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CHAPTER III: Of the Ground of Induction - John Stuart Mill, The Collected Works of John Stuart Mill, Volume VII - A System of Logic Ratiocinative and Inductive [1843]Edition used:The Collected Works of John Stuart Mill, Volume VII - A System of Logic Ratiocinative and Inductive, Being a Connected View of the Principles of Evidence and the Methods of Scientific Investigation (Books I-III), ed. John M. Robson, Introduction by R.F. McRae (Toronto: University of Toronto Press, London: Routledge and Kegan Paul, 1974).
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CHAPTER IIIOf the Ground of Induction§ 1. [Axiom of the uniformity of the course of nature] Induction properly so called, as distinguished from those mental operations, sometimes though improperly designated by the name, which I have attempted in the preceding chapter to characterize, may, then, be summarily defined as Generalization from Experience. It consists in inferring from some individual instances in which a phenomenon is observed to occur, that it occurs in all instances of a certain class; namely, in all which resemble the former, in what are regarded as the material circumstances. In what way the material circumstances are to be distinguished from those which are immaterial, or why some of the circumstances are material and others not so, we are not yet ready to point out. We must first observe, that there is a principle implied in the very statement of what Induction is; an assumption with regard to the course of nature and the order of the universe; namely, that there are such things in nature as parallel cases; that what happens once, will, under a sufficient degree of similarity of circumstances, happen again, and not only again, but aas often as the same circumstances recura . This, I say, is an assumption, involved in every case of induction. And, if we consult the actual course of nature, we find that the assumption is warrantedb . The universe, cso far as known to usc , is so constituted, that whatever is true in any one case, is true in all cases of a certain description; the only difficulty is, to find what description. This universal fact, which is our warrant for all dinferencesd from experience, has been described by different philosophers in different forms of language: that the course of nature is uniform; that the universe is governed by general laws; and the like. One of the most usual of these modes of expression, but also one of the most inadequate, is that which has been brought into familiar use by the metaphysicians of the school of Reid and Stewart. The disposition of the human mind to generalize from experience,—a propensity considered by these philosophers as an instinct of our nature,—they usually describe under esome such name ase “our intuitive conviction that the future will resemble the past.” Now it has been well pointed out fby Mr. Bailey* thatf (whether the tendency be or not an original and ultimate element of our nature), Time, in its modifications of past, present, and future, has no concern either with the belief itself, or with the grounds of it. We believe that fire will burn to-morrow, because it burned to-day and yesterday; but we believe, on precisely the same grounds, that it burned before we were born, and that it burns this very day in Cochin-China. It is not from the past to the future, as past and future, that we infer, but from the known to the unknown; from facts observed to facts unobserved; from what we have perceived, or been directly conscious of, to what has not come within our experience. In this last predicament is the whole region of the future; but also the vastly greater portion of the present and of the past. Whatever be the most proper mode of expressing it, the proposition that the course of nature is uniform, is the fundamental principle, or general axiom, of Induction. It would yet be a great error to offer this large generalization as any explanation of the inductive process. On the contrary, I hold it to be itself an instance of induction, and induction by no means of the most obvious kind. Far from being the first induction we make, it is one of the last, or at all events one of those which are latest in attaining strict philosophical accuracy. As a general maxim, indeed, it has scarcely entered into the minds of any but philosophers; nor even by them, as we shall have many opportunities of remarking, have its extent and limits been always very justly conceived. gThe truth is, that this great generalization is itself founded on prior generalizations. The obscurer laws of nature were discovered by means of it, but the more obvious ones must have been understood and assented to as general truths before it was ever heard of. We should never have thought of affirming that all phenomena take place according to general laws, if