ABSTRACTION. 213 



that some idea or mental conception is suggested by a 

 general name, whenever we either hear it or employ 

 it with consciousness of a meaning. And this, which 

 we may call if we please a general Idea, represents in 

 our minds the whole class of things to which the 

 name is applied. Whenever we think or reason con- 

 cerning the class, we do so by means of this idea. 

 And the voluntary power which the mind has, of 

 attending to one part of what is present to it at 

 any moment, and neglecting another part, enables us 

 to keep our reasonings and conclusions respecting 

 the class unaffected by anything in the idea or 

 mental image which is not really, or at least which 

 we do not really believe to be, common to the whole 

 class. 



We have,, then, general conceptions : we can con- 

 ceive a class as a class. But this appears to me to be 

 a fact which Logic, as such, may fairly be permitted 

 to take for granted,, without any particular examina- 

 tion into the manner of it. Logic is concerned with 

 what we can know, and with what we can assert, but 

 not with what we can conceive. We can speak and 

 reason of a number of objects as a class, and we can 

 know them to be a class, and know what makes them 

 so ; and it is enough for Logic to understand this, and 

 to know that the mind has whatever powers this 

 implies, without inquiring what powers these are. 

 However, if we are forced to enter upon this foreign 

 ground, it cannot but be admitted that there are such 

 things as general conceptions, and that when we form 

 a set of phenomena into a class, that is, when we com- 

 pare them with one another to ascertain in what they 

 agree, some general conception is implied in this men-r 

 tal operation. And inasmuch as such a comparison is. 

 a necessary preliminary to Induction, it is most truq 



