436 INDUCTION, 



the means which mankind possess for exploring the laws of 

 nature by specific observation and experience. 



5. The first of these has been aptly denominated the 

 Method of Eesidues. Its principle is very simple. Subduct- 

 ing from any given phenomenon all the portions which, by 

 virtue of preceding inductions, can be assigned to known 

 causes, the remainder will be the effect of the antecedents 

 which had been overlooked, or of which the effect was as yet 

 an unknown quantity. 



Suppose, as before, that we have the antecedents ABC, 

 followed by the consequents a b c, and that by previous induc- 

 tions (founded, we will suppose, on the Method of Difference) 

 we have ascertained the causes of some of these effects, or the 

 effects of some of these causes ; and are thence apprised that 

 the effect of A is a, and that the effect of B is b. Subtracting 

 the sum of these effects from the total phenomenon, there 

 remains c, which now, without any fresh experiments, we may 

 know to be the effect of C. This Method of Residues is in 

 truth a peculiar modification of the Method of Difference. If 

 the instance A B C, a & c, could have been compared with a 

 single instance A B, a b, we should have proved C to be the 

 cause of c, by the common process of the Method of Differ- 

 ence. In the present case, however, instead of a single 

 instance A B, we have had to study separately the causes 

 A and B, and to infer from the effects which they pro- 

 duce separately, what effect they must produce in the case 

 ABC where they act together. Of the two instances, there- 

 fore, which the Method of Difference requires, the one posi- 

 tive, the other negative, the negative one, or that in which 

 the given phenomenon is absent, is not the direct result of 

 observation and experiment, but has been arrived at by deduc- 

 tion. As one of the forms of the Method of Difference, the 

 Method of Residues partakes of its rigorous certainty, pro- 

 vided the previous inductions, those which gave the effects of 

 A and B, were obtained by the same infallible method, and 

 provided we are certain that C is the only antecedent to which 

 the residual phenomenon c can be referred ; the only agent of 