we had not first arrived, in the case of a great multitude of phenomena, at some knowledge of the laws themselves; which could be done no otherwise than by induction. In what sense, then, can a principle, which is so far from being our earliest induction, be regarded as our warrant for all the others? In the only sense, in which (as we have already seen)g the general propositions which we place at the head of our reasonings when we throw them into syllogisms, ever really contribute to their validity. hAs Archbishop Whately remarks,h[*] every induction is a syllogism with the major premise suppressed; or (as I prefer expressing it) i every induction may be thrown into the form of a syllogism, by supplying a major premise. If this be actually done, the principle which we are now considering, that of the uniformity of the course of nature, will appear as the ultimate major premise of all inductions, and will, therefore, stand to all inductions in the relation in which, as has been shown at so much length, the major proposition of a syllogism always stands to the conclusion; not contributing at all to prove it, but being a necessary condition of its being proved; since no conclusion is proved, for which there cannot be found a true major premise.* lThe statement, that the uniformity of the course of nature is the ultimate major premise in all cases of induction, may be thought to require some explanation. The immediate major premise in every inductive argument, it certainly is not. Of that, Archbishop Whately’s must be held to be the correct account.mThe induction, “John, Peter,n &c. are mortal, therefore all mankind are mortal,” may, as he justly says, be thrown into a syllogism by prefixing as a major premise (what is at any rate a necessary condition of the validity of the argument) namely, that owhat is true of John, Peter,o &c. is true of all mankind.m But pqhow came we by thisq major premise? It is not self-evident; nay, in all cases of unwarranted generalization, it is not true. How, then, is it arrived at? Necessarily either by induction or ratiocination; and if by induction,p the process, like all other inductive arguments, may be thrown into the form of a syllogism. rThis previous syllogism it is, therefore, necessary to construct. There is, in the long run, only one possible construction. The real proof thatswhats is true of John, Peter, &c. is true of all mankind, can only be, that a different supposition would be inconsistent with the uniformity which we know to exist in the course of nature. Whether there would be this inconsistency or not, may be a matter of long and delicate inquiry; but unless there would, we have no sufficient ground for the major of the inductive syllogism. It hence appears, that if we throw the whole course of any inductive argument into a series of syllogisms, we shall arrive by more or fewer steps at an ultimate syllogism, which will have for its major premise the principle, or axiom, of the uniformity of the course of nature.rl* It was not to be expected that in the case of this axiom, any more than of other axioms, there should be unanimity among uthinkersu with respect to the grounds on which it is to be received as true. I have already stated that I regard it as itself a generalization from experience. Others hold it to be a principle which, antecedently to any verification by experience, we are compelled by the constitution of our thinking faculty to assume as true. Having so recently, and at so much length, combated a similar doctrine as applied to the axioms of mathematics, by arguments which are in a great measure applicable to the present case, I shall defer the more particular discussion of this controverted point in regard to the fundamental axiom of induction, until a more advanced period of our inquiry.* At present it is of more importance to understand thoroughly the import of the axiom itself. For the proposition, that the course of nature is uniform, possesses rather the brevity suitable to popular, than the precision requisite in philosophical language: its terms require to be explained, and a stricter than their ordinary signification given to them, before the truth of the assertion can be admitted. § 2. [Axiom of the uniformity of nature not true in every sense. Induction per enumerationem simplicem] Every person’s consciousness assures him that he does not always expect uniformity in the course of events; he does not always believe that the unknown will be similar to the known, that the future will resemble the past. Nobody believes that the succession of rain and fine weather will be the same in every future year as in the present. Nobody expects to have the same dreams repeated every night. On the contrary, everybody mentions it as something extraordinary, if the course of nature is constant, and resembles itself, in these particulars. To look for constancy