TRAINS OF REASONING. 245 



logy, have successively been rendered mathematical; and 

 astronomy was brought by Newton within the laws of general 

 mechanics. Why it is that the substitution 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, prepared to examine. But it is necessary 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 Induction. 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 induc- 

 tion. It is deductive, in proportion as it can draw conclusions, 

 respecting cases of a new kind, by processes which bring those 

 cases under old inductions ; 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 dis- 

 tinction between sciences which can be made Deductive, and 

 those which must as yet remain Experimental. The differ- 

 ence consists in our having been able, or not yet able, to dis- 

 cover marks of marks. If by our various inductions we have 

 been able to proceed no further than to such propositions 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 b with c or d ; we have a science of detached 

 and mutually independent generalizations, 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, is 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 of d, d of e, &c. In these sciences we can mount 



