254 



INDUCTION. 



effects of this cause. If we can either 

 find or produce the agent A in such 

 varieties of circumstances that the 

 different cases have no circumstance 

 in common except A, then whatever 

 effect we find to be produced in all 

 our trials is indicated as the effect of 

 A. Suppose, for example, that A is 

 tried along with B and C, and that 

 the effect is a 6 c ; and suppose that 

 A is next tried with D and E, but 

 without B and C, and that the effect 

 is a d e. Then we may reason thus : 

 b and c are not effects of A, for they 

 were not produced by it in the second 

 experiment ; nor are d and e, for they 

 were not produced in the first. What- 

 ever is really the effect of A must have 

 been produced in both instances ; now 

 this condition is fulfilled by no cir- 

 cumstance except a. The phenomenon 

 a cannot have been the effect of B or 

 C, since it was produced where they 

 were not ; nor of D or E, since it 

 was produced where they were not. 

 Therefore it is the effect of A. 



For example, let the antecedent A 

 be the contact of an alkaline sub- 

 stance and an oil. This combination 

 being tried under several varieties of 

 circumstances, resembling each other 

 in nothing else, the results agree in 

 the production of a greasy and deter- 

 sive or sapmaceous substance: it. is 

 therefore concluded that the combina- 

 tion of an oil and an alkali causes the 

 production of a soap. It is thus we 

 inquire, by the Method of Agreement, 

 into the effect of a given cause. 



In a similar manner we may in- 

 quire into the cause of a given effect. 

 Let a be the effect. Here, as shown 

 in the last chapter, we have only the 

 resource of observation without ex- 

 periment : we cannot take a pheno- 

 menon of which we know not the 

 origin, and try to find its mode of 

 production by producing it : if we 

 succeeded in such a random trial it 

 could only be by accident. But if 

 ■we can observe a in two different 

 combinations, ab c and a d e ; and if 

 we know, or can discover, that the 

 antecedent circumstances in these 



cases respectively were ABC and A 

 D E, we may conclude by a reason- 

 ing similar to that in the preceding 

 example, that A is the antecedent 

 connected with the consequent a by 

 a law of causation. B and C, we 

 may say, cannot be causes of a, since 

 on its second occurrence they were 

 not present ; nor are D and E, for 

 they were not present on its first 

 occurrence. A, alone of the five cir- 

 cumstances, was found among the 

 antecedents of a in both instances. 



For example, let the effect a be 

 crystallisation. We compare instances 

 in which bodies are known to assume 

 crystalline structure, but which have 

 no other point of agreement ; and we 

 find them to have one, and, as far as 

 we can observe, only one, antecedent 

 in common : the deposition of a solid 

 matter from a liquid state, either a 

 state of fusion or of solution. We con- 

 clude, therefore, that the solidifica- 

 tion of a substance from a liquid 

 state is an invariable antecedent of 

 its crystallisation. 



In this example we may go farther, 

 and say, it is not only the invariable 

 antecedent, but the cause, or at least 

 the proximate event which completes 

 the cause. For in this case we are 

 able, after detecting the antecedent 

 A, to produce it artificially, and by 

 finding that a follows it, verify the 

 result of our induction. The import- 

 ance of thus reversing the proof was 

 strikingly manifested when by keep- 

 ing a phial of water charged with 

 siliceous particles undisturbed for 

 years, a chemist (I believe Dr. Wol- 

 laston) succeeded in obtaining crystals 

 of quartz ; and in the equally interest- 

 ing experiment in which Sir James 

 Hall produced artificial marble by the 

 cooling of its materials from fusion 

 under immense pressure ; two admir- 

 able examples of the light which may 

 be thrown upon the most secret pro- 

 cesses of Nature by well-contrived 

 interrogation of her. 



But if we cannot artificially pro- 

 duce the phenomenon A, the conclu- 

 Bion that it is the cause of a remains 



