Return to APA Newsletters IndexThe following appeared in Volume 97, Number 2 (Spring, 1998) of the APA Newsletters
The Alan Turing Home Page
http://www.wadham.ox.ac.uk/~ahodges/Turing.html and
http://www.turing.com/turing/Turing.html
Andrew Hodges
Reviewed by:
James H. FetzerThis web site, which is maintained by Andrew Hodges, author of Alan Turing: The Enigma, provides a largely but not entirely biographical introduction to the work of Alan Turing (1912-54), a brilliant mathematician whose (posthumous) entitlement to the title of Founder of Computer Science (and perhaps of Artificial Intelligence as well) is persuasively argued on its pages. Although beginning students are likely to be the principal beneficiaries of this web site, there is enough material on sophisticated topics (such as morphogenesis-the theory of patterns of biological growth) to appeal to more advanced students. And appropriate links to numerous other web sites are conveniently provided.
[Review Editor's note: The Turing Home Page is part of a larger collection of internet sites called "The Virtual Museum of Computing," hosted by Oxford University Computing Services. There are other virtual museums, which are parts of a larger, international project to develop a WWW Virtual Library.
Perhaps the most interesting aspect of Turing's life (as it is reported here) revolves about his relationship with Christopher Morcom from 1928 to 1930, when Turing was 16 to 18 years old. Morcom's abrupt death (whose cause is unspecified here) apparently led Turing to think seriously about the human mind and especially how minds-Christopher's mind, in particular-are related to human bodies and whether they might continue to endure after death. This preoccupation, Hodges implies, may have motivated some of his most important conjectures, which concern the nature of the mind and its physical embodiment.
Hodges elaborates the closely-related theme that his homosexuality, which he openly accepted by 1932 and thereafter never sought to conceal, exerted an important influence upon Turing's career, with less damaging consequences as a scholar in England but more adverse effects during the Cold War. Collaboration between the British and the Americans brought U.S. security standards into play, according to which homosexuals were perceived as "security risks" on the basis of their sexual orientation alone. It was his arrest and trial in Manchester for a sexual relationship with a young man, about which he was wholly unapologetic, however, that apparently contributed to his suicide by cyanide on 7 June 1954.
Without doubt, Turing's most important research concerned the limitations of proof within mathematics, where Turing proposed that the boundaries of the computable (of mathematical problems whose solutions were obtainable on the basis of finite applications of finite rules) were co-extensive with those that can be solved using a specific kind of machinery, which consists of an arbitrarily long segmented tape and a device capable of four operations upon that tape, namely: making a mark, removing a mark, moving one segment forward, moving one segment backward. (The state of the tape before a series of operations is applied may be referred to as "input", the state of the tape after it has been applied as "output", and the series of instructions as a "program".)
Using the concept of such machines (now known as "Turing machines"), Turing proved that there are mathematical problems for which no finitistic or computable solutions exist. Similar results relating effective procedures to computable problems were more or less concurrently obtained by Alonzo Church, whose publication in 1936 compelled Turing to refer to Church's earlier paper. As Hodges remarks, however, Church's work was based upon purely mathematical assumptions, while Turing's work appealed to a specific kind of machine, which provided an abstract model for the physical embodiment of the procedures that suitably define "computers" and laid a foundation for the theory of computing. [Review Editor's note: The Alan Turing Home Page includes a link to another site with an interactive simulation of Turing machines written in the Java programming language.]
Turing also argued that such procedures impose limits upon human thought, where (in Hodges' own language), "This triple correspondence between logical instructions, the action of the mind, and a machine which could in principle be embodied in a practical physical form, was Turing's definitive contribution." It should be apparent that Turing thus introduced what has come to be known as the computational conception, according to which thinking is reasoning, reasoning is reckoning, reckoning is computation, and the boundaries of computability define the boundaries of thought. In conjunction with the elaboration of (what is now known as) the Turing test, this formulation suggests that Turing may be equally well entitled to be known as the Founder of AI or of Cognitive Science. Hodges includes many links related to recent experimental computer programs inspired by the Turing Test.
Turing's contributions were not purely theoretical, but included research on cryptanalytic problems, especially decoding the Enigma cipher used by Germany during World War II. In conjunction with research by W. G. Welchman, another Cambridge mathematician, the "Bomba" machine was devised, which provided a mechanical means for decoding German messages. Turing not only contributed to winning the war but also to establishing the feasibility of large-scale, digital-electronics technology. While recent research by John Searle (1992), by Carol Cleland (1993 and 1995), and by others (Fetzer 1994 and 1997) tends to suggest that thinking and computing are not the same thing, there can be little doubt that Turing's contributions to the foundations of computer science are secure.
References
Cleland, C. (1993). "Is the Church-Turing Thesis True?", Minds And Machines, 3 (1993), pp. 283-312.
Cleland, C. (1995). "Effective Procedures and Computable Functions", Minds And Machines, 5 (1995), pp. 9-23.
Fetzer, J. H. (1994). "Mental Algorithms: Are Minds Computational Systems?", Pragmatics And Cognition, 2 (1994), pp. 1-29.
Fetzer, J. H. (1997). "Thinking and Computing: Computers as Special Kinds of Signs", Minds And Machines, 7 (1997), pp. 345-364.
Searle, J. (1992). The Rediscovery Of The Mind. Cambridge, MA: The MIT Press, 1992.
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