!98 



INBtrCTlON. 



which it is important to conceive 

 correctly. Colligation is not always 

 induction ; but induction is always 

 colligation. The assertion that the 

 planets move in ellipses was but a 

 mode of representing observed facts ; 

 it was but a colligation ; while the 

 assertion that they are drawn or tend 

 towards the sun was the statement of 

 a new fact, inferred by induction. 

 But the induction, once made, accom- 

 plishes the purposes of colligation 

 likewise. It brings the same facts, 

 which Kepler had connected by his 

 conception of an ellipse, under the 

 additional conception of bodies acted 

 upon by a central force, and serves 

 therefore as a new bond of connection 

 for those facts ; a new principle for 

 their classification. 



Further, the descriptions which are 

 improperly confounded with induction 

 are nevertheless a necessary prepara- 

 tion for induction ; no less necessary 

 than correct observation of the facts 

 themselves. Without the previous 

 colligation of detached observations 

 by means of one general conception, 

 we could never have obtained any 

 basis for an induction, except in the 

 case of phenomena of very limited 

 compass. We should not be able to 

 aflirm any predicates at all of a sub- 



his doctrine. He will hardly say that there 

 is 110 contradiction between the emission 

 theory and the undulatory theory of light ; 

 or that there can be both one and two 

 electricities ; or that the hypothesis of 

 the production of the higher organic 

 forms by development from the lower, and 

 the supposition of separate and successive 

 acts of creation, are quite reconcilable ; 

 or that the theory that volcanoes are fed 

 from a central fire, and the doctrines 

 which ascribe them to ciiemical action at 

 a comparatively small depth below the 

 earth's surface, are consistent with one 

 another, and all true as far as they go. 



If different explanations of the same fact 

 cannot both be true, still less, surely, can 

 different predictions. Dr. WheweU quar- 

 rels (on what ground it is not necessary 

 here to consider) with the example I had 

 chosen on this point, and thinks an objec- 

 tion to an illustration a sufl&cient answer 

 to a theory. Examples not liable to his 

 objection are easily found, if the proposi- 

 tion that conflicting predictions cannot 

 both be true can be made clearer by any 



ject incapable of being observed other- 

 wise than piecemeal : much less could 

 we extend those predicates by induc- 

 tion to other similar subjects. Induc- 

 tion, therefore, always presupposes, 

 not only that the necessary observa- 

 tions are made with the necessary 

 accuracy, but also that the results of 

 these observations are, so far as prac- 

 ticable, connected together by general 

 descriptions, enabling the mind to- 

 represent to itself as wholes whatever 

 phenomena are capable of being so 

 represented- 



§ 5. Dr. WheweU has replied at 

 some length to the preceding observa- 

 ;ions, re -stating his opinions, but with- 

 out (as far as I can perceive) adding 

 anything material to his former argu- 

 ments. Since, however, mine have not 

 had the good fortune to make any 

 impression upon him, I will subjoin a 

 few remarks, tending to show more 

 clearly in what our difference of 

 opinion consists, as well as, in some 

 measure, to account for it. 



Nearly all the definitions of induc- 

 tion, by writers of authority, make it 

 consist in drawing inferences from 

 known cases to unknown ; affirming 

 of a class a predicate which has been 

 found true of some cases belonging to 



examples. Suppose the phenomenon to 

 be a newly discovered comet, and that one 

 astronomer predicts its return once in every 

 300 years — another once in every. 400 : can' 

 they both be right ? When Columbus pre- 

 dicted that by sailing constantly westward 

 he should in time return to the point from 

 which he set out, while others asserted that 

 he could never do so except by turning 

 back, were both he and his opponents true 

 prophets ? Were the predictions which fore- 

 told the wonders of railways and steam- 

 ships, and those which averred that the 

 Atlantic could never be crossed by steam 

 navigation, nor a railway train propelled 

 ten miles an hour, both (in Dr. Whewell's 

 words) "true and consistent with one 

 another ? " 



Dr. WheweU sees no distinction between 

 holding contradictory opinions of a ques- 

 tion of fact, and merely employing differ- 

 ent analogies to facilitate the conception 

 of the same fact. The case of different 

 Inductions belongs to the former class, 

 that of diffeient Descriptions to the 

 latter. 



