"Colorless green ideas sleep furiously" is a sentence composed by Noam Chomsky in 1957 as an example of a sentence whose grammar is correct but whose meaning is nonsensical. An example of a category mistake, it was used to show inadequacy of the then-popular probabilistic models of grammar, and the need for more structured models.
The full passage says:
While the meaninglessness of the sentence is often considered fundamental to Chomsky's point, Chomsky was relying upon this only to ensure that the sentences had never been spoken before. Thus, even if one were to prescribe a likely and reasonable meaning to the sentence, the grammaticalness of the sentences are concrete despite being the first time a person had ever heard that phrase, or those words in such a combination. This is also a counter-example to a challenging idea at the time that the human speech engine was based upon a Markov Chain, and simple statistics of words following others.
- Colorless green ideas sleep furiously.
- Furiously sleep ideas green colorless.
It is fair to assume that neither sentence (1) nor (2) (nor indeed any part of these sentences) had 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.
This statistical model defines a similarity metric, whereby sentences which are more like those within a corpus in certain respects are assigned higher values than sentences less alike. Pereira's model does assign an ungrammatical version of the same sentence a lower probability than the syntactically correct form. However, it is not clear that the model assigns every ungrammatical sentence a lower probability than every grammatical sentence. That is, "colorless green ideas sleep furiously" may still be statistically more "remote" from English than some ungrammatical sentences.
Writers have attempted to provide the sentence meaning through context, the first of which was written by Chinese linguist Yuen Ren Chao. A literary competition was held at Stanford University in 1985, in which the contestants were invited to make Chomsky's sentence meaningful using not more than 100 words of prose or 14 lines of verse. An example entry from the competition, from C.M. Street, is:
The game of cadavre exquis (1925) is a method for generating nonsense sentences. It was named after the first sentence generated, Le cadavre exquis boira le vin nouveau (the exquisite corpse will drink the new wine).
In the popular game of "Mad Libs", a chosen player asks each other player to provide parts of speech without providing any contextual information (e.g., "Give me a proper noun", or "Give me an adjective"), and these words are inserted into pre-composed sentences with a correct grammatical structure, but in which certain words have been omitted. The humor of the game is in the generation of sentences which are grammatical but which are meaningless or have absurd or ambiguous meanings (such as 'loud sharks'). The game also tends to generate humorous double entendres.
There are doubtlessly earlier examples of such sentences, possibly from the philosophy of language literature, but not necessarily uncontroversial ones, given that the focus has been mostly on borderline cases. For example, followers of logical positivism held that "metaphysical" (i.e. not empirically verifiable) statements are simply meaningless; e.g. Rudolph Carnap wrote an article where he quite literally claimed that almost every sentence from Heidegger was grammatically correct, yet meaningless. Of course, some philosophers who were not logical positivists disagreed with this; at the same time, many who had tried to read Heidegger agreed completely.
The philosopher Bertrand Russell used the sentence "Quadruplicity drinks procrastination" to make a similar point; W.V. Quine took issue with him on the grounds that for a sentence to be false is nothing more than for it not to be true; and since quadruplicity doesn't drink anything, the sentence is simply meaningless, not false.
Examples like Tesnière's and Chomsky's are the least controversially nonsensical, and Chomsky's example remains by far the most famous.
Clive James wrote a poem titled "A Line and a Theme from Noam Chomsky" in his book, Other Passports: Poems 1958-1985. It opens with Chomsky's second meaningless sentence and discusses the Vietnam War.
Stephen Fry delivers the following line in an A Bit of Fry and Laurie sketch entitled Language Conversation: "I can say this sentence and be confident it has never been uttered before in the history of human communication: "Hold the newsreader's nose squarely, waiter, or friendly milk will countermand my trousers."" George Carlin used a similar comedy routine called "Things You Never Hear", on his album Parental Advisory: Explicit Lyrics.
Another approach is to create a syntactically-correct, easily parseable sentence using nonsense words; a famous such example is "The gostak distims the doshes". Lewis Carroll's Jabberwocky is also famous for using this technique, although in this case for literary purposes.
Other "meaningless utterances" are ones that make sense, are grammatical, but have no reference to the real world, such as "The present Queen of France rides a unicorn." There is no such person as the present Queen of France, and there are, to current knowledge, no such things as unicorns.