language than their own ; from which it was a consequence 

 that their ideas followed the accidental or arbitrary combinations of 

 that language, more completely than can happen among the modems 

 to any but illiterate persons. They had gi'eat difl[iculty in distinguish- 

 ing between things which their language confounded, or in putting 

 mentally together things which it distinguished ; and could hardly com- 

 bine the objects in nature into any classes but those which were made 

 for them by the popular phrases of their own country ; or at least 

 could not help fancying those classes to be natural, and all others 

 arbitrary and artificial. Accordingly, as is remarked by Mr. Whewell, 

 scientific investigation among the Greek philosophers and their fol- 

 lowers in the middle ages, was little more than a mere sifting and 

 analyzing of the notions attached to common language. They thought 

 that by determining the meaning of words, they could become ac- 

 quainted with facts. " They took for granted," says Mr. Whewell, t 

 "that philosophy must result from the relations of those notions which 

 are involved in the common use of language, and they proceeded to 



* Dissertation, ut supra, pp. 298-9. 



t History of the Inductive Sciences, Book i., chap. 1. 



