Philosophical Musings by T L Hurst

Philosophical Musings
by T L Hurst

Turing Machines and the Chinese Room

Searle's 1980 paper "Minds, Brains and Programs"1 has been the subject of much discussion by researchers into AI, as it suggested that the expectations of strong AI at the time were highly over-optimistic. We take a look at Searle's argument and some prominent replies, but first we need to discuss the Turing test and Turing machines, as these are fundamental to the argument...

The Turing Test

The Turing test2 is a test of a machine's ability to exhibit intelligent behaviour. There are a number of variants, but the idea is for two hidden subjects to converse via a computer keyboard and screen for a fixed period of time. A judge can see the comments made by both, and has to decide which is human. If the judge cannot reliably distinguish a machine from a human being, the machine is said to have passed the test. However, I would suggest that there are, at least, two different ways of succeeding in the test:

  1. By strategies designed to conceal the fact that the computer does not actually understand the input from the other subject (i.e. by subterfuge on the part of the programmers).
  2. By enabling the computer to understand the semantic content of the conversation, so that it actually makes semantically appropriate responses.

Note: So far, it seems that computers which have "passed" the Turing test have done so by using subterfuge. However it does not necessarily follow that computers cannot understand semantic content. Indeed it is arguable that computers do already have a limited form of "understanding", in the sense that they can, and do, respond semantically correctly to their machine language. That functionality is hard coded in the CPU (central processing unit). Hence it may be argued that a machine without a processing unit of some sort is necessarily incapable of passing the Turing test.

Turing Machines

Turing machines3 are abstract descriptions of the most basic elements of a computational device. Practical Turing machines may be constructed from sundry items such as stones and toilet rolls, and although, in principle, a Turing machine can perform any task that a digital computer can, we need to bear in mind that not all Turing machines are equal:


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