<P> 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 . </P> <P> Chomsky writes in his 1957 book Syntactic Structures: </P>

What does the sentence colorless green ideas sleep furiously illustrate