Secondly, by misleading us in those anticipations of the future from the past, which our constitution disposes us to form, and which are the great foundation of our conduct in life.

to our thoughts, or suggested to us from without, revives a long train of particulars associated in the mind with each other; to which train, not being able to account otherwise for the concatenation of its parts, we give the name of a dream. After all I am very far from supposing that I have exhausted this subject; and I shall be fully satisfied with the success of my inquiries, if those who are qualified to distinguish between legitimate and hypothetical theories shall admit, that I have pointed out the plan on which these phenomena should be studied, and have made some progress, how small soever, towards its execution. Much additional light, I am sensible, might have been easily thrown on this part of our constitution, as well as upon many others, if I had not imposed on myself the restraint of adhering wherever it was at all possible, to the modes of speaking employed by my predecessors in describing our mental operations.

One remark I must beg leave to recommend to the consideration of those who may hereafter engage in this research; that, among the astonishing appearances exhibited by the mind in sleep, a very large proportion are precisely analogous to those of which we are every moment conscious while awake. If the exciting causes, for example, of our dreams seem mysterious and inscrutable, is not the fact the same with the origin of every idea or thought, which spontaneously solicits our notice? The only difference is, that in the latter instance, in consequence of long and constant familiarity, they are surveyed by all with little wonder, and by most with hardly any attention. In the former instance, they rouse the curiosity of the most illiterate, from their comparative infrequency, and from the contrast which, in some respects, they present to the results of our habitual experience. It is thus, that a peasant who has been accustomed from his infancy to see, without any emotion, the fall of heavy bodies to the ground, never fails to express the liveliest admiration when he first witnesses the powers of the loadstone.

In such cases, the researches of genuine science have a tendency to produce two moral effects equally beneficial. The one is to illustrate the unity of design in nature, by reconciling what seems, from its rarity or singularity, to be mysterious or incomprehensible, with the general laws which are familiarized to us by daily experience; the other to counteract the effects of familiarity in blunting our natural curiosity with respect to these laws, by leading the thoughts to some of their more curious and apparently anomalous applications.

The phenomena of dreaming may perhaps, in this last point of view, form an article not altogether useless in the natural history of man; inasmuch as they contribute to attract our attention to those intellectual powers, from which it is so apt to be withdrawn by that external world, which affords the first, and (for the common purposes of life) the most interesting field for their exercise. In my own case, at least, this supposition has been exactly verified; as the speculations concerning the human mind which I have ventured to present to the public, all took their rise from the subject to which this note refers. The observations which I have stated with respect to it in the text (excepting a very few paragraphs since added) were written at the age of eighteen, and formed a part of the first philosophical essay which I recollect to have attempted. The same essay contained the substance of what I have introduced in chapter third, concerning the belief accompanying conception; and of the remarks stated in the third section of chapter fifth, on the extent of the power which the mind has over the train of its thoughts. When I was afterwards led professionally, at the distance of many years, to resume the same studies, this short manuscript was almost the only memorial I had preserved of these favorite pursuits of my early youth; and from the views which it recalled to me, insensibly arose the analysis I have since undertaken of our intellectual faculties in general.

For some indulgence to the egotism of this note, I must trust to the good nature of my readers. It has been lengthened much beyond my original intention, by an anxiety (not, I hope, unpardonable in an author) to fix the date of some of my disquisitions and conclusions, of which it is highly probable I may magnify the importance beyond their just value. The situation of a public teacher, I must beg leave to add, by giving an immediate circulation to the doctrines he delivers, exposes him to many inconveniences which other classes of literary men have in their power to avoid.

Thirdly, by connecting in the mind erroneous opinions with truths which irresistibly command our assent, and which we feel to be of importance to human happiness.

A short illustration of these remarks will throw light on the origin of various prejudices; and may, perhaps, suggest some practical hints with respect to the conduct of the understanding.

