APPROXIMATE GENERALIZATIONS, 143 



mining causes, or the presence of counteracting ones, 

 which might be fatal to the approximate generalization. 

 In the case where the approximate proposition is 

 not the ultimatum of our scientific knowledge, but 

 only the most available form of it for our practical 

 guidance ; where we know not only that most A have 

 the attribute B, but also the causes of B, or some 

 properties by which the portion of A which has that 

 attribute is distinguished from the portion which has 

 it not; we are rather more favourably situated than in 

 the preceding case. For we have now a double mode 

 of ascertaining whether it be true that most A are B ; 

 the direct mode, as before, and an indirect one, that 

 of examining whether the proposition admits of being 

 deduced from the known cause, or from the known 

 criterion, of B. Let the question, for example, 

 be, Whether most Scotchmen can read ? We may 

 not have observed, or received the testimony of 

 others respecting, a sufficient number and variety of 

 Scotchmen to ascertain this fact ; but when we con- 

 sider that the cause of being able to read is the having 

 been taught it, another mode of determining the ques- 

 tion presents itself, namely, by inquiring whether 

 most Scotchmen have been sent to schools where 

 reading is effectually taught. Of these two modes, 

 sometimes one and sometimes the other is the more 

 available. In some cases, the frequency of the effect 

 is the more accessible to that extensive and varied 

 observation which is indispensable to the establish- 

 ment of an empirical law; at other times, the fre- 

 quency of the causes, or of some collateral indications. 

 It commonly happens that neither is susceptible of so 

 satisfactory an induction as could be desired, and that 

 the grounds on which the conclusion is received are 

 compounded of both. Thus a man may believe that 