where constancy is not to be expected, as for instance that a day which has once brought good fortune will always be a fortunate day, is justly accounted superstition. The course of nature, in truth, is not only uniform, it is also infinitely various. Some phenomena are always seen to recur in the very same combinations in which we met with them at first; others seem altogether capricious; while some, which we had been accustomed to regard as bound down exclusively to a particular set of combinations, we unexpectedly find detached from some of the elements with which we had hitherto found them conjoined, and united to others of quite a contrary description. To an inhabitant of Central Africa, fifty years ago, no fact probably appeared to rest on more uniform experience than this, that all human beings are black. To Europeans, not many years ago, the proposition, All swans are white, appeared an equally unequivocal instance of uniformity in the course of nature. Further experience has proved to both that they were mistaken; but they had to wait fifty centuries for this experience. During that long time, mankind believed in an uniformity of the course of nature where no such uniformity really existed. According to the notion which the ancients entertained of induction, the foregoing were cases of as legitimate inference as any inductions whatever. In these two instances, in which, the conclusion being false, the ground of inference must have been insufficient, there was, nevertheless, as much ground for it as this conception of induction admitted of. The induction of the ancients has been well described by Bacon, under the name of “Inductio per enumerationem simplicem, ubi non reperitur instantia contradictoria.”[*] It consists in ascribing the character of general truths to all propositions which are true in every instance that we happen to know of. This is the kind of induction a which is natural to the mind when unaccustomed to scientific methods. The tendency, which some call an instinct, and which others account for by association, to infer the future from the past, the known from the unknown, is simply a habit of expecting that what has been found true once or several times, and never yet found false, will be found true again. Whether the instances are few or many, conclusive or inconclusive, does not much affect the matter: these are considerations which occur only on reflection; the unprompted tendency of the mind is to generalize its experience, provided this points all in one direction; provided no other experience of a conflicting character comes unsought. The notion of seeking it, of experimenting for it, of interrogating nature (to use Bacon’s expression)[†] is of much later growth. The observation of nature, by uncultivated intellects, is purely passive: they bacceptb the facts which present themselves, without taking the trouble of searching for more: it is a superior mind only which asks itself what facts are needed to enable it to come to a csafec conclusion, and then looks out for these. But though we have always a propensity to generalize from unvarying experience, we are not always warranted in doing so. Before we can be at liberty to conclude that something is universally true because we have never known an instance to the contrary, dwe must have reason to believed that if there were in nature any instances to the contrary, we should have known of them. This assurance, in the great majority of cases, we cannot have, or can have only in a very moderate degree. The possibility of having it, is the foundation on which we shall see hereafter that induction by simple enumeration may in some remarkable cases amount epractically toe proof.* No such assurance, however, can be had, on any of the ordinary subjects of scientific inquiry. Popular notions are usually founded on induction by simple enumeration; in science it carries us but a little way. We are forced to begin with it; we must often rely on it provisionally, in the absence of means of more searching investigation. But, for the accurate study of nature, we require a surer and a more potent instrument. It was, above all, by pointing out the insufficiency of this rude and loose conception of Induction, that Bacon merited the title so generally awarded to him, of Founder of the Inductive Philosophy. The value of his own contributions to a more philosophical theory of the subject has certainly been exaggerated. Although (along with some fundamental errors) his writings contain, more or less fully developed, several of the most important principles of the Inductive Method, physical investigation has now far outgrown the Baconian conception of Induction. Moral and political inquiry, indeed, are as yet far behind that conception. The current and approved modes of reasoning on these subjects are still of the same vicious description against which Bacon protested; the method almost exclusively employed by those professing to treat such matters inductively, is the very inductio per enumerationem simplicem which he condemns; and the experience which we hear so confidently appealed to by all sects, parties, and interests, is still, in his own emphatic words, mera palpatio.