I. I formerly had occasion to mention several instances of very intimate associations formed between two ideas which have no necessary connexion with each other. One of the most remarkable is, that which exists in every person's mind between the notions of color and of extension. The former of these words expresses (at least in the sense in which we commonly employ it) a sensation in the mind; the latter denotes a quality of an external object; so that there is, in fact, no more connexion between the two notions than between those of pain and of solidity;* and yet, in conse

Before concluding these remarks, I cannot help reminding my readers once more that my fundamental principle with respect to the state of the mind in sleep is,-not, that the power of volition is then suspended; but that the influence of the will over the faculties both of mind and body is then interrupted. See pp. 200 -202. I mention this chiefly, in order to mark the difference between my doctrine and that maintained in Dr. Darwin's Zoonomia. According to this ingenious writer, "the power of volition is totally suspended in perfect sleep."-Zoonomia, vol. i. p. 315" In the incubus," he observes, "the desire of moving the body is painfully exerted; but the power of moving it, or volition, is incapable of action till we awake," p. 288. Would he not have stated the fact more correctly, if he had said, that volition is painfully exerted; but that the power of moving the body is suspended? In the very accurate phraseology of Mr. Locke, "volition is an act of the mind, knowingly exerting that dominion it takes itself to have over any part of the man, by employing it in, or withholding it from, any particular action." This act of the mind Dr. Darwin expresses by the word desire; an indistinctness still extremely common among metaphysical writers; although it was long ago remarked and censured by the eminent author just quoted: "I find," says Locke, "the will often confounded with desire, and one put for the other; and that by men who would not willingly be thought not to have very distinct notions of things, and not to have written very clearly about them."-Essay on Human Understanding, vol i. p. 203, 13th edit.

* Dr. Reid has, with great truth, observed, that Des Cartes' reasonings against the existence of the secondary qualities of matter, owe all their plausibility to the ambiguity of words. When he affirms, for example, that the smell of a rose is not in the flower but in the mind, his proposition amounts only to this, that the rose is not conscious of the sensation of smell; but it does not follow from Des Cartes' reasonings, that there is no quality in the rose which excites the sensation of smell in the mind;-which is all that any person means when he speaks of the smell of that flower. For the word smell, like the names of all secondary qualities, signi.fies two things, a sensation in the mind, and the unknown quality which fits it to excite that sensation.* The same remark applies to that process of reasoning by which Des Cartes attempts to prove that there is no heat in the fire.

All this, I think, will be readily allowed with respect to smells and tastes, and also with respect to heat and cold; concerning which I agree with Dr. Reid, in thinking that Des Cartes' doctrine, when cleared of that air of mystery which it derives from the ambiguity of words, differs very little, if at all, from the commonly

*Some judicious remarks on this ambiguity in the names of secondary qualities, are made by Malebranche.

"It is only," says he, "since the time of Des Cartes, that those confused and indeterminate questions, whether fire is hot, grass green, and sugar sweet, philosophers are in use to answer, by distinguishing the equivocal meaning of the words expressing sensible qualities. If by heat, cold, and savor, you understand such and such a disposition of parts, or some unknown motion of insensible particles, then fire is hot, grass green, and sugar sweet. But if by heat and other qualities you understand what I feel by fire, what I see in grass, &c., fire is not hot, nor grass green, for the heat I feel, and the colors I see, are only in the soul."

quence of our always perceiving extension, at the same time at which the sensation of color is excited in the mind, we find it im

received notions. But the case seems to be different with respect to colors, of the nature of which the vulgar are apt to form a very confused conception, which the philosophy of Des Cartes has a tendency to correct. Dr. Reid has justly distinguished the quality of color from what he calls the appearance of color, which last can only exist in a mind. Now I am disposed to believe, that when the vulgar speak of color, they commonly mean the appearance of color; or rather they associate the appearance and its cause so intimately together, that they find it impossible to think of them separately. The sensation of color never forms one simple object of attention to the mind like those of smell and taste; but every time we are conscious of it, we perceive at the same time extension and figure. Hence it is, that we find it impossible to conceive color without extension, though certainly there is no more necessary connexion between them, than between extension and smell.

From this habit of associating the two together, we are led also to assign them the same place, and to conceive the different colors, or, to use Dr. Reid's language, the appearance of the different colors, as something spread over the surfaces of bodies. I own that when we reflect on the subject with attention, we find this conception to be indistinct, and see clearly that the appearance of color can exist only in a mind: but still it is some confused notion of this sort, which every man is disposed to form who has not been very familiarly conversant with philosophical inquiries. -1 find, at least, that such is the notion which most readily presents itself to my own mind.

