city, to the general economy of the Universe. "When Copernicus (says Mr. Maclaurin) considered the form, disposition, and motions of the system, as they were then represented after Ptolemy, he found the whole void of order, symmetry, and proposition; like a piece (as he expresses himself) made up of parts copied from different originals, which, not fitting each other, should rather represent a monster than a man. He therefore perused the writings of the ancient philosophers, to see whether any more rational account had ever been proposed of the motions of the Heavens. The first hint he had was from Cicero, who tells us, in his Academical Questions, that Nicetas, a Syracusian, had taught that the earth turns round on its axis, which made the whole heavens appear to a spectator on the earth to turn round it daily. Afterwards, from Plutarch he found that Philolaus the Pythagorean had taught that the earth moved annually round the sun. He immediately perceived, that, by allowing these two motions, all the perplexity, disorder, and confusion he had complained of in the celestial motions vanished; and that, instead of these, a simple regular disposition of the orbits, and a harmony of the motions appeared, worthy of the great author of the world.*

Of the truth of this hypothesis, the discoveries of the last century have afforded many new proofs of a direct and even demonstrative nature; and yet, it may be fairly

* Account of Newton's Philosophical Discoveries, p. 45. (2d Edit.) This presumptive argument, as it presented itself to the mind of Copernicus, is thus stated by Bailly. "Les hommes sentent que la nature est simple; les stations et les rétrogradations des planetes offroient des apparences bizarres; le principe, qui les ramenoit à une marche simple, et naturelle, ne pouvoit étre qu'unc vérité.” Hist. de l'Astron. Mod. Tom. I. p. 351.

questioned, whether to Copernicus and Galileo, the analogical reasoning stated in the preceding quotation, did not, of itself, appear so conclusive, as to supersede the necessity of any farther evidence. The ecclesiastical persecutions which the latter encountered in defence of his supposed heresy, sufficiently evinces the faith which he reposed in his astronomical creed.

It is, however, extremely worthy of remark, with respect to the Copernican system, that it affords no illustration whatever of the justness of Hartley's logical maxim. The Ptolemaic system was not demonstrably inconsistent with any phenomena known in the sixteenth century: and, consequently, the presumption for the new hypothesis did not arise from its exclusive coincidence with the facts, but from the simplicity and beauty which it possessed as a theory. The inference to be deduced from it is, therefore, not in favour of hypotheses in general, but of hypotheses sanctioned by analogy.

The fortunate hypothesis of a Ring encircling the body of Saturn, by which Huyghens accounted, in a manner equally simple and satisfactory, for a set of appearances which, for forty years, had puzzled all the astronomers or Europe, bears, in all its circumstances, a closer resemblance than any other instance I know of, to the key of a cipher. Of its truth it is impossible for the most sceptical mind to entertain any doubt, when it is considered, that it not only enabled Huyghens to explain all the known phenomena, but to predict those which were afterwards to be observed. This instance, accordingly, has had much stress laid upon it by different writers, particu

larly by Gravesande and Le Sage."* I must own, I am somewhat doubtful, if the discovery of a key to so limited and insulated a class of optical facts, authorizes any valid argument for the employment of mere hypotheses, to decipher the complicated phenomena resulting from the general laws of nature. It is, indeed, an example most ingeniously and happily selected: but would not perhaps have been so often resorted to, if it had been easy to find others of a similar description.

2. The chief objection, however, to Hartley's comparison of the theorist to the decipherer is, that there are few, if any, physical hypotheses, which afford the only way of explaining the phenomena to which they are applied; and therefore, admitting them to be perfectly consistent with all the known facts, they leave us in the same state of uncertainty, in which the decipherer would find himself, if he should discover a variety of keys to the same cipher. Des Cartes acknowledges, that the same effect might, upon the principles of his philosophy, admit of manifold explanations; and that nothing perplexed him more than to know which he ought to adopt, in preference to the others. "The powers of nature, (says he) I must confess, are so ample, that no sooner do I observe any particular effect, than I immediately perceive that it may be deduced from my principles, in a variety of different ways; and nothing, in general, appears to me more diffi

* Gravesande, Introd. ad. Philosoph. §§ 979 945.

Opuscules de le Sage, published by M. Prévost. Premier Mémoire, § 25. The latter writer mentions the theory in question, as a hypothesis which received no countenance whatever from the analogy of any preceding astronomical discovery.

cult, than to ascertain by which of these processes it is really produced."* The same remark may, (with a very few exceptions) be extended to every hypothetical theory which is unsupported by any collateral probabilities arising from experience or analogy; and it sufficiently shows, how infinitely inferior such theories are, in point of evidence, to the conclusions obtained by the art of the deci pherer. The principles, indeed, on which this last art proceeds, may be safely pronounced to be nearly infallible.

In these strictures upon Hartley, I have endeavoured to do as much justice as possible to his general argument, by keeping entirely out of sight the particular purpose which it was intended to serve. By confining too much his attention to this, Dr. Reid has been led to carry, farther than was necessary or reasonable, an indiscriminate zeal against every speculation to which the epithet hypothetical can in any degree be applied. He has been also led to overlook the essential distinction between hypothetical inferences from one department of the Material World to another, and hypothetical inferences from the Material World to the Intellectual. It was with the view of apologizing for inferences of the latter description, that Hartley advanced the logical principle which gave occasion to the foregoing discussion; and therefore, I apprehend, the proper answer

Dissertatio de Methodo. In the sentence immediately following, Des Cartes mentions the general rule which he followed, when such an embarrassment occurred. "Hinc aliter me extricare non possum, quàm si rursus aliqua experimenta quæram; quæ talia sint, ut eorum idem non sit futurus eventus, si hoc modo quam si illo explicetur." The rule is excellent; and it is only to be regretted, that so few exemplifications of it are to be found in his writings.

3 D

to his argument is this:-Granting your principle to be true in all its extent, it furnishes no apology whatever for the Theory of Vibrations. If the science of mind admit of any illustration from the aid of hypotheses, it must be from such hypotheses alone as are consonant to the analogy of its own laws. To assume, as a fact, the existence of analogies between these laws and those of matter, is to sanction that very prejudice which it is the great object of the inductive science of mind to eradicate.

I have repeatedly had occasion, in some of my former publications, to observe, that the names of almost all our mental powers and operations are borrowed from sensible images. Of this number are intuition; the discursive faculty; attention; reflection; conception; imagination ; apprehension; comprehension; abstraction; invention; capacity; penetration; acuteness. The case is precisely similar with the following terms and phrases, relative to a different class of mental phenomena;—inclination; aversion; deliberation; pondering; weighing the motives of our actions; yielding to that motive which is the strongest; -expressions (it may be remarked in passing,) which, when employed, without a very careful analysis of their import, in the discussion concerning the liberty of the will, gratuitously prejudge the very point in dispute; and give the semblance of demonstration, to what is, in fact, only a series of identical propositions, or a sophistical circle of words.*

"Nothing (says Berkeley) seems more to have contributed towards engaging men in controversies and mistakes with regard to the nature and operations of the mind, than the being used to speak of those things in terms borrowed from sensible ideas. For example, the will is termed the