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the experiments by himself. He carried a little card which said on it, “I am deaf-blind. May I put my hand on your face?” so, if he got lost, if somebody would let him do that, he could communicate with them. And he lived a pretty normal life.
    One very striking fact was that all of the cases that succeeded were people who had lost their sight and hearing at about eighteen months old or older—it was primarily through spinal meningitis in those days. People who were younger than that when they became deaf-blind never learned language. There weren’t enough cases to actually prove anything, so the results of the study were never published, but this was a pretty general result. Helen Keller fits. She was twenty months old when she lost her sight and hearing. It suggests, at least, that by eighteen or twenty months, a tremendous amount of language is already known. It can’t be exhibited but it’s in there somewhere, and can possibly be teased out later.
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    It’s known that the ability to acquire language starts decreasing rather sharply by about the mid-teens.
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    That’s descriptively correct, although, again, it’s not 100 percent correct. There is individual variation. There are individuals who can pick up a language virtually natively at a much later age. Actually, one of them was in our department. Kenneth Hale, one of the great modern linguists, could learn a language like a baby. We used to tease him that he just never matured.
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    That’s an exception?
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    Yes. By and large, what you said is true. The basis is not really known, but there are some thoughts about it. One thing we know is that, from the very beginning, brain development entails losing capacities. Your brain is originally set up so that it can acquire anything that a human can acquire. In the case of language, say, it’s set up so that you can acquire Japanese, Bantu, Mohawk, English, whatever. Over time that declines. In some cases, it declines even after a few months of age. What’s happening across all cognitive capacities, not only in the case of language, is that synaptic connections, connections inside the brain, are being lost. The brain is being simplified, it’s being refined. Certain things are becoming more effective, other things are just gone. There’s apparently a lot of synaptic loss around the period of puberty or shortly beforehand, and that could be relevant.
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    I attended one of your seminars in linguistics here at MIT a few years ago, and I was struck by a couple of things. First of all, I was one of the few non-Asians in your class. It was mostly South Asians and East Asians. But the other thing was the extent to which math was involved. You were constantly writing formulas on the blackboard.
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    We should be clear about that. It’s not deep mathematics. It’s not like proving hard theorems in algebraic topology or something. But there’s good reason why some sophistication in mathematics is at least advantageous, maybe necessary, for advanced work. The basic reason is that language is a computational system. So whatever else it is, the capacity we’re both using and sharing is based on a computational procedure that forms an infinite array of hierarchically structured expressions.
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    A lot of people conflate linguistics with the ability to speak many languages. So in your case, people think, Oh, Chomsky, he must know ten or twelve languages. But in fact linguistics is another universe. Explain why the study of language is important. Clearly, you’re animated by it. You’ve devoted most of your life to it.
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    I should say, sometimes there’s a distinction made between languist and linguist. A languist is somebody who can speak a lot of languages. A linguist is somebody who is interested in the nature of language.
    Why is it interesting? Think about the picture that I presented before, which I think is fairly uncontroversial.