[*] § 3. [The question of Inductive Logic stated] In order to a better understanding of the problem which the logician must solve if he would establish a scientific theory of Induction, let us compare a few cases of incorrect inductions with others which are acknowledged to be legitimate. Some, we know, which were believed for centuries to be correct, were nevertheless incorrect. That all swans are white, cannot have been a good induction, since the conclusion has turned out erroneous. The experience, however, on which the conclusion rested, was genuine. From the earliest records, the testimony of a the inhabitants of the known world was unanimous on the point. The uniform experience, therefore, of the inhabitants of the known world, agreeing in a common result, without one known instance of deviation from that result, is not always sufficient to establish a general conclusion. But let us now turn to an instance apparently not very dissimilar to this. Mankind were wrong, it seems, in concluding that all swans were white: are we also wrong, when we conclude that all men’s heads grow above their shoulders, and never below, in spite of the conflicting testimony of the naturalist Pliny?[†] As there were black swans, though civilized bpeopleb had existed for three thousand years on the earth without meeting with them, may there not also be “men whose heads do grow beneath their shoulders,”[*] notwithstanding a rather less perfect unanimity of negative testimony from c observers? Most persons would answer No; it was more credible that a bird should vary in its colour, than that dmen should vary in the relative position of theird principal organs. And there is no doubt that in so saying they would be right: but to say why they are right, would be impossible, without entering more deeply than is usually done, into the true theory of Induction. Again, there are cases in which we reckon with the most unfailing confidence upon uniformity, and other cases in which we do not count upon it at all. In some we feel complete assurance that the future will resemble the past, the unknown be precisely similar to the known. In others, however invariable may be the result obtained from the instances which ehave beene observed, we draw from them no more than a very feeble presumption that the like result will hold in all other cases. That a straight line is the shortest distance between two points, we do not doubt to be true even in the region of the fixed stars.* When a chemist announces the existence and properties of a newly-discovered substance, if we confide in his accuracy, we feel assured that the conclusions he has arrived at will hold universally, though the induction be founded but on a single instance. We do not withhold our assent, waiting for a repetition of the experiment; or if we do, it is from a doubt whether the one experiment was properly made, not whether if properly made it would be conclusive. Here, then, is a general law of nature, inferred without hesitation from a single instance; an universal proposition from a singular one. Now mark another case, and contrast it with this. Not all the instances which have been observed since the beginning of the world, in support of the general proposition that all crows are black, would be deemed a sufficient presumption of the truth of the proposition, to outweigh the testimony of one unexceptionable witness who should affirm that in some region of the earth not fully explored, he had caught and examined a crow, and had found it to be grey. Why is a single instance, in some cases, sufficient for a complete induction, while in others, myriads of concurring instances, without a single exception known or presumed, go such a very little way towards establishing an universal proposition? Whoever can answer this question knows more of the philosophy of logic than the wisest of the ancients, and has solved the f problem of induction. [a-a]MS, 43, 46 always [b]MS, 43, 46 ; the fact is so [c-c]MS, 43, 46, 51 we find [d-d]MS, 43, 46 inference [e-e]MS, 43, 46 the name of [f-f]MS by a deservedly popular writer,* that [footnote: *Mr. Samuel Bailey, in his Essays on the Pursuit of Truth. 