208 INDUCTION. 



§ 2. For the purposes of the present inquhy, Induction may be defined, 

 the operation of discovering and proving general propositions. It is true 

 that (as already shown) the process of indirectly ascertaining individual 

 facts, is as truly inductive as that by which we establish general truths. 

 But it is not a different kind of induction ; it is a form of the very same 

 process : since, on the one hand, generals are but collections of particulai's, 

 definite in kind but indefinite in number ; and on the other hand, whenever 

 the evidence which we derive from observation of known cases justifies us 

 in drawing an inference respecting even one unknown case, we should on 

 the same evidence be justified in drawing a similar inference with respect 

 to a Avhole class of cases. The inference either does not hold at all, or it 

 holds in all cases of a certain description ; in all cases which, in certain de- 

 finable respects, resemble those we have observed. 



If these remarks are j ust ; if the principles and rules of inference are the 

 same whether we infer general propositions or individual facts ; it follows 

 that a complete logic of the sciences would be also a complete logic of prac- 

 tical business and common life. Since there is no case of legitimate infer- 

 ence from experience, in which the conclusion may not legitimately be a 

 general proposition ; an analysis of the process by which general truths ai'e 

 arrived at, is virtually an analysis of all induction whatever. Whether we 

 "are inquiring into a scientific principle or into an individual fact, and wheth- 

 er we proceed by experiment or by ratiocination, every step in the train of 

 inferences is essentially inductive, and the legitimacy of the induction de- 

 jiends in both cases on the same conditions. 



True it is that in the case of the practical inquirer, who is endeavoring 

 to ascertain facts not for the purposes of science but for those of business, 

 such, for instance, as tlie advocate or the judge, the chief difiiculty is one in 

 which the principles of induction will afford him no assistance. It lies not 

 in making his inductions, but in the selection of them; in choosing from 

 among all general propositions ascertained to- be true, those which furnish 

 marks by which he may trace whether the given subject possesses or not 

 the predicate in question. In arguing a doubtful question of fact before 

 a jury, the general propositions or principles to which the advocate ap- 

 peals are mostly, in themselves, sufficiently trite, and assented to as soon as 

 stated : his skill lies in bringing his case under those propositions or princi- 

 ples ; in calling to mind such of the known or received maxims of probabil- 

 ity as admit of application to the case in hand, and selecting from among 

 them those best adapted to his object. Success is here dependent on nat- 

 ural or acquired sagacity, aided by knowledge of the particular subject, and 

 of subjects allied with it. Invention, though it can be cultivated, can not 

 be reduced to rule ; there is no science which will enable a man to bethink 

 himself of that which will suit his purpose. 



But when he has thought of something, science can tell him whether 

 that which he has thought of will suit his purpose or not. The inquirer 

 or arguer must be guided by his own knowledge and sagacity in the choice 

 of the inductions out of which he will construct his argument. But the 

 validity of the argument when constructed, depends on principles, and must 

 be tried by tests which are the same for all descriptions of inquiries, 

 whether the result be to give A an estate, or to enrich science with a new 

 general truth. In the one case and in the other, the senses, or testimony, 

 must decide on the individual facts ; the rules of the syllogism will deter- 

 mine whether, those facts being supposed correct, the case really falls with- 

 in the formula? of the different inductions under which it has been succes- 



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