88 THE SCIENCE OF LOGIC 



the premises of rats ; traps, strychnine, phosphorus, and terriers are various 

 causes between which we must choose : but we do not as a rule hold post 

 mortems on dead rats.&quot; 1 



What Dr. Venn says of the savage and of the ordinary man 

 is also largely true of the scientist : he, too, has a practical as 

 well as a speculative aim in his researches. It is not his sole 

 concern to explain an effect by bringing to light its necessitating 

 and indispensable antecedents, i.e. its reciprocal or commensurate 

 cause : he also wants to discover all the alternative combinations 

 of existing agencies and conditions which embody the indispen 

 sable factors (in inseparable conjunction, perhaps, with many 

 superfluous or indifferent elements) combinations which con 

 stitute so many practical alternative modes of producing the 

 effect in question. 



&quot; Properly speaking,&quot; writes Mr. Joseph, &quot; to give the cause of anything is 

 to give everything necessary, and nothing superfluous, to its existence. Never 

 theless we should often defeat our ends if we gave precisely this ; if our object 

 in seeking the cause of a thing is that we may be able to produce or prevent it, 

 and if something is necessary to its existence which is a property of an object 

 otherwise superfluous, it would be of no use specifying the property necessary 

 unless we specified the otherwise superfluous object in which it was found.&quot; 

 This the author illustrates by remarking : &quot; It may be the texture of the 

 pumice-stone that fits it to remove ink-stains from the skin ; but it would be of 

 more use to tell a man with inky fingers to get a piece of pumice-stone, than 

 to give him a description of the fineness of texture which would render a body 

 capable of making his fingers clean &quot; 3 . Similarly, with regard to the 

 &quot; elasticity &quot; of the air (or other elastic medium) as a cause of the transmission 

 of sound : &quot; We want to know what possessed of the necessary elasticity is 

 present when we hear at a distance ; nor could anyone without knowing that 

 prevent the transmission of sound by removing the elastic medium ; for he 

 would not know what to remove &quot;. 3 



In so far, then, as the scientist has this practical aim before 

 him, he will rest content with discovering &quot; causes &quot; in the wider 

 sense of this term the sense in which an effect can have a 

 &quot; plurality of causes,&quot; i.e. of alternative modes in which it may 

 be produced. Under the influence of this &quot; practical &quot; view of 

 inductive science, Dr. Venn regards this wider conception of 

 cause as &quot; the most serviceable for purposes of inductive logic &quot;.* 

 And in this he is undoubtedly right. But he goes farther, and 

 asserts that the stricter concept of cause that which makes the 

 causal relation reciprocal 



*ofi. cit., p. 275 ; cf. JOSEPH, Logic, p. 446. *ibid., n. 



8 ibid, * Empirical Logic, p. 71. 



