“Colorless green ideas sleep furiously” is a sentence composed by Noam Chomsky in 1957 as an example of a sentence whose grammar (logical form) is correct but whose semantics are nonsensical, and therefore has no meaning to understand. 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.

A poem and an image.

Colourless Green Ideas Sleep Furiously

Behold the pent-up power of the winter tree;
Leafless it stands, in lifeless slumber.
Yet its very resting is revival and renewal:
Inside the dark gnarled world of trunk and roots,
Cradled in the chemistry of cell and sap,
Colourless green ideas sleep furiously
In deep and dedicated doormancy,
Concentrating, conserving, constructing:
Knowing, by some ancient quantum law
Of chlorophyll and sun
That come the sudden surge of spring,
Dreams become reality, and ideas action.
Written by Bryan O. Wright

Colourless Green Ideas Sleep Furiously