Lectures on the Philosophy of the Human Mind (Vol. 1 of 3)

by Thomas Brown

Though, as I have explained to you fully, in my former Lectures, we should not,—at least in far the greater number of our sensations,—have considered them, originally, as proceeding from external causes, we yet, after the acquisitions of knowledge, with which the first years of our life enrich us, believe, that there is an external cause of all our sensations,—of smells and tastes, as much as of those feelings of the mind, which constitute our notions of extension and resistance. But the difference, in these cases, is, that though we learn, by experience of certain successions or co-existences of feelings, to refer to a corporeal cause our sensations of fragrance, and various other species of sensations, there is nothing in the sensation of fragrance itself, or in the other analogous sensations, of which I speak, that might not indicate as much a cause directly spiritual, as a cause like that to which we at present give the name of body,—while the very notion of extension and resistance combined, seems necessarily to indicate a material cause, or rather is truly that which constitutes our very notion of matter.

We believe, indeed, that our sensations of fragrance, sweetness, sound, have causes of some sort, as truly as we believe, that our feelings of extension and resistance have a cause, or causes of some sort; but if we have previously given the name of matter, with direct reference to the one set of effects, and not with direct reference to the other, it necessarily follows, that, in relation to matter, as often as we speak or think of it, the qualities which correspond with the one set of effects, that have led us to use that name, must be regarded by us as primary, and the others, which may, or may not coexist with these, only as secondary. An external body may, or may not be fragrant, because fragrance is not one of the qualities previously included by us in our definition of a body; but it must be extended, and present an obstacle to our compressing force, because these are the very qualities, which we have included in our definition, and without which, therefore, the definition must cease to be applicable to the thing defined.

If, originally, we had invented the word matter to denote the cause, whatever it might be, of our sensations of smell, it is very evident, that fragrance would then have been to us the primary quality of matter, as being that which was essential to our definition of matter,—and all other qualities, by which the cause of smell might, or might not at the same time affect our other senses, would then have been secondary qualities only,—as being qualities compatible with our definition of matter, but not essential to it.

What we now term matter, however, I have repeatedly observed,—is that which we consider as occupying space, and resisting our effort to compress it; and those qualities of matter may well be said to be primary, by which matter itself, as thus defined, becomes known to us,—or by the union of which, in our conception, we form the complex notion of matter, and give or withhold that name according as these qualities are present or absent. Extension and resistance are the distinguishing qualities that direct us in all our applications of the word which comprehends them. They are truly primary qualities, therefore; since, without our consideration of them, we never could have formed the complex notion of the substance itself, to which we afterwards, in our analysis of that complex notion, ascribe them separately as qualities;—and all the other qualities, which we may afterwards find occasion to refer to an extended resisting substance, must evidently be secondary, in reference to those qualities, without which as previously combined in our thought, we could not have had the primary notion of the substance to which we thus secondarily refer them. If, in the case which we have already frequently imagined, of the single sense of smell, we had been absolutely unsusceptible of every other external feeling, we might, indeed, have considered our sensation as the effect of some cause,—and even of a cause that was different from our mind itself; but it is very evident that we could not have considered it as the effect of the presence of matter, at least as that term is now understood by us. If, in these circumstances,—after frequent repetition of the fragrance, as the only quality of bodies with which we could be acquainted,—we were to acquire in an instant all the other senses which we now possess,—so as to become capable of forming that complex notion of things extended and resisting, which is our present notion of matter, we should then, indeed, have a fuller notion of the rose, of the mere fragrance of which we before were sensible, without knowing of what it was the fragrance, and might learn to refer the fragrance to the rose, by the same coexistences of sensations which have led us, in our present circumstances, to combine the fragrance with other qualities, in the complex conception of the flower. Even then, however, though the fragrance, which was our first sensation, had truly been known to us before the other qualities, and though the sensation, therefore, would deserve the name of primary, the reference of this earlier feeling to the external rose as its cause, would still truly be secondary to the earlier reference, or rather to the earlier combination of other qualities, in one complex whole, by which we had formed to ourselves the notion of the extended and resisting rose, as a body, that admitted the subsequent reference of the delightful sensation of fragrance to be made to it, as the equal cause of these different effects.

