THE FOUR EXPERIMENTAL METHODS. 



253 



by the actual production of the ante- 

 cedent under known circumstances, 

 and the occurrence thereupon of the 

 consequent, that the antecedent was 

 really the condition on which it de- 

 pended ; 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 se- 

 quences and co-existences, but cannot 

 prove causation. 



In order to see these remarks veri- 

 fied 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 caimot arti- 

 ficially produce ; or if we can, it is 

 only by setting in motion the exact 

 process by which nature produces 

 them ; and this being to us a myste- 

 rious process, of which the main cir- 

 cumstances are not only unknown but 

 unobservable, we do not succeed in ob- 

 taining the antecedents under known 

 circumstances. What is the result? 

 That on this vast subject, which 

 affords 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 which 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 

 •trictness of arrangement, premature 



in this place, it seemed that a few 

 general remarks on the difference 

 between sciences of mere observation 

 and sciences of experimentation, and 

 the extreme disadvantage under which 

 directly inductive inquiry is neces- 

 sarily carried on in the former, were 

 the best preparation for discussing 

 the methods of direct induction ; a 

 preparation rendering superfluous 

 much that must otherwise have been 

 introduced, with some inconvenience, 

 into the heart of that discussion. To 

 the consideration of these methods we 

 now proceed. 



CHAPTER VIII. 



OP THE FOUR METHODS OP EXPERI- 

 MENTAL INQUIRY. 



§ I, The simplest and most obvious 

 modes of singling out from among the 

 circumstances which precede or follow 

 a phenomenon those with which it is 

 really connected by an invariable law 

 are two in number. One is, by com- 

 paring together different instances in 

 which the phenomenon occurs. The 

 other is, by comparing instances in 

 which the phenomenon does occur, 

 with instances in other respects simi- 

 lar in which it does not. These two 

 methods may be respectively denomi- 

 nated the Method of Agreement and 

 the Method of Difference. 



In illustrating these methods, it 

 will be necessary to bear in mind the 

 twofold character of inquiries into the 

 laws of phenomena, which may be 

 either inquiries into the cause of a 

 given effect, or into the effects or pro- 

 perties of a given cause. We shall 

 consider the methods in their applica- 

 tion to either order of investigation, 

 and shall draw our examples equally 

 from both. 



We shall denote antecedents by the 

 large letters of the alphabet, and the 

 consequents corresponding to them by 

 the small. Let A, then, be an agent 

 or cause, and let the object of our in- 

 quiry be to ascertain what arc the 



