and imagination; and, at last, of pure intellection. When they are objects of memory and of imagination, they get the name of phantasms. When, by farther refinement, and being stripped of their peculiarities, they become objects of science, they are called intelligible species; so that every immediate object, whether of sense, of memory, of imagination, or of reasoning, must be some phantasm, or species, in the mind itself.

The followers of Aristotle, especially the schoolmen, made great additions to this theory; which the author himself mentions very briefly, and with an appearance of reserve. They entered into large disquisitions with regard to the sensible species, what kind of things they are; how they are sent forth by the object, and enter by the organs of the senses; how they are preserved, and refined by various agents, called internal senses, concerning the number and offices of which they had many controversies. (Essays on the Intellectual Powers of Man, p. 25.)

The Platonists, too, although they denied the great doctrine of the Peripatetics, that all the objects of human understanding enter at first by the senses; and maintained, that there exist eternal and immutable ideas, which were prior to the objects of sense, and about which all science was employed; yet appear to have agreed with them in their notions concerning the mode in which external objects are perceived. This, Dr. Reid infers, partly from the silence of Aristotle about any difference between himself and his master upon this point; and partly from a passage in the seventh book of Plato's Republic; in which he compares the process of the mind in perception, to that of a person in a cave, who sees not external objects themselves, but only their shadows. (Essay, p. 99.)

"Two thousand years after Plato," (continues Dr. Reid,) "Mr. Locke, who studied the operations of the human mind so much, and with so great success, represents our manner of perceiving external objects, by a similitude very much resembling that of the cave. Methinks,' says he, the understanding is not much unlike a closet, wholly shut from light, with only some little opening left, to let in external visible resemblances or ideas of things without. Would the pictures coming into such a dark room but stay there, and lie so orderly as to be found upon occasion, it would very much resemble the understanding of a man, in reference to all objects of sight, and the ideas of them.' (Locke on Human Understanding, book ii. chap. ii. § 17.)

"Plato's subterranean cave, and Mr. Locke's dark closet, may be applied with ease to all the systems of perceptions that have been invented for they all suppose, that we perceive not external objects immediately and that the immediate objects of perception, are only certain shadows of the external objects. Those shadows, or images, which we immediately perceive, were by the ancients called species, forms, phantasms. Since the time of Des Cartes,

they have commonly been called ideas;* and by Mr. Hume, im

* DOCTOR REID remarks, that Des Cartes rejected a part only of the ancient theory of perception, and adopted the other part. "That theory," says he, "may be divided into two parts: the first, that images, species, or forms of external objects, come from the object, and enter by the avenues of the senses to the mind: the second part is, that the external object itself is not perceived, but only the species or image of it in the mind. The first part, Des Cartes and his followers rejected and refuted by solid arguments; but the second part, neither he nor his followers have thought of calling in question; being persuaded that it is only a representative image in the mind of the external object that we perceive, and not the object itself. And this image, which the peripatetics called a species, he calls an idea, changing the name only, while he admits the thing."

The account which this passage contains of Des Cartes' doctrine concerning perception, is, I believe, agreeable to his prevailing opinion, as it may be collected from the general tenor of his writings; and the observation with which it concludes is undoubtedly true, that neither he nor any of his followers ever called in question the existence of ideas, as the immediate objects of our perception. With respect, however, to the first part of the ancient theory, as here stated, it may be proper to remark, that Des Cartes, although evidently by no means satisfied with it, sometimes expresses himself as if he had rather doubted of it, than expressly denied it; and at other times, when pressed with objections to his own particular system, he admits, at least in part, the truth of it. The following passage is one of the most explicit I recollect, in opposition to the ancient doctrine.

