144 INDUCTION. 



most Scotchmen can read, because, so far as his 

 information extends, most Scotchmen have been sent 

 to school, and most Scotch schools teach reading 

 effectually ; and also because most of the Scotchmen 

 whom he has known or heard of, could read; though 

 neither of these two sets of observations may by itself 

 fulfil the necessary conditions of extent and variety. 



Although the approximate generalization may in 

 most cases be indispensable for our guidance, even 

 when we know the cause, or some certain mark, of 

 the attribute predicated ; it needs hardly be observed 

 that we may always replace the uncertain indication 

 by a certain one, in any case in which we can actually 

 recognise the existence of the cause or mark. For 

 example, an assertion is made by a witness, and the 

 question is, whether to believe it. If we do not look 

 to any of the individual circumstances of the case, 

 we have nothing to direct us but the approximate 

 generalization, that truth is more common than false- 

 hood, or, in other words, that most persons, on most 

 occasions, speak truth. But if we consider in what 

 circumstances the cases when truth is spoken differ 

 from those in which it is not, we find, for instance, 

 the following : the witness's being an honest man or 

 not ; his being an accurate observer or not ; his 

 having an interest to serve in the matter or not. 

 Now, not only may we be able to obtain other 

 approximate generalizations respecting the degree of 

 frequency of these various possibilities, but we may 

 know which of them is positively realized in the indi- 

 vidual case. That the witness has or has not an inte- 

 rest to serve, we may know directly; and the other 

 two points indirectly, by means of marks; as, for 

 example, from his conduct on some former occasion; 

 or from his reputation, which, though not a sure mark, 



