PROP. XXII.————
this case, is himself-seeing-the-tree. But he might possibly have a cognisance of the tree, though his seeing of it were exchanged for some other sense. He might apprehend it by the way of touch. Therefore seeing is not absolutely essential to all cognition of the tree. Again, he might possibly have a cognisance of the tree though his touch were exchanged for some other sense. He might hear the rustling of its leaves. Therefore the sense of touch is not absolutely essential to all cognition of the tree. Again, he might still have some cognisance of it though his hearing were exchanged for some other sense. He might smell the fragrance of its blossoms. Therefore hearing is not absolutely essential to all cognition of the tree. Again, he might still have some cognisance of it though his sense of smell were exchanged for some other mode of apprehension. He might apprehend it through the sense of taste. Therefore the sense of smell is not absolutely essential to all cognition of the tree. In short, one and all of our present senses might be abolished, and, provided they were replaced by a set of different sense; our knowledge of the tree might be as perfect or more perfect than it now is. The senses therefore are conditions of cognition wholly contingent, and subject to possible variation; and hence, also, all that is made known to us through their means is wholly contingent, and subject to possible variation.
