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

by Thomas Brown

After our very full discussion of the general phenomena of perception,—as common to all our senses, and as peculiarly modified in the different tribes of our sensations,—I might now quit a subject, to which its primary interest as the origin of our knowledge, has led me to pay, perhaps, a disproportionate attention. But besides the theories, to the consideration of which our general inquiry has incidentally led us, there are some hypothetical opinions on the subject, of which it is necessary that you should know at least the outline,—not because they throw any real light on the phenomena of perception, but because, extravagantly hypothetical as they are, they are yet the opinions of philosophers, whose eminence, in other respects, renders indispensable some slight knowledge even of their very errors.

In reviewing these hypotheses, it will be necessary to call your attention to that doctrine of causation, which I before illustrated at great length, and which I trust, therefore, I may safely take for granted that you have not forgotten.

In sensation, I consider the feeling of the mind to be the simple effect of the presence of the object; or, at least, of some change, which the presence of the object produces in the sensorial organ. The object has the power of affecting the mind; the mind is susceptible of being affected by the object,—that is to say, when the organ, in consequence of the presence of the external object, exists in a certain state, the affection of the mind immediately follows. If the object were absent, in any particular case, the mind would not exist in the state which constitutes the sensation produced by it; and, if the susceptibility of the mind had been different, the object might have existed, as now, without any subsequent sensation. In all this series of mere changes, or affections, in consequence of certain other preceding changes, or affections, though a part of the series be material, and another part mental, there is truly, as I have repeatedly remarked to you, no more mystery than in any other series of changes, in which the series is not in matter and mind successively, but exclusively in one or the other. There is a change of state of one substance, in consequence of a change of some sort in another substance; and this mere sequence of change after change is all which we know in either case. The same Almighty Being, who formed the various substances to which we give the name of matter, formed also the substance to which we give the name of mind; and the qualities with which he endowed them, for those gracious ends which he intended them to answer, are mere susceptibilities of change, by which, in certain circumstances, they begin immediately to exist in different states. The weight of a body is its tendency to other bodies, varying according to the masses and distances;—in this instance, the quality may be said to be strictly material. The greenness or redness ascribed to certain rays of light, are words expressive merely of changes that arise in the mind when these rays are present on the retina; in this case, the quality, though ascribed to the material rays as antecedent, involves the consideration of a certain change of state in the mind which they affect. But the greenness or redness, though involving the consideration both of mind affected, and matter affecting, is not less conceivable by us as a quality of matter than the weight, which also involves the consideration of two substances, affecting and affected, though both go under the name of matter alone. All the sequences of phenomena are mysterious, or none are so.

It is wonderful, that the presence of a loadstone should cause a piece of iron to approach it; and that the presence of the moon, in different parts of the heavens, should be continually altering the relative tendencies of all the particles of our earth. In like manner, it is, indeed, wonderful, that a state of our bodily organs should be followed by a change of state of the mind, or a state of our mind by a change of state of our bodily organs; but it is not more wonderful, than that matter should act on distant matter, or that one affection of the mind, should be followed by another affection of the mind, since all which we know in either case, when matter acts upon matter, or when it acts upon mind, is, that a certain change of one substance has followed a certain change of another substance,—a change which, in all circumstances exactly similar, it is expected by us to follow again. We have experience of this sequence of changes alike in both cases; and, but for experience, we could not, in either case, have predicted it.

This view of causation, however,—as not more unintelligible in the reciprocal sequences of events in matter and mind than in their separate sequences,—could not occur to philosophers while they retained their mysterious belief of secret links, connecting every observed antecedent with its observed consequent; since mind and matter seemed, by their very nature, unsusceptible of any such common bondage. A peculiar difficulty, therefore, as you may well suppose, was felt, in the endeavour to account for their mutual successions of phenomena, which vanishes, when the necessity of any connecting links in causation is shewn to be falsely assumed.

