Monday, October 30, 2006

The Systems Reply

Take a Turing Machine that takes as input a story in Chinese, followed by a set of questions in Chinese. It is constructed to produce, as output, answers to the questions, in Chinese. The answers are meant to be coherent responses to the questions. The Turing Machine is so well constructed that a native Chinese speaker will believe the responses come from a Chinese speaker.

We might think the Turing Machine understands Chinese.

Take a man, who doesn't speak any Chinese, sitting in a room. He's given a story in Chinese as input, a set of questions in Chinese, and a set of instructions on how to produce, as output, answers in Chinese. The answers are meant to be coherent responses to the questions. The man in the room performs the instructions so well that a native Chinese speaker will believe the responses come from a Chinese speaker.

The man sitting in the room does not understand Chinese.

The Turing Machine is a symbol manipulator. So is the man in the Chinese Room. So, the argument goes: if you accept that the man doesn't understand Chinese, then you must accept that the Turing Machine also does not understand Chinese.

The Systems Reply: while the man in the room does not understand any Chinese, the system taken as a whole does. The system consists of the man and his instructions, presumably in the form of "bits of paper," and perhaps a pen or pencil.

Searle says that arguing that the "conjunction" of the man with the "bits of paper" is capable of understanding, where the man alone is not, is absurd; he feels embarrassed to formulate a response to it at all.

The Turing Machine described above had its instructions - the rules by which it changed from one state to the next - built into its hardware. In the case of this Turing Machine, the Turing Machine itself was the system. The system consisted of: the tape head, and strip of paper on which it marked symbols. We wouldn't say that the tape head or the strip of paper is what understood Chinese, but the Turing Machine taken as a whole system that does.

The system in the Systems Reply, on the other hand, consisted of the man (and all of his constituent parts) and some "bits of paper." So it does seem different than the Turing Machine: it's easier to think of the TM as a single system that can be said to understand than it is to think of the man along with some "bits of paper" and a pencil as one. The TM, after all, is a single machine.

Let's tighten the analogy then. Take a Universal Turing Machine. As input it can take a description of any other Turing Machine, and run it. [Dennett and Hofstadter call this emulation to distinguish it from simulation. Emulation is exact since we keep a description of the emulated machine down to its lowest level states, unlike simulation which is an approximation which attempts to mimic the behavior of that which is simulated.] We feed as input to the Universal Turing Machine an encoding of the Turing Machine described above - the one that can produce output in Chinese so well that Chinese speakers will believe the output was written by a Chinese speaker. The rest of the story is the same: we the feed the UTM some text in Chinese, followed by some questions, and it produces as output Chinese text.

We might think that the Universal Turing Machine, taken together with the encoding of the Turing Machine that can produce Chinese output, understands Chinese.

The idea that the physical machine, the Universal Turing Machine, taken with some "bits of paper" as input (the encoding of the TM that produces Chinese output) does not seem absurd.

An the analogy is tighter: the UTM is analogous to the man sitting in the room; the "bits of paper" are analogous to the encoded Turing Machine.

Dennett says that Searle's argument is a mere "intuition pump" - there is no argument, only an attempt to play on our intuitions. Most people's first intuition is that taking the man with the paper as a system that is capable of understanding is absurd.

I claim that those same people would not find the idea of the Universal Turing Machine along with the encoded Turing Machine that produces Chinese output, as a system that can understand Chinese absurd. It's perfectly intuitive.

If you accept that the UTM taken together with the encoded TM can understand Chinese, you have to accept that the man taken with the bits of paper does too.

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