Full Idea
We understand the meaning of a speech act when we know what would make it acceptable.
Gist of Idea
To understand a statement is to know what would make it acceptable
Source
Jürgen Habermas (The Theory of Communicative Action [1981], I:297), quoted by James Gordon Finlayson - Habermas Ch.3:37
Book Reference
Finlayson,James G.: 'Habermas' [OUP 2005], p.37
A Reaction
Finlayson glosses this as requiring the reasons which would justify the speech act.