METHOD OF DISCO VERING CA USAL LA WS 1 73 



canons in question. They have been stated in a variety of ways, 

 nowhere, perhaps, more clearly than in Dr. Mellone s Introductory 

 Text-book of Logic, 1 whose treatment of the subject we purpose 

 mainly to follow. 



The first rule, which is called the METHOD OF AGREEMENT, or 

 of single agreement, he states in this wise : 



&quot; WHEN OBSERVATION SHOWS THAT TWO EVENTS ACCOMPANY 

 ONE ANOTHER (EITHER SIMULTANEOUSLY OR IN SUCCESSION), IT 

 IS PROBABLE THAT THEY ARE CAUSALLY CONNECTED ; AND THE 

 PROBABILITY INCREASES WITH THE NUMBER AND VARIETY OF 



THE INSTANCES.&quot; 



This rule is based on the principle that whatever can be re 

 moved or eliminated without interfering with the phenomenon 

 is not causally connected with the latter ; and hence it is thus 

 briefly expressed by Mr. Joseph : 2 &quot; Nothing is the cause of a 

 phenomenon in the absence of which it nevertheless occurs &quot;. It 

 is a method of observation mainly, i.e. a rule to which we have 

 recourse when we cannot experiment. Its chief utility lies in the 

 fact that it suggests a causal connexion as an hypothesis for verifi 

 cation. What appears to be the sole invariable antecedent of a 

 phenomenon probably contains the &quot; necessitating and indispens 

 able cause &quot; of the latter ; though other things also may contain 

 this &quot; necessitating and indispensable cause &quot;. Hence, at best, 

 this rule merely suggests (without proving) that our &quot; sole in 

 variable antecedent &quot; is a cause (in the wider sense) of the phe 

 nomenon. And since it suggests (without proving) only a cause 

 in the wider sense, it does get us over the difficulty arising from 

 the fact that the same phenomenon can have a plurality of such 

 causes. Briefly, it fails to prove a reciprocating causal relation 

 because what we think to be the sole invariable antecedent (i) 

 may not be so de facto (since another may be invariably present 

 unknown to us) ; and therefore, possibly, (2} may not be relevant 

 to the phenomenon at all (since the latter may be in reality due 

 to the unknown antecedent) ; and (3) even though the observed 

 invariable antecedent is de facto the one which, when present, 

 necessitates the effect, it need not be indispensable to the latter ; 

 for it may merely contain this indispensable element plus some 

 thing irrelevant, while (for all we know) this indispensable ele 

 ment may be equally well supplied by each of the varying 



J chap. ix. ^op. cit., p. 403. 



