Cooperative Principle

In semantics, the Cooperative Principle is a principle proposed in Grice (1975), which speakers can be expected to observe in a discourse, as part of a rational and purposeful exchange of information:
 * Make your conversational contribution such as is required, at the stage at which it occurs, by the accepted purpose or direction of the talk exchange in which you are engaged. (Grice 1975: 45).

Examples
A: I am out of petrol.

B: There is a garage around the corner

Under the assumption of cooperativity, B can implicate something about the garage beyond what he only literally says, namely that the garage will provide A with the petrol he needs.

Comment
Grice elaborated this principle in four Maxims (of Quality, Quantity, Relevance and Manner) and used it to explain conversational implicatures.

Links
Utrecht Lexicon of Linguistics

Reference
Grice, H.P. 1975. Logic and conversation. In Syntax and Semantics 3: Speech Acts. Cole, P. & Morgan, J.L. (eds.), 41-58. New York: Academic Press.

Other languages
German Kooperationsprinzip