The sole difference is, that he had an opportunity of verifying the results of his conjectures by an appeal to sensible facts: but this accidental circumstance (although it certainly affords peculiar satisfaction and conviction to the astronomer's mind) does not affect the grounds on which the conjecture was originally formed, and only furnishes an experimental proof of the justness of the principles on which it proceeded. Were it not, however, for the palpable confirmation thus obtained of the Theory of Gravity, it would be difficult to vindicate against the charge of presumption, the mathematical accuracy with which the Newtonians pretend to compute the motions, distances, and magnitudes of worlds, apparently so far removed beyond the examination of our faculties.*

The foregoing observations have a close connection with some reasonings hereafter to be offered in defence of the doctrine of final causes. They also throw additional light on what was remarked in a former chapter concerning

*"I know no author (says Dr. Reid) who has made a more just and a more happy use of analogical reasoning, than Bishop Butler, in his analogy of Religion, Natural and Revealed, to the Constitution and Course of Nature. In that excellent work, the author does not ground any of the truths of religion upon Analogy, as their proper evidence. He only makes use of Analogy to answer objections against them. When objections are made against the truths of religion, which may be made with equal strength against what we know to be true in the course of nature, such objections can have no weight." (Essays on the Intell. Powers, p. 54.) To the same purpose it is observed by Dr. Campbell, that "analogical evidence is generally more successful in silencing objections than in evincing truth. Though it rarely refutes, it frequently repels refutation; like those weapons which, though they cannot kill the enemy, will ward his blows." (Phil. of Rhet. Vol. I. p. 145.)

This estimate of the force of analogical reasoning, considered as a weapon of controversy, is discriminating and judicious. The occasion on which the logician wields it to the best advantage is, undoubtedly, in repelling the objections of an adversary. But after the foregoing observations, I may be permitted to express my doubts, whether both of these ingenious writers have not somewhat underrated the importance of analogy as a medium of proof, and as a source of new information.-I acknowledge, at the same time, that between the positive and the negative applications of this species of evidence, there is an essential difference. When employed to refute an objection, it may often furnish an argument irresistibly and unanswerably convincing: when employed as a medium of proof, it can never authorize more than a probable conjecture, inviting and encouraging farther examination. In some instances, however, the probability resulting from a concurrence of different analogies may rise so high, as to 'produce an effect on the belief scarcely distinguishable from moral certainty,

the unity of truth ;-a most important fact in the theory of the human mind, and a fact which must strike every candid inquirer with increasing evidence, in proportion to the progress which he makes in the interpretation of Nature. Hence the effect of philosophical habits in animating the curiosity, and in guiding the inventive powers; and hence the growing confidence which they inspire in the ever consistent and harmonious conclusions of inductive science. It is chiefly (as Bacon has observed) from partial and desultory researches that scepticism arises; not only as such researches suggest doubts which a more enlarged acquaintance with the universe would dispel, but as they withdraw the attention from those comprehensive views which combine into a symmetrical fabric-all whose parts mutually lend to each other support and stability—the most remote, and seemingly the most unconnected discov eries. "Etenim symmetria scientia, singulis scilicet "partibus se invicem sustinentibus, est, et esse debet,

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vera atque expedita ratio refellendi objectiones minorum "gentium: Contra, si singula axiomata, tanquam baculos "fascis seorsim extrahas, facile erit ea infirmare, et pro "libito, aut flectere, aut frangere. Num non in aula spatiosa "consultius foret, unum accendere cereum, aut lychnu"chum suspendere, variis luminibus instructum, quo omnia "simul perlustrentur, quam in singulos angulos quaqua"versus exiguam circumferre lucernam ?"'*

De Augment. Scient. Lib. i.

II.

Use and Abuse of Hypotheses in Philosophical Inquiries.-Difference between Gratuitous Hypotheses, and those which are supported by presumptions suggested by Analogy.-Indirect Evidence which a Hypothesis may derive from its agreement with the Phenomena.-Cautions against extending some of these conclusions to the Philosophy of the Human Mind.

As some of the reasonings in the former part of this Section may, at first sight, appear more favourable to the use of Hypotheses than is consistent with the severe rules of the Inductive Logic, it may not be superfluous to guard against any such misapprehensions of my meaning, by subjoining a few miscellaneous remarks and illustrations.

The indiscriminate zeal against hypotheses, so generally avowed at present by the professed followers of Bacon, has been much encouraged by the strong and decided terms in which, on various occasions, they are reprobated by Newton.* But the language of this great man, when he happens to touch upon logical questions, must not always be too literally interpreted. It must be qualified and limited, so as to accord with the exemplifications which he himself has given of his general rules. Of the truth of this remark, the passages now alluded to afford a satisfac'tory proof; for, while they are expressed in the most unconditional and absolute terms, so many exceptions to them occur in his own writings, as to authorize the conclusion, that he expected his readers would of themselves be able to supply the obvious and necessary comments. is probable that, in these passages, he had more particularly in his eye the Vortices of Des Cartes.

