SECTION V.

Of certain misapplications of the words Experience and Induction, in the phraseology of modern science. Illustrations from medicine and from political economy.

In the first section of this chapter, I endeavored to point out the characteristical peculiarities by which the inductive philosophy of the Newtonians is distinguished from the hypothetical systems of their predecessors; and which entitle us to indulge hopes with respect to the permanent stability of their doctrines, which might be regarded as chimerical, if, in anticipating the future history of science, we were to be guided merely by the analogy of its revolutions in the ages that are past.

In order, however, to do complete justice to this argument, as well as to prevent an undue extension of the foregoing conclusions, it is necessary to guard the reader against a vague application of the appropriate terms of inductive science to inquiries which have not been rigorously conducted according to the rules of the inductive logic. From a want of attention to this consideration, there is a danger, on the one hand, of lending to sophistry or to ignorance the authority of those illustrious names whose steps they profess to follow; and, on the other, of bringing discredit on that method of investigation, of which the language and other technical arrangements have been thus perverted.

Among the distinguishing features of the new logic, when considered in contrast with that of the schoolmen, the most prominent is the regard which it professes to pay to experience, as the only solid foundation of human knowledge. It may be worth while, therefore, to consider, how far the notion commonly annexed to this word is definite and precise: and whether there may not sometimes be a possibility of its being employed in a sense more general and loose, than the authors who are looked up to as the great models of inductive investigation understood it to convey."

* As the reflections which follow are entirely of a practical nature, I shall express myself, as far is consistent with a due regard to precision, agreeably to the modes of speaking in common use; without affecting a scrupulous attention to some speculative distinctions, which, however curious and interesting, when considered in connexion with the theory of the mind, do not lead to any logical conclusions of essential importance in the conduct of the understanding. In such sciences for example, as astronomy, natural philosophy, and chemistry, which rest upon phenomena open to the scrutiny of every inquirer, it would obviously be peurile in the extreme to attempt drawing the line between facts which have been ascertained by our own personal observation, and those which we have implicitly adopted upon our faith in the universal consent of the scientific world. The evidence, in both cases, may be equally irresistible; and sometimes the most cautious reasoners may justly be disposed to consider that of testimony as the least fallible of the two.

By far the greater part, indeed, of what is commonly called experimental knowledge, will be found, when traced to its origin, to resolve entirely into our

In the course of the abstract speculations contained in the preceding section, I have remarked, that although the difference between the two sorts of evidence, which are commonly referred to the separate heads of experience and of analogy, be rather a difference in degree than in kind, yet that it is useful to keep these terms in view, in order to mark the contrast between cases which are separated from each other by a very wide and palpable interval; more especially to mark the difference between an argument from individual to individual of the same species, and an argument from species to species of the same genus. As this distinction, however, when accurately examined, turns out to be of a more vague and popular nature than at first sight appears, it is not surprising that instances should occasionally present themselves, in which it is difficult to say, of the evidence before us, to which of these descriptions it ought to be referred. Nor does this doubt lead merely to a question concerning phraseology: it produces a hesitation which must have some effect even on the judgment of a philosopher; the maxims to which we have been accustomed, in the course of our early studies, leading us to magnify the evidence of experience as the sole test of truth; and to depreciate that of analogy, as one of the most fertile sources of error. As these maxims proceed on the supposition, that the respective provinces of both are very precisely defined, it is evident, that, admitting them to be perfectly just in themselves, much danger may still be conceivable from their injudicious application. I shall endeavor to illustrate this remark by some familiar instances; which I trust, will be sufficient to recommend it to the farther consideration of future logicians. To treat of the subject with that minuteness of detail which is suited to its importance, is incompatible with the subordinate place which belongs to it in my general design.

confidence in the judgment and the veracity of our fellow creatures; nor, in the sciences already mentioned, has this identification of the evidence of testimony with that of experience, the slightest tendency to affect the legitimacy of

our inductive conclusions.

