These observations we will illustrate by a glance at the theories propounded on the great subject of perception—on the nature of our knowledge of the external world, this visible and tangible creation.
To a plain unsophisticated man, a stranger to the subtleties of metaphysical thought, it appears quite inconceivable, when he is told that the existence of the visible and palpable scene before him should be converted into a problem of apparently invincible difficulty. Yet so it is. The metaphysician first carries off in triumph what are called its secondary qualities, as colour and heat, proving them to be no qualities of matter, but of mind, or the sensitive being. He next assails what had been pronounced to be its primary or essential qualities; the dark tangible mass that he had left behind is not suffered to retain its inert existence; extension, the power to fill space or resist pressure, what are these, he asks, but our own sensations or remembered sensations of touch, which have got associated, embodied together, agglomerated round some occult cause? What, after all, he exclaims, do we know of matter but as a something which possesses certain influences over us?—a something which is utterly unrepresented to us by the senses. And now this word "substance," which formerly expressed a thing so well known, and every moment handled and looked at, is transformed to an invisible, intangible, imperceptible substratum—an unknown upholder of certain qualities, or, in more exact language, an unseen power clothing itself in our attributes—an existence far more resembling what is popularly understood by spirit than by matter. At length, even this unseen substratum is drawn within the world of thought, and becomes itself mere thought. There is no matter, there is no space, save what the mind creates for, and out of itself. Our man of simple apprehension, much bewildered, not at all convinced, breaks from the chain of sophistry, opens wide his eyes, and declares after all that "seeing is believing."
We think so too.
On this subject of perception it is well known that Reid and Stewart, refusing to be drawn into any hypothesis or unsatisfactory analysis, contented themselves with stating, in the preciser language of the schools, the fact as it appears to the plain unsophisticated observer. Reid's explanations are unfortunately mingled up with his controversy against the old hypothesis of ideas or images of things perceived in the mind—an hypothesis combated by him with unnecessary vehemence—but this detracts little from their substantive correctness or utility. This strange notion of images emanating from the external object, entering the mind, and being there perceived, was, after all, in its origin, rather a physical than a metaphysical hypothesis. The ancient speculator upon the causes of things felt, as we feel at this moment, the necessity for some medium of communication between the eye and the distant object, and not having detected this medium in the light which traverses or fills the space between them, he had recourse to this clumsy invention of images or species raying out from the surfaces of things. At the time when Reid wrote, this hypothesis, in its crude form, cannot be said to have existed; but it had left its traces in the philosophical language of the period, and there was certainly a vague notion prevalent that the idea of an object was a tertium quid, a something that was neither the mind nor the object.
We will quote the statement which Dugald Stewart makes of Reid's doctrine of perception. As he himself adopts the statement, it will embrace at once the opinion of both these philosophers:—
"To what, may it be asked, does this statement (of Reid's) amount? Merely to this, that the mind is so formed that certain impressions produced on our organs of sense by external objects, are followed by correspondent sensations, and that these sensations (which have no more resemblance to the qualities of matter, than the words of a language have to the things they denote) are followed by a perception of the existence and qualities of the bodies by which the impressions are made; that all the steps of this progress are equally incomprehensible; and that for any thing we can prove to the contrary, the connexion between the sensation and the perception, as well as that between the impression and the sensation, may be both arbitrary; that it is therefore by no means impossible that our sensations may be merely the occasions on which the correspondent perceptions are excited; and that at any rate the consideration of these sensations, which are attributes of mind, can throw no light on the manner in which we acquire our knowledge of the existence and qualities of body. From this view of the subject, it follows that it is the external objects themselves, and not any species or images of these objects (or, we may add, any mere agglomeration of present and remembered sensations) that the mind perceives; and that although, by the constitution of our nature, certain sensations are rendered the constant antecedents of our perceptions, yet it is just as difficult to explain how our perceptions are obtained by their means, as it would be upon the supposition that the mind were all at once inspired with them, without any concomitant sensations whatever."—(Elements of the Philosophy of the Human Mind, Vol. i. p. 92.)
