I. The internal affection which we call _seeing_. On this point all doubt is impossible. Whether I am asleep or awake, raving or in my sober senses, whether the ornaments are alike or unlike, whether, in fine, they exist or not, there still exists in my soul the representation which I call _seeing the ornaments_. II. I also at the same time form a judgment that, besides the internal affection which I experience, the ornaments exist, that they are in relief, and that they are before my eyes. In this judgment I may be deceived; for I may be asleep or in a delirium; it may be that the ornaments are behind me, and that I only see their reflection in a mirror; it may be that what I see is only a paper placed in such a manner behind a glass, as to make upon the retina of my eyes the same impression as the ornaments would if they were really present; or, finally, it may all be the work of a skilful painter who has given this illusory appearance to his canvas. From this we see that, admitting the existence of the internal fact of sensation, it is possible: I. That there is no external object. II. That the objects exists, but not in the position supposed. III. That the object is not the architectural ornaments. IV. That both are plane surfaces; or, that one is in relief, and the other a plane. 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?