In some other branches of knowledge, (more particularly in those political doctrines which assume as incontrovertible data the details of ancient history,) the au thority of testimony is, for obvious reasons, much more questionable; and to dignify it, in these, with the imposing character of experience, is to strengthen one of the chief bulwarks of popular prejudices. This view of the subject, however, although well entitled to the attention of the logician, has no immediate connexion with my present argument; and accordingly I shall make no scruple, in the sequel, to comprehend, under the name of experience, the grounds of our assent to all the facts on which our reasonings proceed, provided only that the certainty of these facts be, on either supposition equally indisputable.

The logical errors which it is the aim of this section to correct, turn upon a still more dangerous latitude in the use of this word: in consequence of which, the authority of experience comes insensibly to be extended to innumerable opinions resting solely on the supposed analogies; while, not unfrequently, the language of Bacon is quoted in bar of any theoretical argument on the other side of the question.

I have added this note, partly to obviate some criticisms, to which my own phraseology may, at first sight, appear liable; and partly to point out the connexion between the following discussion, and some of the foregoing speculations.

It is observed by Dr. Reid, that, "in medicine, physicians must, for the most part, be directed in their prescriptions by analogy. The constitution of one human body is so like that of another, that it is reasonable to think, that what is the cause of health or sickness to one, may have the same effect on another. And this," he adds, "is generally found true, though not without some excep tions."-(Essays on the Intellect. Powers, p. 53.)

I am doubtful if this observation be justified by the common use of language; which, as far as I am able to judge, uniformly refers the evidence on which a cautious physician proceeds, not to analogy, but to experience. The German monk, who, according to the popular tradition, having observed the salutary effects of antimony upon some of the lower animals, ventured to prescribe the use of it to his own fraternity, might be justly said to reason analogically; inasmuch as his experience related to one species, and his inference to another. But if, after having thus poisoned all the monks of his own convent, he had persevered in recommending the same mineral to the monks of another, the example of our most correct writers would have authorized us to say, (how far justly, is a different question,) that he proceeded in direct opposition to the evidence of experience.

In offering this slight criticism on Dr. Reid, I would be very far from being understood to say, that the common phraseology is more unexceptionable than his. I would only remark, that his phraseology on this occasion is almost peculiar to himself and that the prevailing opinions, both of philosophers and of the multitude, incline them to rank the grounds of our reasoning in the medical art, at a much higher point in the scale of evidence than what is marked by the word analogy. Indeed, I should be glad to know, if there be any one branch of human knowledge, in which men are, in general more disposed to boast of the lights of experience than in the practice of medicine.

It would, perhaps, have been better for the world, if the general habits of thinking and of speaking had, in this instance, been more agreeable than they seem to be in fact, to Dr. Reid's ideas; or, at least, if some qualifying epithet had been invariably added to the word experience, to show with how very great latitude it is to be understood, when applied to the evidence on which the physician proceeds in the exercise of his art. The truth is, that, even on the most favorable supposition, this evidence, so far as it rests on experience, is weakened or destroyed by the uncertain conditions of every new case to which his former results are to be applied; and that, without a peculiar sagacity and discrimination in marking, not only the resembling, but the characteristical features of disorders, classed under the same technical name, his practice cannot, with propriety, be said to be guided by any one rational principle of decision, but merely by blind and random conjecture. The more successfully this sagacity and discrimination are exercised, the more

nearly does the evidence of medical practice approach to that of experience; but, in every instance, without exception, so immense is the distance between them, as to render the meaning of the word experience, when applied to medicine, essentially different from its import in those sciences where it is possible for us, in all cases, by due attention to the circumstances of an experiment, to predict its result with an almost infallible certainty.*

Notwithstanding this very obvious consideration, it has become fashionable among a certain class of medical practitioners, since the lustre thrown on the inductive logic of Bacon by the discoveries of Newton and the researches of Boyle, to number their art with the other branches of experimental philosophy; and to speak of the difference between the empiric and the scientific physician, as if it were exactly analogous to that between the cautious experimenter and the hypothetical theorist in physics. Experience, we are told, and experience alone, must be our guide in medicine, as in all the other departments of physical knowledge: nor is any innovation, however rational, proposed in the established routine of practice, but an accumulation of alleged cases is immediately brought forward, as an experimental proof of the dangers which it threatens.

