If this simple and eternal substance enjoys the same properties as the souls which are lodged in the sagest brains, it ought to reason like them. Why does it not? If my madman sees a thing red, while the wise men see it blue; if when my sages hear music, my madman hears the braying of an ass; if when they attend a sermon, he imagines himself to be listening to a comedy; if when they understand yes, he understands no; then I conceive clearly that his soul ought to think contrary to theirs. But my madman having the same perceptions as they have, there is no apparent reason why his soul, having received all the necessary materials, cannot make a proper use of them. It is pure, they say, and subject to no infirmity; behold it provided with all the necessary assistance; nothing which passes in the body can change its essence; yet it is shut up in a close carriage, and conveyed to Charenton. This reflection may lead us to suspect that the faculty of thought, bestowed by God upon man, is subject to derangement like the other senses. A madman is an invalid whose brain is diseased, while the gouty man is one who suffers in his feet and hands. People think by means of the brain, and walk on their feet, without knowing anything of the source of either this incomprehensible power of walking, or the equally incomprehensible power of thinking; besides, the gout may be in the head, instead of the feet. In short, after a thousand arguments, faith alone can convince us of the possibility of a simple and immaterial substance liable to disease. The learned may say to the madman: "My friend, although deprived of common sense, thy soul is as pure, as spiritual, and as immortal, as our own; but our souls are happily lodged, and thine not so. The windows of its dwelling are closed; it wants air, and is stifled." The madman, in a lucid interval, will reply to them: "My friends, you beg the question, as usual. My windows are as wide open as your own, since I can perceive the same objects and listen to the same sounds. It necessarily follows that my soul makes a bad use of my senses; or that my soul is a vitiated sense, a depraved faculty. In a word, either my soul is itself diseased, or I have no soul." One of the doctors may reply: "My brother, God has possibly created foolish souls, as well as wise ones." The madman will answer: "If I believed what you say, I should be a still greater madman than I am. Have the kindness, you who know so much, to tell me why I am mad?" Supposing the doctors to retain a little sense, they would say: "We know nothing about the matter." Neither are they more able to comprehend how a brain possesses regular ideas, and makes a due use of them. They call themselves sages, and are as weak as their patient.