In this sense, then, the distinction of the primary and secondary qualities of matter is just,—that, whatever qualities we refer to a material cause must be, in reference, secondary to those qualities that are essential to our very notion of the body, to which the subsequent reference of the other qualities is made. We have formed our definition of matter; and, as in every other definition of every sort, the qualities included in the definition, must always, in comparison of other qualities, be primary and essential, relatively to the thing defined.

Nor is this all.—It will be admitted likewise, that the qualities termed primary,—which alone are included in our general definitions of matter, and which are all, as we have seen, modifications of mere extension and resistance, are, even after we have learned to consider the causes of all our sensations as substances external to the mind, still felt by us to be external, with more clearness and vividness, than the other qualities, which we term secondary. The difference is partly, and chiefly, in the nature of the sensations themselves, as already explained to you, but depends also, I conceive, in no inconsiderable degree, on the permanence and universality of the objects which possess the primary qualities, and the readiness with which we can renew our feeling of them at will, from the constant presence of our own bodily frame, itself extended and resisting, and of the other causes of these feelings of extension and resistance, that seem to be every where surrounding us. Tastes, smells, sounds,—even colours though more lasting than these—are not always before us;—but there is not a moment at which we cannot, by the mere stretching of our hand, produce at pleasure, the feeling of something extended and resisting. It is a very natural effect of this difference, that the one set of causes which are always before us, should seem to us, therefore, peculiarly permanent, and the other set, that are only occasionally present, should seem almost as fugitive as our sensations themselves.

In these most important respects, there is, then, a just ground for the distinction of the primary from the secondary qualities of bodies. They are primary in the order of our definition of matter; and they are felt by us as peculiarly permanent, independently of our feelings, which they seem at every moment ready to awake. The power of affecting us with smell, taste, sight, or hearing, may or may not be present; but the power of exciting the feelings of extension and resistance is constantly present, and is regarded by us as essential to our very notion of matter,—or, in other words, we give the name of matter, only where this complex perception is excited in us. We seem, therefore, to be constantly surrounded with a material world of substances extended and resisting, that is to say, a world of substances capable of exciting in us the feelings which are ascribed to the primary quality of matter;—but still the feeling of these primary qualities, which we regard as permanent, is not less than the feeling of the secondary qualities, a state or affection of the mind, and nothing more;—and in the one case, as much as in the other, in the perception of the qualities termed secondary, as much as of the qualities termed primary, the feeling, when it occurs, is the direct or immediate result of the presence of the external body with the quality of which it corresponds;—or, if there be any difference in this respect, I conceive that our feeling of fragrance, or sweetness, was, originally at least, a more immediate result of the presence of odorous or sapid particles,—than any feeling of extension, without the mind, was the effect of the first body which we touched.

