In the "Oxford Companion to the Mind" in the section "Blindness, recovery from", the empiricist John Locke is said to have wondered in 1690: what would happen to a man who, having been blind his whole life, had his vision repaired? If a blind man had learned to distinguish a cube and a globe by touch, could he, once made to see, identify them just by looking at them? The "Oxford Companion to the Mind" goes on to give this touching account of a boy who actually went through this experience: "These remained interesting speculations, until in 1728 an unusually expert and thoughtful surgeon, William Cheselden, reported such a clinical case. Though generally distinguished as a surgeon his achievements were especially ophthalmic operations for cataract [...]. In a celebrated case Cheselden gave sight to a boy aged thirteen or fourteen who was born with highly opaque cataracts. Cheselden reported that:"

When [the boy] first saw, he was so far from making any judgment of distances, that he thought all object whatever touched his eyes (as he expressed it) as what he felt did his skin, and thought no object so agreeable as those which are smooth and regular, though he could form no judgment of their shape, or guess what it was in any object that was pleasing to him: he knew not the shape of anything, nor any one thing from another, however different in shape or magnitude; but upon being told what things were, whose form he knew before from feeling, he would carefully observe, that he might know them again; and (as he said) at first learned to know, and again forgot a thousand things in a day. One particular only, though it might appear trifling, I will relate: Having often forgot which was the cat, and which the dog, he was ashamed to ask; but catching the cat, which he knew by feeling, he was observed to look at her steadfastly, and then, setting her down, said, So, puss, I shall know you another time. He was very much surprised, that those things which he had liked best, did not appear most agreeable to his eyes, expecting those persons would appear most beautiful that he loved most, and such things to be most agreeable to his sight, that were so to his taste. We thought he soon knew what pictures represented, which were [shown] too him, but we found afterwards we were mistaken; for about two months after he was couched, he discovered at once they represented solid bodies, when to that time he considered them only as party-coloured planes, or surfaces diversified with variety of paint; but even then he was no less surprised, expecting the pictures would feel like the things they represented, and was amazed when he found those parts, which by their light and shadow appeared now round and uneven, felt only flat like the rest, and asked which was the lying sense, feeling or seeing?

Being [shown] his father's picture in a locket at his mother's watch, and told what it was, he acknowledged the likeness, but was vastly surprised; asking, how it could be, that a large face could be expressed in so little room, saying, it should have seemed as impossible for him, as to put a bushel of anything into a pint. At first he could bear but very little light, and the things he saw, he thought extremely large; but upon seeing things larger, those first seen he conceived less, never being able to imagine any lines beyond the bounds he saw; the room he was in, he said, he knew to be but part of the house, yet he could not conceive that the whole house could look bigger. Before he was couched, he expected little advantage from seeing, worth undergoing an operation for, except reading and writing; for he said, he thought he could have no more pleasure in walking abroad than he had in the garden, which he could do safely and readily. And even blindness, he observed, had this advantage, that he could go anywhere in the dark, much better than those who can see; and after he had seen, he did not soon lose this quality, nor desire a light to go about the house in the night. He said, every new object was a new delight; and the pleasure was so great, that he wanted words to express it; but his gratitude to his operator he could not conceal, never seeing him for some time without tears of joy in his eyes, and other marks of affection. [...]

If knowledge came to us through the senses, the boy would immediately have been able to visually understand and distinguish shapes. Things we take for granted --- depth perception, for example --- are complex and learned concepts. The boy had to first learn how to use his newfound vision before he could learn anything else from it. Knowledge of how to use the senses is neither encoded genetically, nor can it possibly come from the senses. So where does it come from? Once he got better at using his vision, he could learn from it by using it as an error correction device. That's what senses are: error correction devices. We use them after creatively conjecturing solutions to problems, such as when the boy picked up his pet to test whether it was a cat or a dog through touch. If he ever forgot, it would take more error correction, until he got so good at it he knew. Something that seems as simple as learning to see represents a mountain of problems. Solving them is an impressive creative feat. Remarkably, young children do all of this joyfully and, it seems, effortlessly.

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