and it is by reasoning synthetically from the hypothesis, and comparing the deductions with observation and experiment, that the cautious inquirer is gradually led, either to correct it in such a manner as to reconcile it with facts, or finally to abandon it as an unfounded conjecture.-— Even in this latter case, an approach is made to the truth in the way of exclusion; while, at the same time, an accession is gained to that class of associated and kindred phenomena, which it is his object to trace to their parent stock

In thus apologizing for the use of hypotheses, I only repeat in a different form the precepts of Bacon, and the comments of some of his most enlightened followers. The prejudice against hypotheses "which many people entertain, (says the late Dr. Gregory) is founded <? on the equivocal signification of a word. It is commonly confound. "ed with theory-but a hypothesis properly means the supposition of a principle, of whose existence the e is no proof from experience, "but which may be rendered more or less probable by facts which are "neither numerous enough, nor adequate to infer its existence. When "such hypotheses are proposed in the modest and diffident manner that "becomes mere suppositions or conjectures, they are not only barinless, "but even necessary for establishing a just theory. They are the first "rudiments or anticipations of Principles Without these, there could "not be useful observation, nor experiment, nor arrangement, because "there could be no motive or principle in the mind to form them. Hy"potheses then only become dangerous and censurable, when they are "imposed on us for just principles; because, in that case, they put a 66 stop to further inquiry, by leading the mind to acquiesce in principles "which may as probably be ill as well founded."+

Another eminent writer has apologized very ingeniously, and I think very philosophically, for the hypotheses and conjectures which are occasionally to be found in his own works. The author I mean is Dr. Stephen Hales, who, in the preface to the second volume of his Vegetable Statics, has expressed himself thus:

"In natural philosophy, we cannot depend on any mere speculations "of the mind; we can only reason with any tolerable certainty from 66 proper data, such as arise from the united testimony of many good "and credible experiments.

"Yet it seems not unreasonable, on the other hand, though not far to "indulge, to carry our reasonings a little farther than the plain evidence "of experiments will warrant; for since at the utmost boundaries of "those things which we clearly know, a kind of twilight is cast on the "adjoining borders of Terra Incognita, it seems reasonable, in some de"gree, to indulge conjecture there; otherwise we should make but very slow advances, either by experiments or reasoning. For new ex

"Illud interim monemus; ut nemo animo concidat, aut quasi confundatur, si experimenta, quibus incumbit, expectationi suae non respondeant. Etenim quod succedit, magis complaceat; at quod non succedit, saepenumero non minus in. format. Atque illud semper in animo tenendum, experimenta lucifera etiam adhuc magis, quam fructifera ambienda esse. Atque de literata experientia haec dicta sint; quae sagacitas potius est, et odoratio quaedam venatica, quam scientia." De Augm. Scient. Lib. v. Cap. ii.

† Lectures on the Duties and the Qualifications of a Physician.

periments and discoveries usually owe their first rise only to lucky gues d ses and probable conjectures; and even disappointments in these con"jectures often lead to the thing sought for."

To these quotations I shall add two short extracts from Dr. Hooke (the contemporary or rather the predecessor of Newton,) whose acute and original remarks on this subject reflect the greater credit on his talents, that they were published at a period, when the learned body of which he was so illustrious an ornament, seem plainly to have been more disposed to follow the letter of some detached sentences, than to imbibe the general spirit of Bacon's logic.

"There may be use of method in the collecting of materials, as well "as in the employment of them; for there ought to be some end and "aim, some predesigned module and theory; some purpose in our ex"periments. And though this Society have hitherto seemed to avoid "and prohibit preconceived theories and deductions from particular "and seemingly accidental experiments; yet I humbly conceive, that "such, if knowingly and judiciously made, are matters of the greatest "importance; as giving a characteristic of the aim, use, and significa"tion thereof; and without which, many, and possibly the most consid"erable particulars, are passed over without regard and observation." "Where the data on which our ratiocinations are founded are uncer❝tain and only conjectural, the conclusions or deductions therefrom "can at best be no other than probable, but still they become more and "more probable, as the consequences deduced from them appear, upon "examinations by trials and designed observations to be confirmed by "fact or effect. So that the effect is that which consummates the demon"stration of the invention: and the theory is only an assistant to direct "such an inquisition, as may procure the demonstration of its existence "or uon-existence t

As an illustration of this last remark, Hooke mentions his anticipation of Jupiter's motion upon his axis, long before he was able by means of a good telescope, to ascertain the fact. A much more remarkable instance, however, of his philosophical sagarity, occurs in his anticipation of that theory of the planetary motions, which, soon after, was to present itself, with increased and at length demonstrative evidence, to a still more inventive and powerful mind. This conjecture (which I shall state in his own words,) affords, of itself, a decisive reply to the undistinguishing censures which have so often been bestowed on the presumptuous vanity of attempting, by means of hypotheses, to penetrate into the secrets of nature.

