INDUCTION IN GENERAL. 173 



business, such for instance as the advocate or the judge, the chief diffi- 

 culty is one in which the principles of induction will aUbrd him no as- 

 sistance. It lies not in mahing his inductions but in the selection of 

 them ; in choosing from among all general propositions ascertained to 

 be true, those which furnish him with 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 prop- 

 ositions or principles to which the advocate appeals are mostly, in them- 

 selves, sufficiently ti-ite, and assented to as soon as stated : his skill lies 

 in bringing his case under those propositions or princij)les ; in calling 

 to mind such of the known or recognized maxims of probability as ad- 

 mit of application to the case in hand, and selecting from among them 

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

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

 and of subjects allied with it. Invention, though it can be cultivated, 

 cannot 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 his 

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

 But the validity of the argument when constructed, depends upon 

 principles and must be tried by tests which are the same for all de- 

 scriptions 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 determine whether, those facts being 

 supposed correct, the case really falls within the formulas of the differ- 

 ent inductions under which it has been successively brought ; and finally, 

 the legitimacy of the inductions themselves must be decided by other 

 rules, and these it is now our purpose to investigate. If this third part 

 of the operation be, in many of the questions of practical life, not the 

 most, but the least arduous portion of it, we have seen that this is also 

 the case in some great departTnents of the field of science ; in all those 

 which are principally deductive, and most of all in mathematics ; where 

 the inductions themselves are few in number, and so obvious and ele- 

 mentary, that they seem to stand in no need of the evidence of experi- 

 ence, while to combine them so as to prove a given theorem or solve a 

 problem, may call for the highest powers of invention and contrivance 

 with which our species is gifted. 



If the identity of the logical processes which prove particular facts 

 and those which establish general scientific ti'uths, required any addi- 

 tional confii-mation, it would be sufficient to consider, that in many 

 branches of science single facts have to be proved, as well as princi- 

 ples ; facts as completely individual as any that are debated in a court 

 of justice ; but which are proved in the same manner as the other 

 truths of the science, and without disturbing in any degree the homo- 

 geneity of its method. A remarkable examjile of this is afforded by 

 astronomy. The individual facts upon which that science gi'ounds 

 its most important deductions, sUch facts as the magnitudes of the 

 bodies of the solar system, their distances fi'om one another, the figure 

 of the earth, and its rotation, are scarcely any of them accessible to 

 our means of direct observation : they are proved indirectly, by the 



