Logic Theorist
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Logic Theorist is a computer program written in 1955 by Alan Newell, Herbert Simon and J. C. Shaw. It was the first program deliberately engineered to mimic the problem solving skills of a human being and is called "the first artificial intelligence program."[1] It would eventually prove 38 of the first 52 theorems in Russell and Whitehead's Principia Mathematica, and find new and more elegant proofs for some.[2]
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[edit] History
In 1955, the field of artificial intelligence did not yet exist.[3] Herbert Simon was a political scientist by training and had already produced classic work in the study of how bureaucracies function as well as developed his theory of bounded rationality, for which he would later win a Nobel prize. This work may seem, on the surface, to be very different from artificial intelligence, but it requires the same insight into the nature of human problem solving and decision making. Simon remembers consulting at RAND in the early 1950s and seeing a printer typing out a map, using ordinary letters and punctuation as symbols. He realized that a machine that could manipulate symbols could just as well simulate decision making and possibly even the process of human thought.[4]
The program that printed the map had been written by Alan Newell, a RAND Corporation scientist studying logistics and organization theory. For Newell, the decisive moment was in 1954 when Oliver Selfridge came to RAND to describe his work on pattern matching. Watching the presentation, Newell suddenly understood how the interaction of simple, programmable units could accomplish complex behavior, including the intelligent behavior of human beings. "It all happened in one afternoon," he would later say. [5]
Newell and Simon began to talk about the possibility of teaching machines to think. Their first project was a program that could prove mathematical theorems like the ones used in Bertrand Russell and Alfred North Whitehead's Principia Mathematica. They enlisted the help of computer programmer J. C. Shaw, also from RAND, to develop the program. The first version was hand-simulated: they wrote the program onto 3x5 cards and, as Simon recalled:
In January 1956, we assembled my wife and three children together with some graduate students. To each member of the group, we gave one of the cards, so that each one became, in effect, a component of the computer program ... Here was nature imitating art imitating nature.[6]
They succeeded in showing that the program could successfully prove theorems as well as a talented mathematician. By the summer of 1956, Shaw was able to run the program on the computer at RAND's Santa Monica facility.
That same summer, John McCarthy, Marvin Minsky, Claude Shannon and Nathan Rochester organized a conference on the subject of "artificial intelligence" (a term coined by McCarthy for the conference). Newell and Simon presented the group with the Logic Theorist. However, the program received a lukewarm reception. Simon confides that "we were probably fairly arrogant about it all"[7] and adds:
They didn't want to hear from us, and we sure didn't want to hear from them: we had something to show them! ... In a way it was ironic because we already had done the first example of what they were after; and second, they didn't pay much attention to it.[8]
Logic Theorist soon proved 38 of the first 52 theorems in chapter 2 of the Principia Mathematica. The proof of theorem 2.85 was actually more elegant than the proof produced laboriously by hand by Russell and Whitehead, and Simon was able to show the new proof to Bertrand Russell himself.[9]
Newell and Simon formed a lasting partnership, founding one of the first AI laboratories at Carnegie Tech and developing a series of influential artificial intelligence programs and ideas, including GPS, Soar, and their unified theory of cognition.
[edit] Logic Theorist's influence on AI
Logic Theorist introduced several concepts that would be central to AI research:
- Reasoning as search
- Logic Theorist operated a search tree: the root was the initial hypothesis, each branch was a deduction based on the rules of logic. Somewhere "up" the tree was the goal: the proposition the program intended to prove. The pathway along the branches that led to the goal was a proof -- a series of statements, each deduced using the rules of logic, that led from the hypothesis to the proposition to be proved.
- Heuristics
- Newell and Simon realized that the search tree would grow exponentially and that they needed to "trim" some branches, using "rules of thumb" to determine which pathways were unlikely to lead to a solution. They called these ad-hoc rules "heuristics", using a term introduced by George Polya in his classic book on mathematical proof, How to Solve It. (Alan Newell had taken courses from Polya at Stanford)[10] Heuristics would become an important area of research in artificial intelligence and remains an important method to overcome the intractable combinatorial explosion of exponentially growing searches.
- List processing
- To implement Logic Theorist on a computer, the three researchers developed a programming language, IPL, which used the same form of symbolic list processing that would later form the basis of John McCarthy's Lisp programming language, still the most important language used by AI researchers.[11]
[edit] Philosophical implications
Simon famously told a graduate class in January 1956, "Over Christmas, Al Newell and I invented a thinking machine",[12] and would write:
[We] invented a computer program capable of thinking non-numerically, and thereby solved the venerable mind-body problem, explaining how system composed of a matter can have the properties of mind.[13]
This statement, that machines can have minds just as people do, would be later named "the Strong AI hypothesis" by philosopher John Searle. It remains a serious subject of debate up to the present day.
[edit] External links
- Newell and Simon's RAND Corporation report on the Logic Theorist
- CMU Libraries: Human and Machine Minds
[edit] Notes
- ^ Crevier 1993, p. 44, although some consider Arthur Samuel's checkers program to be earlier. Christopher Strachey also wrote a checkers program in 1951.
- ^ Crevier 1993, pp. 44-46 and Russell & Norvig 2003, p. 17
- ^ The term "artificial intelligence" was coined by John McCarthy in the proposal for the 1956 Dartmouth Conference. The conference is "generally recognized as the official birthdate of the new science." (Crevier 1993, pp. 49-50)
- ^ Crevier 1993, p. 41-44
- ^ Crevier 1993, p. 44
- ^ Quoted in Crevier 1993, p. 45
- ^ Quoted in Crevier 1993, p. 48
- ^ Quoted in Crevier 1993, p. 49
- ^ Crevier 1993, p. 46
- ^ Crevier 1993, p. 43
- ^ Crevier 1993, p. 46-48
- ^ Quoted on CMU Libraries: Problem Solving Research
- ^ Quoted in Crevier 1993, p. 46
[edit] References
- Crevier, Daniel (1993), AI: The Tumultuous Search for Artificial Intelligence, New York, NY: BasicBooks, ISBN 0-465-02997-3
- Russell, Stuart J. & Norvig, Peter (2003), Artificial Intelligence: A Modern Approach (2nd ed.), Upper Saddle River, NJ: Prentice Hall, ISBN 0-13-790395-2, <http://aima.cs.berkeley.edu/>