It is seen here that both Reid and Stewart considered perception as a simple elementary fact or phenomenon of the human mind, and refused their assent to that analysis which would resolve it into sensation, accompanied with certain acts of memory and judgment. This last, however, has been the most popular amongst modern psychologists, who have many of them expressed an extreme impatience at the apparent sluggishness of these veterans in philosophy. We remember the time when we shared the same feeling of impatience, and thought it a most useless encumbrance to maintain this perception amongst the simple elements of the human mind: we now think otherwise, and see reason to acquiesce in the sound judgment, which took up the only safe, though unostentatious position, which this embarrassing subject affords.
Dr Brown, it is well known, departed from his predecessors at this point, and may here be considered as one of the ablest representatives of the sensational school. He expended much ingenuity in his analysis of perception, though in our opinion with very little result. No one saw more distinctly than he, that sensation alone could never give us the idea of an external object, or of space, or any thing external to the mind. No one has more satisfactorily shown that the notion of an extended resisting body, supposed by many to be resolved into the sensations of touch, cannot be derived from this source alone, but must have some other origin than the pure sensation, which is a mere mental phenomenon or state of the consciousness. But he imagined he had overcome the difficulty by introducing to us a new sensation, the muscular, that which we experience when we move our limbs. What he could not derive from the old sense of touch, he thought himself able to deduce from the reasonings of the mind on this muscular sensation; but the same difficulties which he himself so lucidly set forth when treating upon touch, will be found to pursue him here also. This muscular sensation, like every other, is in itself a mere state of the consciousness, begins and ends in a mere pleasure or pain. That it terminates abruptly, and contrary to our volition, in a feeling of resistance, (as when our arm is arrested in its motion,) is saying nothing more than that one sensation gives place to another without our willing it; a statement which might be made in a thousand other cases of sensation with equal propriety. But the author shall explain his own theory.
"The infant stretches his arm for the first time, by that volition without a known object, which is either a mere instinct or very near akin to one; this motion is accompanied with a certain feeling; he repeats the volition, which moves his arm, fifty or one thousand times, and the same progress of feeling takes place during the muscular action. In this repeated progress he feels the truth of that intuitive proposition, which in the whole course of the life that awaits him is to be the source of all his expectations, and the guide of all his actions—the simple proposition that what has been as an antecedent, will be followed by what has been as a consequent. At length he stretches out his arm again, and instead of the accustomed progression, there arises, in the resistance of some object opposed to him, a feeling of a very different kind, which, if he persevere in his voluntary effort, increases gradually to severe pain, before he has half completed the usual progress. There is a difference, therefore, which we may without any absurdity suppose to astonish the little reasoner; for the expectation of similar consequents from similar antecedents, is observable even in his earliest actions, and is probably the result of an original law of mind, as universal as that which renders certain sensations of sight and sound the immediate result of certain affections of our eye or ear. To any being who is thus impressed with belief of similarities of sequence, a different consequent necessarily implies a difference of the antecedent. In the case at present supposed, however, the infant, who as yet knows nothing but himself, is conscious of no previous difference; and the feeling of resistance seems to him, therefore, something unknown, which has its cause in something that is not himself."—(Vol. i. p. 514.)
There is a certain pre-arrangement here of the circumstances to suit the convenience of explanation. The little arm of the infant being very closely fastened to its own little body, it could hardly move it fifty or a thousand times in succession, or even once, without its muscular sensation terminating in the sense of resistance, or pressure, which is but another form of the sense of touch. In short, this would be always sooner or later the consequent upon this muscular sensation. And it appears very evident that "the little reasoner," more especially if he held the same doctrine as Brown on the nature of cause and effect, would look no further than the first sensation for the cause of the second. There would be few instances in his limited experience more marked of invariable antecedence and consequence than this,—that the muscular sensation would sooner or later be followed by a tactual one. If we could suppose it possible, that the infant logician had to make the discovery of an external world by an effort of reasoning upon its sensations, we should say that this case was the least likely of any to lead him to the discovery—the least likely to impel him to look out of the circle of sensations for a cause of them.