"Observandum præterea animam nullis imaginibus ab objectis ad cerebrum missis egere ut sentiat, (contra quam communiter philosophi nostri statuunt,) aut ad minimum longe aliter illarum imaginum naturam concipiendam esse quam. vulgo fit. Quum enim circa eas nil considerent, præter similitudinem earum cum objectis quæ repræsentant, non possunt explicare, qua ratione ab objectis formari queant, et recipi ab organis sensuum exteriorum, et demum nervis ad cerebrum transvehi. Nec alia causa imagines istas fingere eos impulit, nisi quod viderent mentem nostram efficaciter pictura excitari ad apprehendendum objectum illud, quod exhibit: ex hoc enim judicarunt, illam eodem modo excitandam, ad apprehendenda ea quæ sensus movent, per exiguas quasdam imagines, in capite nostro delineatas. Sed nobis contra est advertendum, multa præter imagines esse, quæ cogitationes excitant, ut exempli gratia, verba et signa, nullo modo similia iis quæ significant."-Dioptric. cap. 4, sec. 6.

In his third meditation, which contains his celebrated argument for the existence of a Deity, the following passage occurs.

"Sed hic præcipue de iis est quærendum quas tanquam a rebus extra me existentibus desumptas considero, quænam me moveat ratio ut illas istis rebus similes esse existime; nempe ita videor doctus a natura, et præterea experior illas non a mea voluntate nec proinde a me ipso pendere, sæpe enim vel invito obversantur, ut jam, sive velim sive nolim, sentio calorem, et ideo puto sensum illum, sive ideam caloris a re a me diversa, nempe ab ignis, cui assideo calore mihi advenire, nihilque magis obvium est, quam ut judicem istam rem suam similitudinem potius, quam aliud quid in me immittere: quæ rationes an satis firmæ sint, jam videbo. Cum hic dico me ita doctum esse a natura, intelligo tantum spontaneo quodam impetu me ferri ad hoc credendum, non lumine aliquo naturali mihi ostendi esse verum, quæ duo multum discrepant, nam quæcumque lumine naturali mihi ostenduntur, (ut quod ex eo quod dubitem sequatur me esse, et similia,) nullo modo dubia esse possunt quia nulla alia facultas esse potest, cui æque fidam ac lumini isti, quæque illa non vera possit docere; sed quantum ad impetus naturales, jam sæpe olim judicavi me ab illis in deteriorem partem fuisse impulsum cum de bono eligendo ageretur, nec video cur iisdem in ulla alia re magis fidam. Deinde quamvis ideæ illæ a voluntate mea non pendeant, non ideo constat ipsas a rebus extra me positis necessario procedere ; ut enim impetus illi, de quibus mox loquebar, quamvis in me sint, a voluntate tamen mea diversi esse videntur, ita forte etiam aliqua alia est in me facultas nondum mihi satis cognita istarum idearum efïectrix, ut hactenus semper visum est illas, dum somnio, absque ulla rerum externarum ope in me formari; ac denique quamvis a rebus a me diversis procederent, non inde sequitur illas rebus istis similes esse debere; quinimo in multis sæpe magnum

pressions. But all philosophers, from Plato to Mr. Hume, agree in this, that we do not perceive external objects immediately; and that the immediate object of perception must be some image present to the mind." On the whole, Dr. Reid remarks, "that in their sentiments concerning perception, there appears an uniformity which rarely occurs upon subjects of so abstruse a nature." (Reid, p. 116, 117.)

The very short and imperfect view we have now taken of the common theories of perception, is almost sufficient, without any commentary, to establish the truth of the two general observations formerly made; for they all evidently proceed on a supposition, suggested by the phenomena of physics, that there must of necessity exist some medium of communication between the objects of perception and the percipient mind; and they all indicate a secret conviction in their authors, of the essential distinction between mind and matter; which, although not rendered, by reflection, sufficiently precise and satisfactory, to show them the absurdity of attempting to explain the mode of their communication; had yet such a degree of influence on their speculations, as to induce them to exhibit their supposed medium under as mysterious and ambigu ous a form as possible, in order that it might remain doubtful, to which of the two predicaments, of body or mind, they meant that it should be referred. By refining away the grosser qualities of matter; and by allusions to some of the most aërial and magical appearances it assumes, they endeavored, as it were, to spiritualize the nature of their medium; while at the same time, all their language concerning it, implied such a reference to matter, as was necessary for furnishing a plausible foundation, for applying to it the received maxims of natural philosophy.

