252 



INDtrCTlON. 



mere statement of the examples, with- 

 out any theoretical discussion, that 

 artificial experimentation is applicable 

 only to the former of these modes of 

 investigation. We can take a cause, 

 and try what it will produce : but we 

 cannot take an effect, and try what it 

 will be produced by. We can only 

 watch till we see it produced, or are 

 enabled to produce it by accident. 



This would be of little importance, if 

 it always depended on our choice from 

 which of the two ends of the sequence 

 we would undertake our inquiries. 

 But we have seldom any option. As 

 we can only travel from the known to 

 the unknown, we are obliged to com- 

 mence at whichever end we are best 

 acquainted with. If the agent is 

 more familiar to us than its effects, 

 we watch for, or contrive, instances 

 of the agent, under such varieties of 

 circumstances as are open to us, and 

 observe the result. If, on the con- 

 trary, the conditions on which a 

 phenomenon depends are obscure, but 

 the phenomenon itself familiar, we 

 must commence our inquiry from the 

 effect. If we are struck with the 

 fact that chloride of silver has been 

 blackened, and have no suspicion of 

 the cause, we have no resource but to 

 compare instances in which the fact 

 has chanced to occur, until by that 

 comparison we discover that in all 

 those instances the substances had 

 been exposed to light. If we knew 

 nothing of the Indian arrows but 

 their fatal effect, accident alone could 

 turn our attention to experiments on 

 the urali ; in the regular course of 

 investigation, we could only inquire, 

 or try to observe, what had been done 

 to the arrows in particular instances. 



Wherever, having nothing to guide 

 us to the cause, we are obliged to set 

 out from the effect, and to apply the 

 rule of varying the circumstances to 

 the consequents, not the antecedents, 

 we are necessarily destitute of the 

 resource of artificial experimentation. 

 We cannot, at our choice, obtain con- 

 sequents as we can antecedents, under 

 any set of circumstances compatible 



with their nature. There are mo 

 means of producing effects but through 

 their causes, and by the sxipposition 

 the causes of the effect in question 

 are not known to us. We have, 

 therefore, no expedient but to study 

 it where it offers itself spontaneously. 

 If nature happens to present us with 

 instances sufficiently varied in their 

 circumstances, and if we are able to 

 discover, either among the proximate 

 antecedents or among some other 

 order of antecedents, something which 

 is always found when the effect is 

 found, however various the circum- 

 stances, and never found when it is 

 not ; we may discover, by mere ob- 

 servation without experiment, a real 

 uniformity in nature. 



But though this is certainly the 

 most favourable case for sciences of 

 pure observation, as contrasted with 

 those in which artificial experiments 

 are possible, there is in reality no case 

 which more strikingly illustrates the 

 inherent imperfection of direct induc- 

 tion when not founded on experimen- 

 tation. Suppose that, by a comparison 

 of cases of the effect, we have found 

 an antecedent which appears to be, 

 and perhaps is, invariably connected 

 with it : we have not yet proved that 

 antecedent to be the cause until we 

 have reversed the process and pro- 

 duced the effect by means of that 

 antecedent. If we can produce the 

 antecedent artificially, and if, when 

 we do so, the effect follows, the in- 

 duction is complete ; that antecedent 

 is the cause of that consequent.* 

 But we have then added the evidence 

 of experiment to that of simple obser- 

 vation. Until we have done so, we 

 had only proved invariable antece- 

 dence within the limits of experience, 

 but not unconditional antecedence or 

 causation. Until it had been shown 



* Unless, indeed, the consequent was 

 generated, not by the antecedent, but by 

 the means employed to produce the ante- 

 cedent. As, however, these means are 

 under our power, there is so far a proba- 

 bility that they are also stiflBciently with- 

 in our knowledge to enable us to judge 

 whether that could be the case or not. 



