The efficiency of language is a property that is viewed by Barwise and Perry (1983) as being essential to theories of semantics. Language is efficient in the sense that exactly the same sentence can be used over and over again. While the words of the sentence have the same meaning, the interpretation of the sentence will vary from use to use, depending upon the situation. In one famous example from their book, Barwise can say to Perry "I am right, you are wrong" which has a very different interpretation when Perry says to Barwise "I am right, you are wrong" even though the sentence being used is identical both times.
Accounting for the efficiency of language was argued by Barwise and Perry to require considering the situations in which sentences were uttered; their theory can be viewed as an example of transporting Gibson's (1979) theory of ecological perception into the realm of language and semantics.