Much as H•tuthon has labored to elucidate this doctrine in all its bearings, it has not been universally accepted as satisfactory. 3Iany believe that lie has regarded as an ulti mate fact of our constitution what admits of being still further, resolved,. and has mis taken an acquisition of the mature mind for a primitive or instinctive revelation.
Professor Ferrier, in his Institutes of _Metaphysic, has gone through the question with extraordinary minuteness mid elaboration. His main position is the inseparability of the subject and the object in perception (a position also maintained by Hamilton in the above extract) which is not reconcilable with the common assumption as to the independent existence of matter. Indeed, lie reduces the received dogma of the existence of matter per se to a self-contradiction, and builds up a system in strict conformity with the corre lation, or necessary connection, of the mind perceiving with the object perceived. He thus approaches nearer to Berkeley than to Hamilton or to Reid.
Those who would endeavor to show that our notion of the outer world is a complex fact. and an acquisition; and not a simple apprehension of the uneducated mind, explain themselves to the following effect. It is in the exercise of force that we have to look for the peculiar feeling of the externality of sensible things, or the distinction that we make between what impresses from without, and impressions not recognized as outward. Any impression that rouses a stroke of energy within us, and that varies exactly and con stantly as that energy varies, we call an outward impression. Dr. Johnson refuted Berkeley, as lie thought, by kicking a stone. But in fact it was his own action with its consequences, and not the optical impression of a stone in the eye, that satisfied him as to the existence of something outward. The sum total of all the occasions for putting forth active energy, or for conceiving this as possible to be put forth, is our external world.
We experience certain uniformly recurring sensations, and certain uniform changes in these, when we exert particular energies. Thus the visible picture of our dwelling is a permanent and habitual experience, and the variations of appearance that it is sub ject to correspond principally to our own conscious movements. As we move from one end of a room to another, we experience a change of the visible aspect at every step, and this regularly happens as often as we repeat the movement. But at times the appearance exists in another shape, to which we give the name of memory or idea. We draw a marked distinction between these two modes of presentation, the actual and the ideal, and we assign a superiority to the one aver the other. The superiority we find connects itself with the relation to our own movements; a mere idea or mental picture remains the sairlii whatever be our bodily position or bodily exertions; the sensation that we call the actual is entirely at the mercy of our movements, shifting in every possible way (but uniformly), according to the varieties of action that we go through. With a forward movement the visible impression enlarges, with a backward movement it diminishes. A certain movement of the eye shuts it. out, another restores it. The raising of the bead and the bending of the body are followed by an altered spectacle. We eilllnOt but draw
a broad distinction between the mental scenery that is thus shifted by all our move ments. and the ideas and dreams that vary of themselves while we are still. To express the one fact, we use the terms externality, the material world, independent existence; to express the other we employ the opposite language, internality, the world of mind, etc. Even if sensation were only in ourselves, we should still have to distinguish between present sensation and remembered or revived sensation, the reference of the one to our voluntary movements, and of the other to no such modifying causes, would oblige us to note a vital difference in the two classes of facts. Such is the uniformity of connection between certain appearances and certain movements, that we come to anticipate the one through the other. We know that in some one position, as when lying in bed, certain movements of the limbs nail back will bring us to the sensation of a solid contact in the feet; that another series of movements will bring on a particular view to the sight; that a third movement will give the sound of a bell in the car, and so forth. We canuot avoid regarding those various sensible effects, brought uniformly into play by a regular series of waking voluntary actions, as totally different from our ideas, recollections, and dreams. • As our belief in the externality of the causes of our sensations means that certain actions of ours will bring the sensations into play, or modify•them in a known manlier, this belief is readily furnished by experience, and is no more than our experience entitles its to entertain. When we have been repeatedly' conscious (lint a tree becomes larger mid larger to the eye in connection with a definite locomotion on our part, called the forward advanee; tint this movement brings on at last a sensation of timch; that this sensation of touch varies with definite movements of the arms. and so on; the repetition of all this train of experience fixes it on the mind, so that from one thing alone, as from the distant vision of the tree, we can anticipate, or as it is otherwise called, perceire all the other consequences. We then know, without going through the steps, that the specified movements will bring about all the sensations above described. and we know nothing else; this knowledge, however, is to us the recognition of external existence, the fact that is meant when a material world is spoken of. Belief in external reality is•the sure anticipation of certain sensations on the performance of certain move ments; everything else said to be implied in it is but a convenient hypothesis for aiding the mind in holding together those multifarious connections that our experience has established in the mind. In order to account for the fact that the conscious movement: of elevating the upper eyelid is followed with the sensation of light, to us and to other minds, we suppose a luminous agency always existing even when not affecting us or •ithy other person: we cannot know or verify this supposition—it is a generalization founded upon particular experiences, and serving to sum up those experiences in a con venient form, but no such perennial independent, substance can be absolutely prOved.