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Colorless green ideas sleep furiously


"Colorless green ideas sleep furiously" is a sentence composed by Noam Chomsky in his 1957 book Syntactic Structures as an example of a sentence that is grammatically correct, but semantically nonsensical. The sentence was originally used in his 1955 thesis "Logical Structure of Linguistic Theory" and in his 1956 paper "Three Models for the Description of Language". Although the sentence is grammatically correct, no obvious understandable meaning can be derived from it, and thus it demonstrates the distinction between syntax and semantics. As an example of a category mistake, it was used to show the inadequacy of the then-popular probabilistic models of grammar, and the need for more structured models.

The full passage says:

It is fair to assume that neither sentence (1) nor (2) (nor indeed any part of these sentences) has ever occurred in an English discourse. Hence, in any statistical model for grammaticalness, these sentences will be ruled out on identical grounds as equally "remote" from English. Yet (1), though nonsensical, is grammatical, while (2) is not grammatical.

While the meaninglessness of the sentence is often considered fundamental to Chomsky's point, Chomsky was only relying on the sentences having never been spoken before. Thus, even if one were to prescribe a likely and reasonable meaning to the sentence, the grammaticality of the sentence is concrete despite being the first time a person had ever uttered the statement, or any part thereof in such a combination. This was used then as a counter-example to the idea that the human speech engine was based upon statistical models, such as a Markov chain, or simple statistics of words following others.

The sentence can be partially interpreted through polysemy. Both green and colorless have figurative meanings, which allow colorless to be interpreted as "nondescript" and green as either "immature" or pertaining to environmental consciousness. The sentence can therefore be construed as "nondescript immature ideas have violent nightmares", a phrase with less oblique semantics. In particular, the phrase can have legitimate meaning too, if green is understood to mean "newly formed" and sleep can be used to figuratively express mental or verbal dormancy. "Furiously" remains problematic when applied to the verb "sleep", since "furiously" denotes "angrily", "violently", and "intensely energetically", meanings which are generally incompatible with sleep, dormancy, and unconscious agents typically construed as conscious ones, e.g. animals or humans, which truly "sleep".


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