Another observation, too, which was formerly hinted at, is confirmed by the same historical review; that, in the order of inquiry, the phenomena of vision had first engaged the attention of philosophers, and had suggested to them the greater part of their language, with respect to perception in general; and that, in consediscrimen videor deprehendisse; sic, exempli causa, duas diversas solis ideas apud me invenio, unam tanquain a sensibus haustam, et quæ maxime inter illas quas adventitias existimo est recensenda, per quam mihi valde parvus apparet; aliam vero ex rationibus astronomiæ desumptam, hoc est ex notionibus quibusdam mihi innatis elicitam vel quocumque alio modo a me factum, per quam aliquoties major quam terra exhibetur; utraque profecto similis eidem soli extra me existenti esse non potest, et ratio persuadet illam ei maxime esse dissimilem, quæ quam proxime ab ipso videtur emanasse. Quæ omnia satis demonstrant me non hactenus ex certo judicio, sed tantum ex cæco aliquo impulsu credidisse res quasdam a me diversis existere, quæ ideas sive imagines suas per organa sensuum, vel quolibet alio pacto mihi immittant.

Among other animadversions upon this meditation sent to Des Cartes by one of his correspondents, it is objected:"Videris vertere in dubium non tantum utrum idea aliquæ procedant ex rebus externis, sed etiam utrum omnino sint externæ res alique." To which Des Cartes answers: "Notandum est, me non affirmasse ideas rerum materialium ex mente deduci, ut non satis bona fide hic fingis; expresse enim postea ostendi ipsas a corporibus sæpe advenire, ac per hoc corporum existentiam probari."-Vide Objectiones in Meditationes Renati Des Cartes, cum ejusdem ad illas Responsionibus.

quence of this circumstance, the common modes of expression on the subject unphilosophical and fanciful at best, even when applied to the sense of seeing, are, in the case of all the other senses, obviously unintelligible and self-contradictory. As to objects of sight, says Dr. Reid, I understand what is meant by an image of their figure in the brain: but how shall we conceive an image of their color, where there is absolute darkness? And, as to all other objects of sense, except figure and color, I am unable to conceive what is meant by an image of them. Let any man say, what he means by an image of heat and cold, an image of hardness or softness, an image of sound or smell, or taste. The word image, when applied to these objects of sense, has absolutely no meaning. This palpable imperfection in the ideal theory, has plainly taken rise from the natural order in which the phenomena of perception present themselves to the curiosity.

The mistakes, which have been so long current in the world, about this part of the human constitution, will, I hope, justify me for prosecuting the subject a little farther; in particular, for illus trating at some length, the first of the two general remarks already referred to. This speculation I enter upon the more willingly, that it affords me an opportunity of stating some important principles with respect to the object, and the limits, of philosophical inquiry; to which I shall frequently have occasion to refer, in the course of the following disquisitions.

SECTION II.

Of certain natural Prejudices, which seem to have given rise to the common Theories of Perception.

It seems now to be pretty generally agreed among philosophers, that there is no instance in which we are able to perceive a necessary connexion between two successive events; or to comprehend in what manner the one proceeds from the other, as its cause. From experience indeed we learn that there are many events, which are constantly conjoined, so that the one invariably follows the other: but it is possible, for anything we know to the contrary, that this connexion, though a constant one, as far as our observation has reached, may not be a necessary connexion; nay, it is possible, that there may be no necessary connexions among any of the phenomena we see and, if there are any such connexions existing, we may rest assured that we shall never be able to discover them.*

* In consequence of the inferences which Mr. Hume has deduced from this doctrine concerning cause and effect, some later authors have been led to dispute its truth; not perceiving that the fallacy of this part of Mr. Hume's system does not consist in his premises, but in the conclusion which he draws from them.

