322 THE FOUNDATIONS OF ZOOLOGY 



The whole aim and purpose of the Essay on Classification is 

 to prove that all the general laws of natural science are "cate- 

 gories of thought," by an attempt to show that they are nothing 

 but categories of thought, and that no physical explanation of 

 them is possible. 



In 1859, or less than two years after the publication of the 

 Essay on Classification, the appearance of the "Origin of Species" 

 brought about a revolution in our conceptions of natural history, 

 for it made clear the mechanical explanation of some of the 

 general laws of which Agassiz had told us no such explanation 

 is possible. It is because the work of Wallace and Darwin has 

 convinced naturalists that species have arisen, in course of nature, 

 through influences that are still at work, that many modern stu- 

 dents have refused to follow Agassiz in the assertion that the 

 laws of their science are "arbitrary," for they hold that these 

 laws are neither arbitrary nor necessary, but natural. 



As Agassiz used, as the basis of his thesis that nature is a 

 language, the assertion that the laws of living nature are not 

 mechanical, many of the working naturalists of our day, know- 

 ing, in part at least, the physical explanation of these laws, have 

 refused to share his conviction that nature is a language; for it 

 is the fate of beliefs which are upheld by fallacious reasoning to 

 suffer from the mistakes of their supporters. It is clear, how- 

 ever, that error on the part of the advocate of an opinion is no 

 proof of error in the opinion itself. The intuitions which told 

 Agassiz that nature is a language, which we learn to our delight 

 and profit and instruction, may have been sound and trustworthy 

 and fruitful in results, even if the reasons he gives for this con- 

 viction are at fault. 



An illustration may make this clear. As the same thought 

 may be expressed in various ways in different languages, and 

 as even in the same language the same sounds or letters may 

 have many meanings, it is clear that there is no "necessary" 

 connection between words and the things they signify ; for we 

 might call black white, and white black, without confusion, if all 

 who use our language were agreed upon the meaning of these 

 words. As the relation between words and the things they signify 

 is not "necessary," it has seemed to some that it is " arbitrary "; 