51, 56 , that [i.e., reference to Bailey and footnote deleted]]] [* ]Essays on the Pursuit of Truth [London: Hunter, 1829]. [g-g]MS, 43, 46 Yet this principle, though so far from being our earliest induction, must be considered as our warrant for all the others, in this sense, that unless it were true, all other inductions would be fallacious. And this, as we have already seen, is the sole mode in which [h-h]MS, 43 Archbishop Whately has well remarked, that [[*] ]Elements of Logic, p. 233. [i]MS, 43 that [* ][62] jIn the first edition a note was appended at this place, containing some criticism on Archbishop Whately’s mode of conceiving the relation between Syllogism and Induction. In a subsequent issue of his Logic, the Archbishop made a reply to the criticism, which induced me to cancel part of the note, incorporating the remainder in the text. In a still later edition, the Archbishop observes in a tone of something like disapprobation, that the objections, “doubtless from their being fully answered and found untenable, were silently suppressed,” and that hence he might appear to some of his readers to be combating a shadow. On this latter point, the Archbishop need give himself no uneasiness. His readers, I make bold to say, will fully credit his mere affirmation that the objections have actually been made. [l-l]310+51, 56, 62, 65, 68, 72 [MS, 43, 46 partly in note; see following variants] [m-m]MS, 43, 46 [in footnote; see 308j-j] [n]MS, 43, 46 Thomas, [in footnote; see 308j-j] [o-o]MS, 43, 46 whatever is true of John, Peter, Thomas, [in footnote; see 308j-j] [p-p]MS, 43, 46 [in footnote; see 308j-j] [q-q]MS, 43, 46 How we come by the [in footnote; see 308j-j] ] 51, 56, 62 how come we by this [r-r]MS, 43, 46 [in footnote; see 308j-j] [s-s]MS, 43, 46 whatever [in footnote; see 308j-j] [* ][51] But though it is a condition of the validity of every induction that there be uniformity in the course of nature, it is not a necessary condition that the uniformity should pervade all nature. It is enough that it pervades the particular class of phenomena to which the induction relates. An induction concerning the motions of the planets, or the properties of the magnet, would not be vitiated though we were to suppose that wind and weather are the sport of chance, provided it be assumed that astronomical and magnetic phenomena are under the dominion of general laws. Otherwise the early experience of mankind would have rested on a very weak foundation; for in the infancy of science it could not be t known that all phenomena are regular in their course. [u-u]MS, 43, 46 philosophers [* ]Infra, Chap. xxi [pp. 562ff.]. [[*] ]See De Augmentis, p. 620; cf. Novum Organum, Bk. I, Aph. 105, p. 205. [a]MS, 43, 46 , if it deserves the name, [[†] ]See, e.g., De Augmentis, p. 635. [b-b]MS, 43 take [c-c]MS, 43, 46, 51, 56, 62 sure [d-d]MS, 43, 46 it must be proved to us [e-e]MS, 43, 46 to full [* ][43] Infra, Chaps. xxi, xxii [pp. 562ff.]. [[*] ]Novum Organum, Bk. I, Aph. 82, p. 189. [a]MS, 43, 46 all [[†] ]Natural History. Ed. H. Rackham. 10 vols. London: Heinemann, 1938-1942, Vol. II, p. 520 (Bk. VII, Chap. ii). [b-b]MS, 43, 46 men [[*] ]William Shakespeare. Othello (ed. Furness), I, iii, 167-8. [c]MS, 43, 46 all [d-d]MS, 43, 46 man should . . . of his [e-e]MS, 43, 46 we have [* ][72] In strictness, wherever the present constitution of space exists; which we have ample reason to believe that it does in the region of the fixed stars. [f]MS, 43, 46 great [* ][62] jIn the first edition a note was appended at this place, containing some criticism on Archbishop Whately’s mode of conceiving the relation between Syllogism and Induction. In a subsequent issue of his Logic, the Archbishop made a reply to the criticism, which induced me to cancel part of the note, incorporating the remainder in the text. In a still later edition, the Archbishop observes in a tone of something like disapprobation, that the objections, “doubtless from their being fully answered and found untenable, were silently suppressed,” and that hence he might appear to some of his readers to be combating a shadow. On this latter point, the Archbishop need give himself no uneasiness. His readers, I make bold to say, will fully credit his mere affirmation that the objections have actually been made. [* ][51] But though it is a condition of the validity of every induction that there be uniformity in the course of nature, it is not a necessary condition that the uniformity should pervade all nature. It is enough that it pervades the particular class of phenomena to which the induction relates. An induction concerning the motions of the planets, or the properties of the magnet, would not be vitiated though we were to suppose that wind and weather are the sport of chance, provided it be assumed that astronomical and magnetic phenomena are under the dominion of general laws. Otherwise the early experience of mankind would have rested on a very weak foundation; for in the infancy of science it could not be t known that all phenomena are regular in their course. [jIn the first edition a note was appended at this place, containing some criticism on Archbishop Whately’s mode of conceiving the relation between Syllogism and Induction. In a subsequent issue