To the extent which I have now stated, then, the difference of these classes of qualities may be admitted. But as to the other differences asserted, they seem to be founded on a false view of the nature of perception. I cannot discover any thing in the sensations themselves, corresponding with the primary and secondary qualities, which is direct, as Dr Reid says, in the one case, and only relative in the other. All are relative, in his sense of the term, and equally relative,—our perception of extension and resistance, as much as our perception of fragrance or bitterness. Our feeling of extension is not itself matter, but a feeling excited by matter. We ascribe, indeed, our sensations as effects to external objects that excite them; but it is only by the medium of our sensations that these, in any case, become known to us as objects. To say that our perception of extension is not relative, to a certain external cause of this perception, direct or indirect, as our perception of fragrance is relative to a certain external cause, would be to say that our perception of extension, induced by the presence of an external cause, is not a mental phenomenon, as much as the perception of fragrance, but is something more than a state of the mind; for, if the perception of extension be, as all our perceptions and other feelings must surely be, a mental phenomenon, a state of mind, not of matter, the reference made of this to an external cause, must be only to something which is conceived relatively as the cause of this feeling. What matter is independently of our perception, we know not, and cannot know, for it is only by our sensations that we can have any connexion with it; and even though we were supposed to have our connexion with it enlarged, by various senses additional to those which we possess at present, and our acquaintance with it, therefore, to be far more minute, this very knowledge, however widely augmented, must itself be a mental phenomenon, in like manner, the reference of which, to matter, as an external cause, would still be relative only like our present knowledge. That the connexion of the feeling of extension, with a corporeal substance really existing without, depends on the arbitrary arrangement made by the Deity; and that all of which we are conscious might, therefore, have existed, as at present, though no external cause had been, Dr Reid, who ascribes to an intuitive principle, our belief of an external universe, virtually allows; and this very admission surely implies, that the notion does not, directly and necessarily, involve the existence of any particular cause, whatever it may be in itself, by which the Deity has thought proper to produce the corresponding feeling of our mind. It is quite evident, that we cannot, in this case, appeal to experience, to inform us what sensations or perceptions are more or less direct; for experience, strictly understood, does not extend beyond the feelings of our own mind, unless in this very relative belief itself, that there are certain external causes of our feelings,—causes which it is impossible for us not to conceive as really existing, but of which we know nothing more than that our feelings, in all that wide variety of states of mind, which we express briefly by the terms sensation or perception, are made to depend on them. In the series of states in which the mind has existed, from the first moment of our life, to the present hour, the feelings of extension, resistance, joy, sorrow, fragrance, colour, hope, fear, heat, cold, admiration, resentment, have often had place; and some of these feelings, it has been impossible for us not to ascribe to a direct external cause; but there have not been in the mental series, which is all of which we can be conscious, both that feeling of the mind which we term the perception of extension, and also body itself, as the cause of this feeling; for body, as an actual substance, cannot be a part of the consciousness of the mind, which is a different substance. It is sufficient for us to believe, that there are external causes of this feeling of the mind, permanent and independent of it, which produce in regular series, all those phenomena that are found by us in the physical events of the universe, and with the continuance of which, therefore, our perceptions also will continue; we cannot truly suppose more, without conceiving our very notion of extension, a mental state, to be itself a body extended, which we have as little reason to suppose, as that our sensation of fragrance, another mental state, is itself a fragrant body. It is needless to prolong this discussion, by endeavouring to place the argument in new points of view. The simple answer to the question, “Is our notion of extension, or of the other primary qualities of matter, a phenomenon or affection of matter or of mind?” would be of itself sufficient; for if it be a state of the mind, as much as our feeling of heat or of fragrance, and a state produced by the presence of an external cause, as our sensations of heat or fragrance are produced, then there is no reason to suppose, that the knowledge is, in one case, more direct than in the other. In both, it is the effect of the presence of an external cause, and in both it must be relative only,—to adopt Dr Reid's phrase,—to that particular cause which produced it; the knowledge of which cause, in the case of extension, as much as in the case of fragrance, is nothing more than the knowledge, that there is without us, something which is not our mind itself, but which exists, as we cannot but believe, permanently and independently of our mind, and produces according to its own varieties, in relation to our corporeal frame at one time, that affection of the mind which we denominate the perception of extension; at another time, that different affection of the mind, which we denominate the perception of fragrance. What it is, as it exists in absolute independence of our perceptions, we who become acquainted with it, only by those very perceptions, know not, in either case; but we know it at least,—which is the only knowledge important for us,—as it exists relatively to us; that is to say, it is impossible for us, from the very constitution of our nature, not to regard the variety of our perceptions, as occasioned by a corresponding variety of causes, external to our mind; though, even in making this reference, we must still believe our perceptions themselves, to be altogether different and distinct from the external causes, whatever they may be, which have produced them; to be, in short, phenomena purely mental, and to be this equally, whether they relate to the primary or the secondary qualities of matter; our notion of extension, in whatever way the Deity may have connected it with the presence of external things, being as much a state of the mind itself, as our notion of sweetness or sound.

These observations, on the process of suggestion, which, in the reference to an external cause, distinguishes our perceptions from our simpler sensations,—and on the real and supposed differences of the primary and secondary qualities of matter,—will have prepared you, I trust, for understanding better the claim which Dr Reid has made to the honour of overthrowing what he has termed the ideal system of perception. It is a claim, as I have said, which appears to me truly wonderful, both as made by him and admitted by others; the mighty achievement which appeared to him to be the overthrow of a great system, being nothing more, than the proof that certain phrases are metaphorical, which were intended by their authors to be understood only as metaphors.