Inability will every one find in himself who shall go about to fashion in his understanding any simple idea, not received by his senses from external objects, or by reflection from the operations of his mind about them.
There is no sense that has not a mighty dominion, and that does not by its power introduce an infinite number of knowledges. If we were defective in the intelligence of sounds of musick, and of the voice, it would cause an imaginable confusion in all the rest of our science. For, besides what appertains to the proper effect of every sense, how many arguments, consequences, and conclusions do we draw to other things by comparing one sense with another? Let an understanding man imagine human nature originally producd without the sense of seeing, and consider what ignorance and trouble such a defect would bring upon him, what a darkness and blindness in the soul; he will then see by that, of how great importance to the knowledge of truth the privation of such another sense, or of two or three, should we be so deprivd, would be. We have formd a truth by the consultation and concurrence of our five senses, but peradventure we should have the consent and contribution of eight or ten to make a certain discovery of our own being. The sects that controvert the knowledge of man, do it principally by the incertainty and weakness of our senses.
Michel de Montaigne: Essays, Cottons 3d ed., ch. lxix.