462 OPERATIONS SUBSIDIARY TO INDUCTION. 



thing which has not those common properties, nor exclude from it any 

 thing Avhich has. A clear conception means a determinate conception ; 

 one which does not fluctuate, which is not one thing to-day and another 

 to-morrow, but remains fixed and invariable, except when, from the prog- 

 ress of our knowledge, or the correction of some error, we consciously add 

 to it or alter it. A person of clear ideas is a person who always knows in 

 virtue of what properties his classes are constituted ; w^hat attributes are 

 connoted by his general names. 



The principal requisites, therefore, of clear conceptions, are habits of at- 

 tentive observation, an extensive experience, and a memory which receives 

 and retains an exact image of what is observed. And in proportion as 

 any one has the habit of observing minutely and comparing carefully a 

 particular class of phenomena, and an accurate memoiy for the results of 

 the observation and comparison, so will his conceptions of that class of 

 phenomena be clear ; provided he has the indispensable 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 faculties, so their appropri- 

 ateness, or rather the chance we have of hitting upon the appropriate con- 

 ception 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 deisend. 



§ 6. It is of so much importance that the part of the process of investi- 

 gating 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 some- 

 Avhat different mode of expression. 



We can not ascertain general truths, that is, truths applicable 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 conception) of the class, and of 

 the meaning of the general name which designates it. The primary condi- 

 tion implied in having this clear idea, is that the class be really a class ; 

 that it correspond 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 without clear ideas is one 

 who habitually classes together, under the same general names, things 

 which have no common properties, or none which are not possessed also 

 by other things ; or who, if the usage of other people prevents him from 

 actually misclassing things, is unable to state to himself the common prop- 

 erties in virtue of which he classes them rightly. 



But is it not the sole requisite of classification that the classes should be 

 real classes, framed by a legitimate mental process ? Some modes of class- 

 ing things are more valuable than others for human uses, whether of spec- 

 ulation or of practice ; and our classifications are not well made, unless the 

 things which they bring together not only agree with each other in some- 



