510 INDUCTION. 



is the cause of a; but that it is either the cause or 

 another effect of the same cause, may be placed 

 beyond any reasonable doubt by the Method of Agree- 

 ment, provided the instances are very numerous, as 

 well as sufficiently various. 



After how great a multiplication, then, of varied 

 instances, all agreeing in no other antecedent, except 

 A, is the supposition of a plurality of causes suffi- 

 ciently rebutted, and the conclusion that a is the 

 effect of A divested of the characteristic imperfection 

 and reduced to a virtual certainty ? This is a ques- 

 tion which we cannot be exempted from answering ; 

 but the consideration of it belongs to what is called 

 the Theory of Probability, which will form the subject 

 of a chapter hereafter. It is seen, however, at once 

 that the conclusion does amount to a practical 

 certainty after a sufficient number of instances, and 

 that the method, therefore, is not radically vitiated 

 by the characteristic imperfection. The result of 

 these considerations is only, in the first place, to 

 point out a new source of inferiority in the Method of 

 Agreement as compared with other modes of investi- 

 gation, and new reasons for never resting contented 

 with the results obtained by it, without attempting to 

 confirm them either by the Method of Difference, or 

 by connecting them deductively with some law or 

 laws already ascertained by that superior method. 

 And,, in the second place, we learn from this, 

 the true theory of the value of mere number of 

 instances in inductive inquiry. The tendency of 

 unscientific inquirers is to rely too much upon num- 

 ber, without analysing the instances ; without looking 

 closely enough into their nature, to ascertain what 

 circumstances are or are not eliminated by means of 

 them. Most people hold their conclusions with a 



