THE FOUR EXPERIMENTAL, METHODS. 443 



strange that a modified cause, which is in truth a different 

 cause, should produce a different effect. 



Although it is for the most part true that a modification of 

 the cause is followed by a modification of the effect, the 

 Method of Concomitant Variations does not, however, pre- 

 suppose this as an axiom. It only requires the converse 

 proposition ; that anything on whose modifications, modifi- 

 cations of an effect are invariably consequent, must be the 

 cause (or connected with the cause) of that effect ; a propo- 

 sition, the truth of which is evident ; for if the thing itself 

 had no influence on the effect, neither could the modifications 

 of the thing have any influence. If the stars have no power 

 over the fortunes of mankind, it is implied in the very terms, 

 that the conjunctions or oppositions of different stars can have 

 no such power. 



Although the most striking applications of the Method of 

 Concomitant Variations take place in the cases in which the 

 Method of Difference, strictly so called, is impossible, its use 

 is not confined to those cases ; it may often usefully follow 

 after the Method of Difference, to give additional precision to 

 a solution which that has found. When by the Method of 

 Difference it has first been ascertained that a certain object 

 produces a certain effect, the Method of Concomitant Varia- 

 tions may be usefully called in, to determine according to what 

 law the quantity or the different relations of the effect follow 

 those of the cause. 



7. The case in which this method admits of the most 

 extensive employment, is that in which the variations of the 

 cause are variations of quantity. Of such variations we may 

 in general affirm with safety, that they will be attended not 

 only with variations, but with similar variations, of the effect : 

 the proposition, that more of the cause is followed by more of 

 the effect, being a corollary from the principle of the Compo- 

 sition of Causes, which, as we have seen, is the general rule of 

 causation ; cases of the opposite description, in which causes 

 change their properties on being conjoined with one another, 

 being, on the contrary, special and exceptional. Suppose, 



