liar paradox

Paradox derived from the statement attributed to the Cretan prophet Epimenides (6th century BC) that all Cretans are liars. If Epimenides' statement is taken to imply that all statements made by Cretans are false, then since Epimenides was a Cretan, his statement is false (i.e., not all Cretans are liars). The paradox's simplest form arises from considering the sentence “This sentence is false.” If it is true, then it is false, and if it is false, then it is true. Consideration of such semantic paradoxes led logicians to distinguish between object language and metalanguage and to conclude that no language can consistently contain a complete semantic theory for its own sentences.

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"Liar!" is a science fiction short story by Isaac Asimov that first appeared in the May 1941 issue of Astounding Science Fiction and was reprinted in the collections I, Robot (1950) and The Complete Robot (1982). It was Asimov's third published positronic robot story.

According to the Oxford English Dictionary, this story was the origin of the word "robotics".

In 1969 this short story was adapted into an episode of the British television series Out of the Unknown, although only a few short clips of this episode are known to exist.

Plot summary

Through a fault in manufacturing, a robot, HRB-34 (Herbie) is created that has the ability to read minds. While the roboticists at U.S. Robots and Mechanical Men are trying to analyze what happened and why, the robot tells them what other people are thinking. But the First Law still applies to this robot, and so it deliberately lies when necessary to avoid hurting their feelings, especially in terms of the problem it was initially designed to solve. However, by lying, it is hurting them anyway. When it is confronted with this fact by Susan Calvin (to whom it told a lie that was particularly painful to her when it was shown to be false), the robot experiences an irresolvable logical conflict, which results in a total mental breakdown.

Major themes

The application of the Three Laws of Robotics is again the subject here, like in many others of Asimov's stories, but in terms of telepathy. The lexical ambiguity that is explored here is the definition of injury, the robot having to take into account psychological injury as well as physical.

The story is also a striking early example of the "Does not compute" theme: an artificial intelligence being unable to resolve cognitive dissonance and hence self-destructing.

Another telepathic robot called R. Giskard Reventlov was later introduced by Asimov in the novel The Robots of Dawn, which takes place so long after "Liar!" that the events of "Liar!" are considered mythical.

"Liar!" also shows one of the first computers in science fiction not to always tell the truth, a paradigm kept by other writers for quite a while.

See also

• Liar paradox
• Does not compute
• HAL 9000, who confronted a similar paradox when told to keep a secret, while being "hardwired" to return information truthfully and without concealment.