anything common, in the matter of quality, between an elementary visual sensation and a tactile sensation, since they belong to two different genera? The correspondence between visual and tactile extension can only be explained, therefore, by the parallelism of the order of the visual sensations with the order of the tactile sensations. So we are now obliged to suppose, over and above visual sensations, over and above tactile sensations, a certain order which is common to both, and which consequently must be independent of either. We may go further: this order is independent of our individual perception, since it is the same for all men, and constitutes a material world in which effects are linked with causes, in which phenomena obey laws. We are thus led at last to the hypothesis of an objective order, independent of ourselves; that is to say, of a material world distinct from sensation.
We have had, as we advanced, to multiply our irreducible data, and to complicate more and more the simple hypothesis from which we started. But have we gained anything by it? Though the matter which we have been led to posit is indispensable in order to account for the marvellous accord of sensations among themselves, we still know nothing of it, since we must refuse to it all the qualities perceived, all the sensations of which it has only to explain the correspondence. It is not, then, it cannot be, anything of what we know, anything of what we imagine. It remains a mysterious entity.
