Colorless green ideas sleep furiously.

Ιt's a sentence composed by Noam Chomsky in 1957 as an example of a sentence whose grammar is correct but whose meaning is nonsensical, however some might argue that Chomsky simply wasn't imaginative enough to put the sentence into a context which would give it meaning. It was used to show inadequacy of the then-popular probabilistic models of grammar, and the need for more structured models.

The sentence can be given meaning through polysemy. Both green and colorless have figurative meanings, which still make us able to interpret colorless as "nondescript" and green as "immature" or "environmentally-friendly". So the sentence can be constructed as "nondescript immature ideas have violent nightmares", a phrase not unimaginable in poetry. In particular, the phrase can have legitimate meaning to if green is understood to mean "newly-formed" and sleep can be used to figuratively express mental or verbal dormancy. An equivalent sentence would be "Newly formed bland ideas are unexpressible in an infuriating way." One meaning could be "unimaginative environmentalist ideas are unpopular".

The results have been published of a 1985 literary competition in which the contestants attempted to make Chomsky's sentence meaningful using not more than 100 words of prose or 14 lines of verse.