ABSTRACTION. 205 



observing minutely and comparing carefully a particular class 

 of phenomena, and an accurate memory for the results of the 

 observation and comparison, so will his conceptions of that 

 class of phenomena be clear; provided he has the indis- 

 pensable habit, (naturally, however, resulting from those other 

 endowments,) of never using general names without a precise 

 connotation. 



As the clearness of our conceptions chiefly depends on the 

 carefulness and accuracy of our observing and comparing facul- 

 ties, so their appropriateness, or rather the chance we have of 

 hitting upon the appropriate conception in any case, mainly 

 depends on the activity of the same faculties. He who by 

 habit, grounded on sufficient natural aptitude, has acquired a 

 readiness in accurately observing and comparing phenomena, 

 will perceive so many more agreements and will perceive them 

 so much more rapidly than other people, that the chances are 

 much greater of his perceiving, in any instance, the agreement 

 on which the important consequences depend. 



6. It is of so much importance that the part of the 

 process of investigating truth, discussed in this chapter, should 

 be rightly understood, that I think it is desirable to restate the 

 results we have arrived at, in a somewhat different mode of 

 expression. 



We cannot ascertain general truths, that is, truths appli- 

 cable to classes, unless we have formed the classes in such a 

 manner that general truths can be affirmed of them. In the 

 formation of any class, there is involved a conception of it as a 

 class, that is, a conception of certain circumstances as being 

 those which characterize the class, and distinguish the objects 

 composing it from all other things. When we know exactly 

 what these circumstances are, we have a clear idea (or concep- 

 tion) of the class, and of the meaning of the general name 

 which designates it. The primary condition implied in having 

 this clear idea, is that the class be really a class ; that it corre- 

 spond to a real distinction ; that the things it includes really 

 do agree with one another in certain particulars, and differ, in 

 those same particulars, from all other things. A person with- 



