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 well-formed, but semantically nonsensical. The sentence was originally used in his 1955 thesis The Logical Structure of Linguistic Theory and in his 1956 paper "Three Models for the Description of Language". There is no obvious understandable meaning that can be derived from it, which demonstrates the distinction between syntax and semantics, and the idea that a syntactically well-formed sentence is not guaranteed to be semantically well-formed as well. As an example of a category mistake, it was used to show the inadequacy of certain probabilistic models of grammar, and the need for more structured models. Senseless but grammatical Chomsky writes in his 1957 book Syntactic Structures: 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 that accounts for grammaticality, 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. Colorless green ideas – which functions as the subject of the sentence – is an anomalous string for at least two reasons: The adjective colorless can be understood as dull, uninteresting, or lacking in color, and so when it combines with the adjective green, this is nonsensical: an object cannot simultaneously lack color and have the color of green. In the phrase, colorless green ideas the abstract noun idea is described as being colorless and green. However, due to its abstract nature, an idea cannot have or lack color. Sleep furiously – which functions as the predicate of the sentence – is structurally well-formed; in other words, it is grammatical. However the meaning that it expresses is peculiar, as the activity of sleeping is not generally taken to be something that can be done in a furious fashion. Nevertheless, sleep furiously is both grammatical and interpretable, though its interpretation is unusual. When Colorless green ideas combines with sleep furiously, this creates a sentence which is felt to be nonsensical by some. On the one hand, an abstract noun like idea is taken to not have the ability to engage in an activity like sleeping. On the other hand, some think that it is possible for an idea to