OBSERVATION AND EXPERIMENT. 277 



cover, 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 though this is certainly the most favorable 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 induction 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 produced the effect by means of that ante- 

 cedent. If we can produce the antecedent artificially, and if, when we do 

 so, the effect follows, the induction is complete ; that antecedent is the 

 cause of that consequent.* But we have then added the evidence of ex- 

 periment to that of simple observation. Until we had done so, we had 

 only proved invariable antecedence within the limits of experience, but 

 not unconditional antecedence, or causation. Until it had been shown by 

 the actual production of the antecedent under known 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) not a case of causation at all ; both antecedent 

 and consequent might be successive stages of the effect of an ulterior cause. 

 Observation, in short, without experiment (supposing no aid from deduction) 

 can ascertain sequences and co-existences, but can not 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, there is an immense number of uniformities ascertained, some of 

 co-existence, others of succession, to many of which, notwithstanding con- 

 siderable variations of the attendant circumstances, we know not any ex- 

 ception : but the antecedents, for the most part, are such as we can not 

 artificially produce ; or if we can, it is only by setting in motion the ex- 

 act process by which nature produces them ; and this being to us a myste- 

 rious process, of which the main circumstances are not only unknown but 

 unobservable, we do not succeed in obtaining the antecedents under known 

 circumstances. What is the result ? That on this vast subject, which af- 

 fords so much and such varied scope for observation, we have made most 

 scanty progress in ascertaining any laws of causation. We know not with 

 certainty, in the case of most of the phenomena that we find conjoined, 

 which is the condition of the other ; which is cause, and Avhich effect, or 

 whether either of them is so, or they are not rather conjunct effects of 

 causes yet to be discovered, complex results of laws hitherto unknown. 



Although some of the foregoing observations may be, in technical strict- 

 ness of arrangement, premature in this place, it seemed that a few general 

 remarks on the difference between sciences of mei'e observation and sciences 

 of experimentation, and the extreme disadvantage under which directly in- 

 ductive inquiry is necessarily carried on in the former, were the best prep- 



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

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

 is so far a probability that they are also suflBciently within our knowledge to enable us to 

 judge whether that could be the case or not. 