It was a frequent and favorite remark of the late Dr. Cullen, that that there are more false facts current in the world than false theories; and a similar observation occurs, more than once, in the Novun Organon. "Men of learning," says Bacon, in one passage, "are too often led, from indolence or credulity, to avail themselves of mere rumors or whispers of experience, as confirmations, and sometimes as the very groundwork of their philosophy; ascribing to them the same authority as if they rested on legitimate testimony. Like to a government which should regulate its measures, not by the official information received from its own accredited ambassadors, but by the gossipings of newsmongers in the streets. Such, in truth, is the manner in which the interests of philosophy, as far as experience is concerned, have been hitherto administered. Nothing is to be found which has been duly investigated; nothing which has been verified by a careful examination of proofs; nothing

*"L'art de conjecturer en médecine ne sauroit consister dans une suite de raisonnemens appuyés sur un vain système. C'est uniquement l'art de comparer une maladie qu'on doit guérir, avec les maladies semblables qu'on a déja connues par son expérience ou par celle des autres. Cet art consiste méme quelquefois à un rapport entre des maladies qui paroissent n'en point avoir, comme aussi des differences essentielles, quoique fugitives, entre celles qui paroissent se ressembler le plus. Plus on aura rassemblé de faits, plus on sera en état de conjecturer heureusement; supposé néanmoins qu'on ait d'ailleurs cette justesse d'esprit que la nature seule peut donner.

"Ainsi le meilleur médecin n'est pas (comme le préjugé le suppose) celui qui accumule en aveugle et en courant beaucoup de pratique, mais celui qui ne fait que des observations bien approfondies, et qui joint à ces observations le nombre beaucoup plus grand des observations faites dans tous les siecles par des hommes animes du même esprit que lui. Ces observations sont la véritable experience du médecin."-D'Alembert, Eclaircissemens sur les Elémens de Philosophie,

sec. vi.

which has been reduced to the standard of number, weight, or measure."—(Nov. Org. lib. i. Aph. xcviii.)

This very important aphorism deserves the serious attention of those who, while they are perpetually declaiming against the uncertainty and fallacy of systems, are themselves employed in amassing a chaos of insulated particulars, which they admit upon the slenderest evidence. Such men, sensible of their own incapacity for scientific investigation, have often a malicious pleasure in destroying the fabrics of their predecessors; or, if they should be actuated by less unworthy motives, they may yet feel a certain gratification to their vanity, in astonishing the world with anomalous and unlooked for phenomena: a weakness which results not less naturally from ignorance and folly, than a bias to premature generalization from the consciousness of genius. Both of these weaknesses are undoubtedly adverse to the progress of science; but, in the actual state of human knowledge, the former is perhaps the more dangerous of the two.

In the practice of medicine (to which topic I wish to confine myself more particularly at present) there are a variety of other circumstances, which, abstracting from any suspicion of bad faith in those on whose testimony the credibility of facts depends, have a tendency to vitiate the most candid accounts of what is commonly dignified with the title of experience. So deeply rooted in the constitution of the mind is that disposition on which philosophy is grafted, that the simplest narrative of the most illiterate observer involves more or less of hypothesis; nay, in general, it will be found, that in proportion to his ignorance, the greater is the number of conjectural principles involved in his statements.

A village apothecary (and, if possible, in a still greater degree, an experienced nurse) is seldom able to describe the plainest case, without employing a phraseology of which every word is a theory; whereas a simple and genuine specification of the phenomena which mark a particular disease; a specification unsophisticated by fancy, or by preconceived opinions, may be regarded as unequivocal evidence of a mind trained by long and successful study to the most difficult of all arts, that of the faithful interpretation of

nature.

Independently, however, of all these circumstances, which tend so powerfully to vitiate the data whence the physician has to reason; and supposing his assumed facts to be stated, not only with the most scrupulous regard to truth, but with the most jealous exclusion of theoretical expressions, still the evidence upon which he proceeds is, at best, conjectural and dubious, when compared with what is required in chemistry or in mechanics. It is seldom, if ever, possible, that the description of any medical case can include all the circumstances with which the result was connected: and, therefore, how true soever the facts described may be, yet when the conclusion to which they lead comes to be applied as a general