OBSERVATION AND EXPERIMENT 221 



effect, accident alone could turn our attention to experiments on the 

 urali : in the regular course ofinvestisration, 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 o])liged 

 to set out from the eftect, and to apply the rule of varying the circum- 

 stances to the consequents, not the antecedents, we are necessarily 

 destitute of the resource of artificial experimentation. We cannot, at 

 our choice, obtain consequents, as we can antecedents, under any set 

 of circumstances compatible with their nature. There are no means of 

 producing effects but through their causes, and by the supposition the 

 causes of the effect in question are not known to us. We have there- 

 fore 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 circumstances, and never found when it is not ; we may 

 discover, by mere observation without experiment, a real uniformity in 

 nature. 



But although this is certainly the most favorable case for sciences of 

 pure observation, as contrasted with those in which artificial experi- 

 ments are possible, there is in reality no case which more strikingly 

 illustrates the inherent imperfection of direct induction when not 

 founded upon experimentation. 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 produced the effect by means of that antecedent. If we can pro- 

 duce the antecedent artificially, and if, when we do so, the effect fol- 

 lows, the induction is complete; that antecedent is the cause of that 

 consequent.* But we then have added the evidence of experiment to 

 that of simple observation. Until we had done so, we had only proved 

 invariaole antecedence, but not unconditional antecedence, or causa- 

 tion. Until it had been shown by the actual production of the antece- 

 dent under kno\Mi circumstances, and the occurrence thereupon of the 

 consequent, that the antecedent was really the condition on which, it 

 depended ; the uniformity of succession which was proved to exist 

 between them might, for aught we knew, be (like the succession of 

 day and night) no case of causation at all ; both antecedent and con- 

 sequent might be successive stages of the effect of an ulterior cause. 

 Observation, in short, without experiment (and without any aid from 

 deduction) can ascertain uniformities, but cannot prove causation. 



In order to see these remarks verified by the actual state of the 

 sciences, we have only to think of the condition of natural history. In 

 zoology, for example, thei'e is an immense number of uniformities 

 ascertained, some of coexistence, othei-s of succession, to many of 

 which, notwithstanding considerable variations of the attendant circum- 

 stances, we know not any exception : but the antecedents, for the 

 most part, are such as we cannot artificially produce ; or, if we can, it 



* Unless, indeed, the consequent was generated not by the antecedent, but by the means 

 we employed to produce the antecedent. As, however, these means are under our power, 

 there is so far a probability that they are also sufficiently within our knowledge, to enable 

 us to judge whether that could be the case or not. 



