432 



OPERATIONS SlTBSIDIARY TO INDUCTION. 



§ 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 re- 

 sults we have arrived at, in a some- 

 what different mode of expression. 



We cannot 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 con- 

 ception of it as a class, that is, a con- 

 ception of certain circumstances as 

 being those which characterise 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 

 condition 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 in- 

 cludes 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 pro- 

 perties in virtue of which he classes 

 them rightly. 



But it is 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 

 speculation or of practice ; and our 

 classifications are not well made un- 

 less the things which they bring to- 

 gether not only agree with each other 

 in something which distinguishes 

 them from all other things, but agree 

 with each other and differ from other 



things in the very circumstances which 

 are of primary importance for the pur- 

 pose (theoretical or practical) which 

 we hav« in view, and which consti- 

 tutes the problem before us. In other 

 words, our conceptions, though they 

 may be clear, are not appropriate for 

 our purpose, unless the properties we 

 comprise in them are those which 

 will help us towards what we wish to 

 understand — i.e., either those which 

 go deepest into the nature of the 

 things, if our object be to understand 

 that, or those which are most closely 

 connected with the particular property 

 which we are endeavouring to investi- 

 gate. 



We cannot, therefore, frame good 

 general conceptions beforehand. That 

 the conception we have obtained is 

 the one we want, can only be known 

 when we have done the work for the 

 sake of which we wanted it ; when 

 we completely understand the general 

 character of the phenomena, or the 

 conditions of the particular property 

 with which we concern ourselves. 

 General conceptions formed without 

 this thorough knowledge are Bacon's 

 "notiones temer^ a rebus abstractae." 

 Yet such premature conceptions we 

 must be continually making up in 

 our progress to something better. 

 They are an impediment to the pro- 

 gress of knowledge only when they 

 are permanently acquiesced in. When 

 it has become our habit to group 

 things in wrong classes — in groups 

 which either are not really classes, 

 having no distinctive points of agree- 

 ment (absence of clear ideas), or which 

 are not classes of which anything im- 

 portant to our purpose can be predi- 

 cated (absence of appropriate ideas) ; 

 and when, in the belief that these 

 badly mad eclasses are those sanctioned 

 by Nature, we refuse to exchange 

 them for others, and cannot or will 

 not make up our general conceptions 

 from any other elements ; in that case 

 all the evils which Baccm ascribes to 

 his "notiones temerd abstracts " really 

 occur. This was what the ancients did 

 in physics, and what the world in gene- 