of his Logic, the Archbishop made a reply to the criticism, which induced me to cancel part of the note, incorporating the remainder in the text. In a still later edition, the Archbishop observes in a tone of something like disapprobation, that the objections, “doubtless from their being fully answered and found untenable, were silently suppressed,” and that hence he might appear to some of his readers to be combating a shadow. On this latter point, the Archbishop need give himself no uneasiness. His readers, I make bold to say, will fully credit his mere affirmation that the objections have actually been made.]MS From the fact, that every induction may be expressed in the form of a syllogism, Archbishop Whately concludes that Induction itself is but a peculiar case of ratiocination, and that the universal type of all Inference, or Reasoning, is the Syllogism. Our own inquiries have led us to a directly opposite result. Instead of resolving Induction into Ratiocination, it has appeared to us that Ratiocination is itself resolvable into Induction. The Archbishop’s theory, may, I think, be shown to be fallacious by following out his own train of thought. The induction, “John, Peter, Thomas, &c., are mortal, therefore all mankind are mortal,” may, as he justly says, be thrown into a syllogism by prefixing as a major premiss (what is at any rate a necessary condition of the validity of the argument) namely, that whatever is true of John, Peter, Thomas, &c., is true of all mankind. So far the case is made out; and Archbishop Whately (who, endowed with a penetrating and active rather than a patient and persevering intellect, seldom fails to cast his sounding line to a greater depth than his predecessors, and when he has done this, scarcely seems to care whether he reaches the bottom or not) omitted to ask himself the further question, How we come by the major premiss? It is not self-evident; nay, in all cases of unwarranted generalization, it is not true. How, then, is it arrived at? Necessarily either by induction or ratiocination; and if by induction, then, on the Archbishop’s principles, it is by ratiocination still, that is, by a previous syllogism. This previous syllogism it is, therefore, necessary to construct. There is, in the long run, only one possible construction: the real proof that whatever is true of John, Peter, &c., is true of all mankind, can only be, that a different supposition would be inconsistent with the uniformity which we know to exist in the course of nature. Whether there would be this inconsistency or not, may be a matter of long and delicate inquiry; but unless there would, we have no sufficient ground for the major of the inductive syllogism. It hence appears, that if we throw the whole course of any inductive argument into a series of syllogisms, we shall arrive by more or fewer steps at an ultimate syllogism, which will have for its major premiss the principle, or axiom, of the uniformity of the course of nature. Having reached this point, we have the whole field of induction laid out in syllogisms, and every instance of inference from experience exhibited as the conclusion of a ratiocination, except one; but that one, unhappily, includes all the rest. Whence came the universal major? What proves to us that nature is governed by general laws? Where are the premisses of the syllogism of which that is the conclusion? Here, at least, is a case of induction which cannot be resolved into syllogism. And undoubtedly it would be the ideal perfection of Inductive Philosophy if all other general truths could be exhibited as conclusions deduced from that widest generalization of all. But such a mode of presenting them, however useful in giving coherence and systematic unity to our thoughts, would be an inversion of the real order of proof. This great generalization must itself have been founded on prior generalizations: the obscurer laws of nature were discovered by means of it, but the more obvious ones must have been understood and assented to as general truths before it was ever heard of. We should never have dared to affirm that all phenomena take place according to general laws, if we had not first arrived, in the case of a great multitude of phenomena, at some knowledge of the laws themselves; which could be done no otherwise than by induction. Archbishop Whately’s theory, therefore, implying, as it does, the consequence that we never could have had a single well-grounded induction unless we had already reached that highest generalization, must, I conceive, be regarded as untenable.] 43 as MS . . . into syllogism. [paragraph] And undoubtedly . . . as MS] 46 as MS . . . then, on his principles, it is . . . as 43 . . . We should never have presumed to . . . as MS] 51, 56 [no footnote] [kfalls intok]62, 65, 68 commits [t]51 said to be |

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