"I will explain (says Hooke, in a communication to the Royal Socie"ty in 1666) a system of the world very different from any yet received. "It is founded on the three following positions.

"1. That all the heavenly bodies have not only a gravitation of their parts to their own proper centre, but that they also mutually attract "each other within their spheres of action.

'

"2. That all bodies having a simple motion, will continue to move in a straight line, unless continually deflected from it by some extraneous

* Hooke's Posthumous Works, p. 280..

Ibid. p. 537. For another extract from the same work, see note (S.)

"force, causing them to describe a circle, an ellipse, or some other

❝ curve.

cr

"3. That this attraction is so much the greater as the bodies are nearer. As to the proportion in which those forces diminish by an "increase of distance, I own I have not discovered it, although I have "made some experiments to this purpose. I leave this to others, who "have time and knowledge sufficient for the task."

The argument in favour of Hypotheses might be pushed much farther, by considering the tentative or hypothetical steps by which the most cautious philosophers are often under the necessity of proceeding, in conducting inquiries strictly experimental. These cannot be better described than in the words of Boscovich, the slightest of whose logical hints are entitled to peculiar attention." In some instances, observations and "experiments at once reveal to us all that we wish to know. In other cases, we avail ourselves of the aid of hypotheses;—by which word, "however, is to be understood, not fictions altogether arbitrary, but suppo"sitions conformable to experience or to analogy By means of these, "we are enabled to supply the defects of our data, and to conjecture or "divine the path to truth; always ready to abandon our hypothesis, "when found to involve consequences inconsistent with fact. And in"deed, in most cases, I conceive this to be the method best adapted to "physics; a science, in which the procedure of the inquirer may be "compared to that of a person attempting to decypher a letter written " in a secret character; and in which, legitin ate theories are generally "the slow result of disappointed essays, and of errors which have led "the way to their own detection.'

De Solis ac Lunae Defectibus. Lond. 1760. pp. 211, 212. For the continuation of the above passage, see note (T)

Many remarks to the same purpose may be found in Bacon. The following hap pen at present to occur to my memory.

"Deo (formarum inditori et opifici) et fortasse angelis, competit, formas per affirmationem immediate nosse, atque ab initio contemplationis. Sed certe supra hominem est; cui tantum conceditur, procedere primo per negativas, et postremo loco desinere in affirmativas, post omnimodam exclusionem. Post rejectionem et exclusionem debitis modis factam, secundo loco (tanquam infundo) menebit (abeuntibus in fumum opinionibus volatilibus) forma affirmativa, solida, et vera. Atque hoc brevi dictu est, sed per multas ambages ad-hoc pervenitur." (Nov Org. Lib. II. Aphor XV. XVI.)

"Prudens interrogatio quasi dimidium scientiae. Idcirco quo amplior et certior fuerit anticipatio nostra; eo magis directa et compendiosa erit investigatio." (De Aug Scient. Lib. V. Cap. 3.

66

Vaga experientia, et se tantum sequens, mera palpatio est, et homines potius stupefacit, quam informat." (Nov. O g. Lib. I. Aphor. C.)

The reader who wishes to prosecute farther this speculation concerning the use of hypotheses, may consult with advantage three short but interesting memoirs up. on Method, by the late M. Le Sage, of Geneva, which M. Prevost has annexed as a supplement to his Essais de Philosophie. That I may not be supposed, however, to acquiesce in all this author's views, I shall mention two strong objections to which some of them appear to me to be liable.

1. In treating of the method of Hypothesis, Le Sage uniformly contrasts it with that of Analogy. as if the two were radically distinct, and even opposite in their spirit; whereas it seems evident, that some perception of analogy must have given birth to every hypothesis which possesses a sufficient degree of plausibility to deserve farther examination.

2. In applying the rules of Mathematical Method to Physics, he makes far too little allowance for the essential difference between the two sciences. This is

Nor is it solely by the erroneous results of his own hypotheses, that the philosopher is assisted in the investigation of truth. Similar lights are often to be collected from the errors of his predecessors; and hence it is, that accurate histories of the different sciences may justly be ranked among the most effectual means of accelerating their future advancement. It was from a review of the endless and hopeless wanderings of preceding inquirers, that Bacon inferred the necessity of avoiding every beaten track; and it was this which encouraged bim,— with a confidence in his own powers amply justified by the event-to explore and to open a new path to the mysteries of nature: Inveniam viam, aut faciam. In this respect, the maturity of reason in the species is analogous to that in the individual; not the consequence of any sudden or accidental cause, but the fruit of reiterated disappointments correcting the mistakes of youth and inexperience. "There is no subject "(says Fontenelle) on which men ever come to form a reasonable opinion, "till they have once exhausted all the absurd views which it is possible "to take of it. What follies (be adds) should we not be repeating at "this day, if we had not been anticipated in so many of them by the "ancient philosophers!"-Those systems, therefore, which are false, are by no means to be regarded as altogether useless. That of Ptolemy (for example) as Bailly has well observed, is founded on a prejudice so natural and so unavoidable, that it may be considered as a necessary step in the progress of astronomical science; and if it had not been proposed in ancient times, it would infallibly have preceded, among the moderns, the system of Copernicus, and retarded the period of its discovery.