It

#66 Hypotheses non fingo. Quicquid enim ex phenomenis non deducitur hypothesis vocanda est, et hypotheses, seu metaphysicæ, seu physicæ, seu qualitatum occultarum, seu mechanicæ, in philosophia experimentali locum non habent." See the general Scholium at the end of the Principia.

"The votaries of hypotheses (says Dr. Reid) have often "been challenged to shew one useful discovery in the "works of nature that was ever made in that way."* In reply to this challenge, it is sufficient, on the present occasion to mention the theory of Gravitation, and the Copernican system.† Of the former, we have the testimony of Dr. Pemberton, that it took its first rise from a conjecture or hypothesis suggested by analogy; nor indeed could it be considered in any other light, till that period in Newton's life, when, by a calculation founded on the accurate measurement of the earth by Picard, he evinced the coincidence between the law which regulates the fall of heavy bodies, and the power which retains the Moon in her orbit. The Copernican system, however, furnishes a case still stronger, and still more directly applicable to our purpose; inasmuch as the only evidence which the author was able to offer in its favour, was the advantage which it possessed over every other hypothesis, in explaining, with simplicity and beauty, all the phenomena of the heavens. In the mind of Copernicus, therefore, this system was nothing more than a hypothesis;--but it was a hypothesis conformable to the universal analogy of nature, always accomplishing her ends by the simplest means. "C'est pour la simplicité (says Bailly) que Co

pernic replaça le soleil au centre du monde; c'est pour "elle que Kepler va détruire tous les épicycles que Copernic avoit laissés subsister: peu de principes, de grands

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* Essays on the Intellectual Powers of Man, p. 88, 4to edit. In another part of the same volume, the following assertion occurs. "Of all the discoveries that have been made concerning the inward structure of the human body, never one was made by conjecture.- The same thing may be said, with justice, of every other part of the works of God, wherein any real discovery has been made. Such discoveries have always been made by patient observation, by accurate experiments, or by conclusions drawn by strict reasoning from observations and experiments; and such discoveries have always tended to refute, but not to confirm, the theories and hypotheses which ingenious men had invented." Ibid. p. 49.

† See note (R.)

moyens en petit nombre, des phénomènes infinis et variés, "voilà le tableau de l'univers."*

According to this view of the subject, the confidence which we repose in Analogy rests ultimately on the evidence of experience; and hence, an additional argument in favour of the former method of investigation, when cautiously followed; as well as an additional proof of the imperceptible shades by which Experience and Analogy run into each other.

Nor is the utility of hypothetical theories confined to those cases in which they have been confirmed by subsequent researches: it may be equally great, where they have completely disappointed the expectations of their authors. Nothing, I think, can be juster than Hartley's

*Histoire de l'Astronomie Moderne, Tome II. p. 2.

From this anticipation of simplicity in the laws of nature (a logical principle not less universally recognized among ancient than among modern philosophers,) Bailly has drawn an argument in support of his favourite hypothesis concerning the origin of the sciences. His words are these: "La simplicité n'est pas essentiellement un principe, un axiôme, c'est le résultat des travaux ; ce n'est pas une idee de l'enfance du monde, elle appartient à la maturité des hommes; c'est la plus grande des vérités que l'observation constante arrache à l'illusion des effets: ce ne peut être qu'un reste de la science primitive. Lorsque chez un peuple, possesseur d'une mythologie compliquée, et qui n'a d'autre physique que ces fables, les philosophes, voulant réduire la nature à un seul principe, annonceront que l'eau est la source de toutes choses, ou le feu l'agent universel, nous dirons à ces philosophes : vous parlez une langue que n'est pas la vôtre; vous avez saisi par un instinct philosophique ces vérités audessus de votre siècle, de votre nation, et de vous-mêmes ; c'est la sagesse des anciens qui vous a été transmise par tradition,"-&c. &c. &c.-Ibid. p. 4.

To the general remark which introduces this passage I readily subscribe. The confidence with which philosophers anticipate the simplicity of Nature's laws is unquestionably the result of experience, and of experience alone; and implies a far more extensive knowledge of her operations than can be expected from the uninformed multitude. The inference, however, deduced from this, by the ingenious and eloquent, but sometimes too fanciful historian, is ret a little precipitate. The passion for excessive simplification, so remarkably exemplified in the physical systems of the Greeks, seems to be sufficiently accounted for by their scanty stock of facts, combined with that ambition to explain every thing from the smallest possible number of data, which, in all ages of the world, has been one of the most common infirmities of genius. On the other hand, the principle in question, when stated in the form of a proposition, is of so abstract and metaphysical a nature, that it is highly improbable it should have survived the shock of revolutions which had proved fatal to the memory of particular discoveries. The arts, it has been frequently observed, are more easily transmitted by mere tradition, from one generation to another, than the speculative sciences; and, for a similar reason, physical systems are far less likely to sink into oblivion, than abstract maxims, which have no immediate reference to objects of sense, or to the ordinary concerns of life.