144 



REASONING 



ing even such truths, relating to com- 

 plex cases, as could be proved, if we 

 chose, by inductions from specific 

 experience. Every branch of natural 

 philosophy was originally experimen- 

 tal ; each generalisation rested on a 

 special induction, and was derived 

 from its own distinct set of observa- 

 tions and experiments. From being 

 sciences of pure experiment, as the 

 phrase is, or, to speak more correctly, 

 sciences in which the reasonings 

 mostly consist of no more than one 

 step, and are expressed by single 

 syllogisms, all these sciences have 

 become to some extent, and some of 

 them in nearly the whole of their 

 extent, sciences of pure reasoning ; 

 whereby multitudes of truths, already 

 known by induction from as many 

 different sets of experiments, have 

 come to be exhibited as deductions or 

 corollaries from inductive propositions 

 of a simpler and more universal char- 

 acter. Thus mechanics, hydrostatics, 

 optics, acoustics, thermology, have 

 successively been rendered mathe- 

 matical ; and astronomy was brought 

 by Newton within the laws of general 

 mechanics. Why it is that the sub- 

 stitution of this circuitous mode of 

 proceeding for a process apparently 

 much easier and more natural, is held, 

 and justly, to be the greatest triumph 

 of the investigation of nature, we are 

 not, in this stage of our inquiry, pre- 

 pared to examine. But it is neces- 

 sary to remark, that although, by 

 this progressive transformation, all 

 sciences tend to become more and 

 more Deductive, they are not, there- 

 fore, the less Inductive ; every step 

 in the Deduction is still an Induc- 

 tion. The opposition is not between 

 the terms Deductive and Inductive, 

 but between Deductive and Experi- 

 mental. A science is experimental, 

 in proportion as every new case, which 

 presents any peculiar features, stands 

 in need of a new set of observations 

 and experiments — a fresh induction. 

 It is deductive, in proportion as it 

 can draw conclusions, respecting cases 

 pf a new kind, by processes which 



bring those cases under old induc- 

 tions ; by ascertaining that cases 

 which cannot be observed to have 

 the requisite marks, have, however, 

 marks of those marks. 



We can now, therefore, perceive 

 what is the generic distinction be- 

 tween sciences which can be made 

 Deductive, and those which must as 

 yet remain Experimental. The dif- 

 ference consists in our having been 

 able, or not yet able, to discover 

 marks of marks. If by our various 

 inductions we have been able to pro- 

 ceed no farther than to such proposi- 

 tions as these, a a mark of b, or a 

 and b marks of one another, c a mark 

 of d, or c and d marks of one another, 

 without anything to connect a or 6 

 with c or d; we have a science of 

 detached and mutually independent 

 generalisations, such as these, that 

 acids redden vegetable blues, and that 

 alkalies colour them green ; from 

 neither of which propositions could 

 we, directly or indirectly, infer the 

 other ; and a science, so far as it is 

 composed of such propositions, ia 

 purely experimental. Chemistry, in 

 the present state of our knowledge, 

 has not yet thrown off this character. 

 There are other sciences, however, of 

 which the propositions are of this 

 kind : a a mark of b, b a. mark of c, 

 c ot d, d of e, &c. In these sciences, 

 we can mount the ladder from a to g 

 by a process of ratiocination ; we can 

 conclude that a is a mark of e, and 

 that every object which has the mark 

 a has the property e, although, per- 

 haps, we never were able to observe 

 a and e together, and although even 

 d, our only direct mark of e, may not 

 be perceptible in those objects, but 

 only inferrible. Or, varying the first 

 metaphor, we may be said to get from 

 a to e underground : the marks b, c, 

 d, which indicate the route, must all 

 be possessed somewhere by the objects 

 concerning which we are inquiring ; 

 but they are below the surface : a is 

 the only mark that is visible, and by 

 it we are able to trace in succession 

 all the rest. 