In what I have hitherto said in defence of the method of Hypothesis, I have confined myself entirely to its utility as an organ of investigation; taking all along for granted, that, till the principle assumed has been fairly inferred as a law of nature, from undoubted facts, none of the explanations which it affords are to be admitted as legitimate theories. Some of the advocates for this method have however gone much farther; asserting, that if a hypothesis be sufficient to account for all the phenomena in question, no other proof of its conformity to truth is necessary. "Supposing (says Dr. Hartley) the existence of the aether to be destitute "of all direct evidence, still, if it serves to explain and account for a "great variety of phenomena, it will, by this means, have an indirect ar"gument in its favour. Thus, we admit the key of a cypher to be a true "one, when it explains the cypher completely; and the decypherer "judges himself to approach to the true key, in proportion as he ad"vances in the explanation of the cypher; and this without any direct "evidence at all "* On another occasion, he observes, that Philoso❝phy is the art of decyphering the mysteries of nature; and that every "theory which can explain all the phenomena, has the same evidence "in its favour, that it is possible the key of a cypher can have from its explaining that cypher."+

more particularly remarkable in his observations on the aid to be derived, in investigating the laws of nature, from the methods of Exclusions,—so happily employed by Frenicle de Bessy (a French mathematician of the 17th century) in the solution of some very difficult problems relating to numbers.—See note (U.)

Observations on Man, Vol. I. pp. 15, 16, (4th edit.)

† Ibid. p. 350. The section from which this quotation is taken, entitled "Of

OF THE HUMAN MIND.

213

The same very ingenious and plausible reasoning is urged by Le Sage in one of his posthumous fragments; and, long before the publication of Hartley's work, it had struck Gravesande so strongly, that, in his Introductio ad Philosophiam, he has subjoined to his chapter on the Use of Hypotheses, another on the Art of Decyphering. Of the merit of the latter it is no slight proof, that D'Alembert has inserted the substance of it in one of the articles of the Encyclopedia.tayboy

In reply to Hartley's comparison between the business of the philo sopher and that of the decypherer, Dr. Reid observes, that to find the "key requires an understanding equal or superior to that which made "the cypher. This instance, therefore, (he adds,) will then be in point, "when he who attempts to decypher the works of nature by a hypothe"sis, has an understanding equal or superior to that which made them." The argument is not stated with the author's usual correctness in point of logic; in as much as the first proposition contrasts the sagacity of the decypherer with that of the contriver of the cypher; and the second, with that of the author of the composition decyphered. Nor is this all. The argument proceeds on the supposition, that, if the task of the scientific inquirer be compared to that of the decypherer, the views of the author of nature may, with equal propriety, be compared to those of the inventor of the cypher. It is impossible to imagine that this was Hartley's idea. The object of true philosophy is, in no case, presumptuously to divine an alphabet of secret characters or cyphers, purposely employed by infinite Wisdom to conceal its operations; but, by the diligent study of facts and analogies legible to all, to discover the key whirh infinite wisdom has itself prepared for the interpretation of its own laws. In other words, its object is, to concentrate and to cast on the unknown parts of the universe, the lights which are reflected from those which are known.

In this instance, as well as in others, where Reid reprobates hypotheses, his reasoning uniformly takes for granted, that they are wholly arbitrary and gratuitous. If a thousand of the greatest wits (says he) "that ever the world produced, were without any previous knowledge in "anatomy, to sit down and contrive how, and by what internal organs, "the various functions of the human body are carried on-how the "blood is made to circulate, and the limbs to move--they would not, in "a thousand years, hit upon any thing like the truth Nothing can

Propositions and the nature of Assent," contains various ingenious and just observations, blended with others strongly marked with the author's peculiar turn of thinking. Among these last may be mentioned his Theory of Mathematical Evidence, coinciding exactly with that which has since been proposed by Dr. Beddoes. Compare Hartley with pp. 138, 139 of this volume.

"N'admettons-nous pas pour vraie, la clef d'une lettre écrite en chiffres, ou celle d'un logogriphe; quand cette clef s'applique exactement à tous les carac tères dont il faut rendre raison" Opuscules de G. L. Le Sage, relatifs à la Métbode. See M. Prévost's Essais de Philosophie.

Article Déchiffrer. See also D'Alembert's Oeuvres Posthumes. Tome II. p. 177.-Gravesande's Logic was published in 1736.

+ Essays on the Intell. Powers, p. 88.

§ Ibid. p. 49.