Nor is this reference of the sensation, or appearance of color to an external object, a fact altogether singular in our constitution It is extremely analogous to the reference which we always make, of the sensations of touch to those parts of the body where the exciting causes of the sensations exist. If I strike my hand against a hard object, I naturally say, that I feel pain in my hand. The philosophical truth is, that I perceive the cause of the pain to be applied to that part of my body. The sensation itself I cannot refer in point of place to the hand, without conceiving the soul to be spread over the body by diffusion.

A still more striking analogy to the fact under our consideration, occurs in those sensations of touch which we refer to a place beyond the limits of the body; as in the case of pain felt in an amputated limb.

The very intimate combination to which the foregoing observations on the sensations of color relate, is taken notice of by d'Alembert in the Encyclopédie, as one of the most curious phenomena of the human mind.

"Il est très evident que le mot couleur ne désigne aucune propriété du corps, mais seulement une modification de notre âme; que la blancheur, par exemple, la rougeur, etc. n'existent que dans nous, et nullement dans le corps auxquels nous les rapportons; néanmoins par une habitude prise dès notre enfance, c'est une chose très singulière et digne de l'attention des métaphysiciens, que ce penchant que nous avons à rapporter à une substance matérielle et divisible, ce qui appar

* Dr. Akenside, in one of his notes on his Pleasures of Imagination, observes, that colors, as apprehended by the mind, do not exist in the body. By this qualification, he plainly means to distinguish what Dr. Reid calls the appearance of color, from color considered as a quality of matter. These two positions of Dr. Reid's do not appear to me quite consistent with each other. "If, in the perception of color, the sensation and the quality be so closely united as to be mistaken for one simple object of thought," does it not obviously follow, that it is to this compounded notion the name of color must in general be given? On the other hand, when it is said, that "the name of color is never given to the sensation but to the quality only," does not this imply, that every time the word is pronounced the quality is separated from the sensation, even in the imaginations of the vulgar?

† Dr. Reid is of opinion, that the vulgar always mean to express by the word color, a quality, and not a sensation. "Color," says he, "differs from other secondary qualities, in this, that whereas the name of the quality is sometimes given to the sensation which indicates it, and is occasioned by it, we never, as far as I can judge, give the name of color to the sensation, but to the quality only." This question is of no consequence for us to discuss at present, as Dr. Reid acknowledges in the following passage, that the sensation and quality are so intimately united together in the mind, that they seem to form only one simple object of thought. "When we think or speak of any particular color, however simple the notion may seen to be which is presented to the imagination, it is really in some sort compounded; it involves an unknown cause and a known effect. The name of color belongs indeed to the cause only, and not to the effect. But as the cause is unknown, we can form no distinct conception of it, but by its relation to the known effect. And therefore both go together in the imagination, and are so closely united that they are mistaken for one simple object of thought."-Inquiry into the Human Mind, chap.

vi. sect. 4.

possible to think of that sensation, without conceiving extension along with it.

Another intimate association is formed in every mind between the ideas of space and of time. When we think of an interval of duration, we always conceive it as something analogous to a line, and we apply the same language to both subjects. We speak of a long and short time, as well as of a long and short distance; and we are not conscious of any metaphor in doing so. Nay, so very perfect does the analogy appear to us, that Boscovich mentions it as a curious circumstance, that extension should have three dimensions, and duration only one.

This apprehended analogy seems to be founded wholly on an association between the ideas of space and of time, arising from our always measuring the one of these quantities by the other. We measure time by motion, and motion by extension. In an hour, the hand of the clock moves over a certain space; in two hours over double the space; and so on. Hence the ideas of space and of time become very intimately united, and we apply to the latter the words long and short, before and after, in the same manner as to the former.

The apprehended analogy between the relation which the different notes in the scale of music bear to each other, and the relation of superiority and inferiority, in respect of position, among material objects, arises also from an accidental association of ideas.

What this association is founded upon, I shall not take upon me to determine; but that it is the effect of accident, appears clearly from this, that it has not only been confined to particular ages and nations; but is the very reverse of an association which was

tient réellement à une substance spirituelle et simple; et rien n'est peut-être plus extraordinarie dans les opérations de notre âme, que de la voir transporter hors d'ellemême et étendre, pour ainsi dire, ses sensations sur une substance à laquelle elles ne peuvent appartenir.'

