Turing, Alan M., in full ALAN MATHISON TURING (b. June 23, 1912, 
London, Eng.--d. June 7, 1954, Wilmslow, Cheshire), English 
mathematician and logician who pioneered in the field of computer 
theory and who contributed important logical analyses of computer 
processes. 
The son of a British member of the Indian Civil Service, Turing 
studied at Sherborne school and at King's College, Cambridge. Many 
mathematicians in the first decades of the 20th century had attempted 
to eliminate all possible error from mathematics by establishing a 
formal, or purely algorithmic, procedure for establishing truth. The 
mathematician Kurt Gödel threw up an obstacle to this effort with his 
incompleteness theorem; Gödel showed that any useful mathematical 
axiom system is incomplete in the sense that there must exist 
propositions whose truth can never be determined (undecidable 
propositions within the system). Turing was motivated by Gödel's work 
to seek an algorithmic method of determining whether any given 
propositions were undecidable, with the ultimate goal of eliminating 
them from mathematics. Instead, he proved in his seminal paper "On 
Computable Numbers, with an Application to the Entscheidungsproblem 
[Halting Problem]" (1936) that there cannot exist any such universal 
method of determination and, hence, that mathematics will always 
contain undecidable (as opposed to unknown) propositions. 
To illustrate this point, Turing posited a simple device that 
possessed the fundamental properties of a modern computing system: a 
finite program, a large data-storage capacity, and a step-by-step mode 
of mathematical operation. This Turing machine , as it was later 
called, is frequently used as a point of reference in basic 
discussions of automata theory and was also the theoretical basis for 
the digital computers that came into being in the 1940s. Turing's 
work, along with that of Gödel, put to rest the hopes of David Hilbert 
and his school that all mathematical propositions could be expressed 
as a set of axioms and derived theorems. (see also Index: Turing 
machine) 
Turing continued his mathematical studies at Princeton University, 
completing a Ph.D. (1938) under the direction of the American 
mathematician Alonzo Church. He then returned to England and accepted 
a renewed fellowship at King's College. During World War II he served 
with the Government Code and Cypher School, at Bletchley, 
Buckinghamshire, where he played a significant role in breaking the 
German "Enigma" codes. In 1945 he joined the staff of the National 
Physical Laboratory in London to lead the design, construction, and 
use of a large electronic digital computer that was named the 
Automatic Computing Engine (ACE). In 1948 he became deputy director of 
the Computing Laboratory at the University of Manchester, where the 
Manchester Automatic Digital Machine (MADAM, as it was referred to in 
the press), the computer with the largest memory capacity in the world 
at that time, was being built. His efforts in the construction of 
early computers and the development of early programming techniques 
were of prime importance. He also championed the theory that computers 
eventually could be constructed that would be capable of human 
thought, and he proposed a simple test, now known as the Turing test , 
to assess this capability. Turing's papers on the subject are widely 
acknowledged as the foundation of research in artificial intelligence. 
In 1952 Turing published the first part of his theoretical study of 
morphogenesis, the development of pattern and form in living 
organisms. He left his work unfinished, however. He apparently 
committed suicide, probably because of the depressing medical 
treatment that he had been forced to undergo (in lieu of prison) to 
"cure" him of homosexuality. 

Turing test, in artificial intelligence, a test proposed (1950) by the 
English mathematician Alan M. Turing to determine whether a computer 
can be said to "think." 
There are extreme difficulties in devising any objective criterion for 
distinguishing "original" thought from sufficiently sophisticated 
"parroting"; indeed, any evidence for original thought can be denied 
on the grounds that it ultimately was programmed into the computer. 
Turing sought to cut through the long philosophical debate about 
exactly how to define thinking by means of a very practical, albeit 
subjective, test: if a computer acts, reacts, and interacts like a 
sentient being, then call it sentient. To eliminate anthropocentric 
bias, Turing suggested the "imitation game," now known as the Turing 
test: a remote human interrogator, within a fixed time frame, must 
distinguish between a computer and a human subject based on their 
replies to various questions posed by the interrogator. By means of a 
series of such tests, a computer's measure of success at "thinking" 
can then be quantified by its probability of being misidentified as 
the human subject. 
Turing predicted that by the year 2000 a computer "would be able to 
play the imitation game so well that an average interrogator will not 
have more than a 70-percent chance of making the right identification 
(machine or human) after five minutes of questioning." 

Turing machine, hypothetical computing device introduced in 1936 by 
the English mathematician and logician Alan M. Turing . He originally 
conceived the machine as a mathematical tool that could infallibly 
recognize undecidable propositions--i.e., those mathematical 
statements that, within a given formal axiom system, cannot be shown 
to be either true or false. (The mathematician Kurt Gödel had 
demonstrated that such propositions exist in any such system.) Turing 
instead proved that there can never exist any universal algorithmic 
method for determining whether a proposition is undecidable. 
As envisaged by Turing, the machine performs its functions in a 
sequence of discrete steps and assumes only one of a finite list of 
internal states at any given moment. The machine itself consists of an 
infinitely extensible tape, a tape head that is capable of performing 
various operations on the tape, and a modifiable control mechanism in 
the head that can store directions from a finite set of instructions. 
The tape is divided into squares, each of which is either blank or has 
printed on it one of a finite number of symbols. The tape head has the 
ability to move to, read, write, and erase any single square and can 
also change to another internal state between one moment and the next. 
Any such act is determined by the internal state of the machine and 
the condition of the scanned square at a given moment. The output of 
the machine--i.e., the solution to a mathematical query--can be read 
from the system once the machine has stopped. However, in the case of 
Gödel's undecidable propositions, the machine would never stop, and 
this became known as the "halting problem." 
The Turing machine is not a machine in the ordinary sense but rather 
an idealized mathematical model that reduces the logical structure of 
any computing device to its essentials. By extrapolating the essential 
features of information processing, Turing was instrumental in the 
development of the modern digital computer. His model became the basis 
for all subsequent digital computers, which share his basic scheme of 
an input/output device (tape and reader), memory (control mechanism's 
storage), and central processing unit (control mechanism).