In their views of perception, therefore, as a mental effect produced by a material cause, philosophers appear to have been embarrassed by two great difficulties:—the production of this effect by remote objects,—as when we look at the sun and stars, in their almost inconceivable distances above our heads; and the production of this effect by a substance, which has no common property that renders it capable of being linked with the mind in the manner supposed to be necessary for causation. These two supposed difficulties appear, to me, to have led to all the wild hypotheses that have been advanced with respect to perception.

The former of these difficulties,—in the remoteness of the object perceived,—even though the principle had not been false which supposes, that a change cannot take place in any substance, in consequence of the change of position of a distant object,—a principle, which the gravitation of every atom disproves,—arose, it is evident, from false views of the real objects of perception. It is on this account, that I was at some pains, when we entered on our inquiry into the nature of perception, to shew the futility of the distinction which is made of objects that act immediately on the senses, and those which act on them through a medium,—the medium, in this case, as light in vision, and the vibrating air in sound, being the real object of the particular sense,—and the reference to a more remote object being the result, not of the simple original sensation, but of knowledge previously acquired.

The mistake as to the real object of perception, and the supposed difficulty of action at a distance, must have had very considerable influence in producing the Peripatetic doctrine of perception by species, of which the cumbrous machinery seems to have been little more than a contrivance for destroying, as it were, the distance between the senses and the objects that were supposed to act on them. According to this doctrine, every object is continually throwing off certain shadowy films or resemblances of itself, which may be directly present to our organs of sense, at whatever distance the objects may be, from which they flowed. These species or phantasms,—the belief of the separate existence of which must have been greatly favoured by another tenet of the same school, with respect to form as essentially distinct from the matter with which it is united, were supposed to be transmitted, in a manner, which there was no great anxiety to explain, to the brain and to the mind itself. I need not detail to you the process by which these sensible species, through the intervention of what were termed the active and passive intellect, were said to become, at last, intelligible species, so as to be objects of our understanding. It is with the mere sensitive part of the process, that we have at present any concern; and in this, of itself, there is sufficient absurdity, without tracing all the further modifications, of which the absurdity is capable, if I may speak so lightly of follies that have a name, which, for more than a thousand years, was the most venerable of human names, to pass them current as wisdom,—and which were read and honoured as wisdom by the wise of so many generations.

I cannot pay you so very poor a compliment, as to suppose it necessary to employ a single moment of your time in confuting what is not only a mere hypothesis, (and an hypothesis which leaves all the real difficulties of perception precisely as before,) but which, even as an hypothesis, is absolutely inconceivable. If vision had been our only sense, we might, perhaps, have understood, at least, what was meant by the species, that directly produce our visual images. But what is the phantasm of a sound or an odour? or what species is it, which, at one moment, produces only the feeling of cold, or hardness, or figure, when a knife is pressed against us, and the next moment, when it penetrates the skin, the pain of a cut? The knife itself is exactly the same unaltered knife, when it is merely pressed against the hand, and when it produces the incision; and the difference, therefore, in the two cases, must arise, not from any species which it is constantly throwing off, since these would be the same, at every moment, but from some state of difference in the mere nerves affected.

I fear, however, that I have already fallen into the folly which I professed to avoid,—the folly of attempting to confute, what, considered in itself, is not worthy of being seriously confuted, and scarcely worthy even of being proved to be ridiculous. It must be remembered, however, in justice to its author, that the doctrine of perception, by intermediate phantasms, is not a single opinion alone, but a part of a system of opinions, and that there are many errors, which, if considered singly, appear too extravagant for the assent of any rational mind, that lose much of this extravagance, by combination with other errors, as extravagant. Whatever difficulties the hypothesis of species involved, it at least seemed to remove the supposed difficulty of perception at a distance, and by the half spiritual tenuity of the sensible images, seemed also to afford a sort of intermediate link, for the connexion of matter with mind; thus appearing to obviate, or at least to lessen, the two great difficulties, which I suppose to have given occasion to the principal hypothesis on this subject.