That the object of the physical inquirer is not to trace necessary connexions, or to ascertain the efficient causes of phenomena, is a principle which has been frequently ascribed to Mr. Hume as its author, both by his followers and by his op

I shall endeavor to show, in another part of this work, that the doctrine I have now stated does not lead to these skeptical conclusions, concerning the existence of a First Cause, which an author ponents; but it is, in fact, of a much earlier date, and has been maintained by many of the most enlightened, and the least skeptical of our modern philosophers: nor do I know that it was ever suspected to have a dangerous tendency, till the publication of Mr. Hume's writings. "If we except," says Dr. Barrow, "the mutual causality and dependence of the terms of a mathematical demonstration, I do not think that there is any other causality in the nature of things, wherein a necessary consequence can be founded. Logicians do indeed boast of I do not know what kind of demonstrations from external causes either efficient or final, but without being able to show one genuine example of any such; nay, I imagine it is impossible for them so to do. For there can be no such connexion of an external efficient cause with its effect, (at least none such can be understood by us,) through which, strictly speaking, the effect is necessarily supposed by the supposition of the efficient cause, or any determinate cause by the supposition of the effect." He adds afterwards, "Therefore there can be no argumentation from an efficient cause to the effect, or from an effect to the cause which is lawfully necessary."-Mathematical Lectures read at Cambridge.

Dr. Butler too, in his discourse on the ignorance of man, has remarked, that "it is in general no more than effects, that the most knowing are acquainted with ; for as to causes, they are entirely in the dark as the most ignorant. What are the laws," he continues, "by which matter acts on matter, but certain effects, which some having observed to be frequently repeated, have reduced to general rules?"-Butler's Sermons.

"The laws of attraction and repulsion," says Dr. Berkely, "are to be regarded as laws of motion, and these only as rules or methods observed in the productions of natural effects, the efficient and final causes whereof are not of mechanical consideration. Certainly, if the explaining a phenomenon be to assign its proper efficient and final cause, it should seem the mechanical philosophers never explained anything; their province being only to discover the laws of nature; that is, the general rules and method of motion; and to account for particular phenomena, by reducing them under, or showing their conformity to such general rules." -Siris; or Philosophical Inquiries concerning the Virtues of Tar-Water, p. 108. "The words attraction and repulsion may, in compliance with custom, be used where, accurately speaking, motion alone is meant."-Ibid. p. 114.

"Attraction cannot produce, and in that sense account, for the phenomena; being itself one of the phenomena produced and to be accounted for."-Ibid. p. 115. "There is a certain analogy, constancy, and uniformity in the phenomena or appearances of nature, which are a foundation for general rules: and these are a grammar for the understanding of nature, or that series of effects in the visible world, whereby we are enabled to foresee what will come to pass in the natural course of things. Plotinus observes, in his third Ennead, that the art of presaging, is in some sort the reading of natural letters denoting order, and that so far forth as analogy obtains in the universe, there may be vaticination. And in reality, he that foretells the motions of the planets, or the effects of medicines, or the result of chemical or mechanical experiments, may be said to do it by natural vaticination."—Ibid. p. 120, 121.

"Instruments, occasions, and signs, occur in, or rather make up, the whole visible course of nature."-Ibid. p. 123.

The following very remarkable passage from Mr. Locke shows clearly that this eminent philosopher considered the connexion between impulse and motion, as a conjunction which we learn from experience only; and not as a consequence deducible from the consideration of impulse, by any reasoning à priori. The passage is the more curious, that it is this particular application of Mr. Hume's doctrine, that has been generally supposed to furnish the strongest objection against it.

Another idea we have of body, is the power of communicating motion by impulse; and of our souls, the power of exciting motion by thought. These ideas, the one of body, the other of our minds, every day's experience clearly furnishes us with; but if here again we inquire how this is done, we are equally in the dark. For in the communication of motion by impulse, wherein as much motion