Full Idea
Once a sentence is understood, an utterance of it may be used to serve almost any extra-linguistic purpose; an instrument that could be put to only one use would lack autonomy of meaning, which means it should not be counted as language.
Gist of Idea
An understood sentence can be used for almost anything; it isn't language if it has only one use
Source
Donald Davidson (Thought and Talk [1975], p.17)
Book Reference
'Mind and Language', ed/tr. Guttenplan,Samuel [OUP 1977], p.17
A Reaction
I find this point very appealing, in opposition to the Wittgenstein view of meaning as use. Passwords seem to me a striking case of the separation of meaning and use. I like the phrase 'autonomy of meaning'. Random sticks can form a word.