This brings us to the evident conclusion that mere sensation has no necessary relation to an external object; for it not only can, but it not unfrequently does, exist without any such object.
This correspondence of the internal to the external belongs to the judgment which accompanies sensation, not to sensation itself.
If brutes refer their sensations to objects, as they probably do, instinct must supply in them the want of judgment, as in the child who has not acquired the use of the intellectual faculties.
Sensation, therefore, in itself considered, affirms nothing. It is a mere affection of our being, an effect produced in our soul, and does not determine whether there is any action of an external object upon our senses, nor whether the object is what it seems to be.
2. Let us imagine an animal reduced to the one sense of touch, and that not developed as in us, but confined to a few rude impressions like those of heat and cold, warmth and dryness; and let us compare it with human sensibility. What an immense distance between the two! Sensibility in such an animal borders on insensibility, whilst in man it approaches intelligence, the representations of his senses are so varied and so extended as to produce within him a whole world, and they might produce infinite others. Man is at the highest round of the ladder, so far as our observation goes, but who can tell how much higher it may be possible to go?
3. However developed and perfected we suppose sensibility, it falls far short of intelligence, from which it must ever remain separated, as from a faculty of a different order. Though we suppose the sensitive faculties capable of indefinite perfectibility, they can never reach the sphere of intelligence, properly so called. This perfectibility would lie in a different order, eternally distinct from that of intellectual beings. If we suppose a color infinitely perfected, it will never become a sound, a sound a taste, a taste a sound, nor a sound a color; because perfectibility is confined to its own order. Therefore, however it may be perfected, sensibility can never become intelligence.
This observation will serve to guard against one of the most fatal errors of our age, which consists in regarding the universe as the result of a mysterious force, which, developing itself by a continual movement, at once spontaneous and necessary, goes on giving birth to beings and elevating species by a perpetual transformation. Thus the greater perfection of the vegetable organization would produce the animal faculties; these being perfected would become sensitive, and in measure as they progressed in the order of sensation they would approach the realm of intelligence, and would finally attain it. There is not a little analogy between this system and that which makes thought a transformed sensation; it effaces the dividing line between intelligent and non-intelligent beings; the sensations of an oyster may, according to it, be so perfected as to be converted into an intelligence superior to that of Bossuet or of Leibnitz; and the development of the faculties of the man-statue would be an emblem of the development of the universe.
4. It may have been already remarked that we are now speaking of the sensitive faculty in itself considered, abstracting from its relations to external objects; and that we therefore comprehend in the word sensation, all affections of the senses, whether actually produced, recollected, or imagined; that is, all affections in all degrees from the first direct consciousness of them, or when they are presented to the being which experiences them, until they reach the limit where intelligence, strictly so called, commences.
It is impossible here to draw the dividing line between the sensible and the intelligible; this requires profound and extensive studies upon sensations compared with ideas, which does not belong to this place: but it will be well to have pointed out the existence of this line, in order to avoid confusion in a most subtle matter, in which every error is attended with the most serious consequences.