390 THE PRINCIPLES OF SCIENCE. 



partly arises from the fact, that so high a philosophical 

 authority as Mr. Herbert Spencer has denied that gene 

 ralization is implied in abstraction&quot;, making this doctrine 

 the ground for rejecting previous methods of classifying 

 the sciences, and for forming an ingenious but peculiar 

 method of his own. The question is also a fundamental 

 one of the highest logical importance, and involves subtle 

 difficulties which have made me long hesitate in forming 



1 . . . O 



a decisive opinion. 



Let us attempt to answer the question by examination of 

 a few examples. Compare the two classes gun and iron 

 gun. It is certain that there are many guns which are 

 not made of iron, so that abstraction of the circumstance 

 made of iron increases the extent of the notion. Next 

 compare gun and metallic gun. All guns made at the 

 present day consist, I believe, of metal, so that the two 

 notions seem to be co-extensive ; but guns were at first made 

 of pieces of wood bound together like a tub, and as the 

 logical term gun takes no account of time, it must include 

 all guns that have ever existed. Here again extension 



. o 



increases as intension decreases. Compare once more 

 steam-locomotive engine and locomotive engine. In 

 the present day so far as I am aware all locomotives are 

 worked by steam, so that the omission of that qualifica 

 tion might seem not to widen the term ; but it is quite 

 possible that in some future age a different motive power 

 may be used in locomotives ; and as there is no limitation 

 of time in the use of logical terms, we must certainly 

 assume that there is a class of locomotives not worked by 

 steam, as well as a class that is worked by steam. 

 When the natural class of Euphorbiacese Avas origin 

 ally formed, all the plants known to belong to it were 

 devoid of corollas ; it would have seemed therefore that 

 the two classes Euphorbiacese/ and Euphorbiacese devoid 



x The Classification of the Sciences, &c., 3rd edit. p. 7. 