From the following passage in Condillac's Traité des Sensations, it appears that the phenomenon here remarked by d'Alembert, was, in Condillac's opinion, the natural and obvious effect of an early and habitual association of ideas. I quote it with the greater pleasure, that it contains the happiest illustration I have seen of the doctrine which I have been attempting to explain. The very same illustration is to be found in Reid's Inquiry, Chap. vi. Sect. 8. Condillac, however, has an unquestionable claim to it, in point of priority, although I have not the smallest doubt that it occurred to Reid in the course of his own speculations. Indeed, I have good ground for thinking he was not at all acquainted with Condillac's writings.

"On pourroit faire une supposition, où l'odorat apprendroit à juger parfaitement des grandeurs, des figures, des situations, et des distances. Il suffiroit d'un côté de soumettre les corpuscules odoriferans aux loix de la dioptrique, et de l'autre, de construire l'organe de l'odorat à peu près sur le modèle de celui de lavue; ensorte que les rayons odoriferans, après s'être croises à l'ouverture, frappassent sur une membrane intérieure autant de points distincts qu'il y en a sur les surfaces d'où ils seroient réflechis.

"En pareil cas, nous contracterions bientôt l'habitude d'étendre les odeurs sur les objets, et les philosophes ne manqueroient pas de dire, que l'odorat n'a pas besoin des leçons du toucher pour appercevoir des grandeurs et des figures."Œuvres de Condillac, edit. Amst. vol. v. p. 223.

once equally prevalent. It is observed by Dr. Gregory, in the preface to his edition of Euclid's works, that the more ancient of the Greek writers looked upon grave sounds as high, and acute ones as low; and that the present mode of expression on that subject was an innovation introduced at a later period.*

In the instances which have now been mentioned, our habits of combining the notions of two things become so strong, that we find it impossible to think of the one, without thinking at the same time of the other. Various other examples of the same species of combination, although, perhaps, not altogether so striking in degree, might easily be collected from the subjects about which our metaphysical speculations are employed. The sensations, for instance, which are excited in the mind by external objects, and the percep tions of material qualities which follow these sensations, are to be distinguished from each other only by long habits of patient reflection. A clear conception of this distinction may be regarded as the key to all Dr. Reid's reasonings concerning the process of nature in perception; and till it has once been rendered familiar to the reader, a great part of his writings must appear unsatisfactory and obscure. In truth, our progress in the philosophy of the human mind depends much more on that severe and discriminating judgment, which enables us to separate ideas which nature or habit have immediately combined, than on acuteness of reasoning or fertility of invention. And hence it is, that metaphysical studies are the best of all preparations for those philosophical pursuits which relate to the conduct of life. In none of these do we meet with casual combinations so intimate and indissoluble as those which occur in metaphysics; and he who has been accustomed to such discriminations as this science requires, will not easily be imposed on by that confusion of ideas, which warps the judgments of the multitude in moral, religious, and political inquiries.

* "Verum quidem est, quod hodierni musici sic loqui soleant, (acutum in alto reputantes et grave in imo,) quodque ex Græcis recentioribus nonnuli sic aliquando (sed raro) loquuti videantur; apud quos sensim inolevit mos sic loquendi. Sed antiquiores Græci plane contrarium, (grave reputantes in alto et acutum in imo.) Quod etiam ad Boethii tempora continuatum est, qui in schematismis suis, grave semper in summo ponit, et acutum in imo."-David Gregory, in Præfat. ad edit. suam Euclid Op. Oxon. 1703.

The association to which, in modern times, we are habituated from our infancy, between the ideas of acute and high, and between those of grave and low, is accounted for by Dr. Smith, in his Harmonics, from the formation of the voice in singing; which Aristides Quintilianus thus describes: "Firetai de ý μev Bugutys, κατωθεν αναφερομένου του πνεύματος, ἡ δ' οξύτης επιπολής προτεμένου, &c. Et quidem gravitas fit, si ex inferiore parte (gutturis) spiritus sursum feratur, acumen vero, si per summam partem prorumpat;" (as Meibomius translates it in his notes.) See Smith's Harmonics, p. 3.

Dr. Beattie, in his ingenious essay on poetry and music, says it is probable that the deepest or gravest sound was called summa by the Romans, and the shrillest or acutest ima; and he conjectures, that "this might have been owing to the construction of their instruments; the string that sounded the former being perhaps highest in place, and that which sounded the latter lowest." If this conjecture could be verified, it would afford a proof from the fact, how liable the mind is to be influenced in this respect by casual combinations.