Source: Computer Science as Empirical Inquiry: Symbols and Search (1975), p. 120.
“The Physical Symbol System Hypothesis. A physical symbol system has the necessary and sufficient means for general intelligent action.”
Source: Computer Science as Empirical Inquiry: Symbols and Search (1975), p. 116. This is also called the Church–Turing thesis.
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Allen Newell 7
American cognitive scientist 1927–1992Related quotes

Science and the Unseen World (1929)
Context: If to-day you ask a physicist what he has finally made out the æther or the electron to be, the answer will not be a description in terms of billiard balls or fly-wheels or anything concrete; he will point instead to a number of symbols and a set of mathematical equations which they satisfy. What do the symbols stand for? The mysterious reply is given that physics is indifferent to that; it has no means of probing beneath the symbolism. To understand the phenomena of the physical world it is necessary to know the equations which the symbols obey but not the nature of that which is being symbolised.... this newer outlook has modified the challenge from the material to the spiritual world.<!--III, p.30

“Reality must be expressed by a physical symbol.”
Bahai lecture, New York, October 30, 1951; as quoted in Abstract Expressionist Painting in America, W.C, Seitz, Cambridge Massachusetts, 1983, p. 10
1950's

“The observing mind is not a physical system, it cannot interact with any physical system.”
Nature and the Greeks (1954)
Context: The observing mind is not a physical system, it cannot interact with any physical system. And it might be better to reserve the term "subject" for the observing mind. … For the subject, if anything, is the thing that senses and thinks. Sensations and thoughts do not belong to the "world of energy."

Michael Halliday (2005, p. 68) as cited in: Andrew Halliday and Marion Glaser (2011) "A Management Perspective on Social Ecological Systems". In: Human Ecology Review, Vol. 18, No. 1, 2011.
1970s and later
Source: Textual politics: Discourse and social dynamics, 1995, p. 6
Thus It Is, 1989, p. 6
As of a Trumpet, On Eagle's Wings, Thus It Is
Source: Textual politics: Discourse and social dynamics, 1995, p. 159