This raises the possibility of sustainability being considered so vague a concept
that it has little meaning and should be discarded. This issue is considered in a more
general form by Jacobs (1995). Noting that there are at least 386 de®nitions of sus-
tainable development, and that both Mrs. Thatcher and Friends of the Earth have
signed up to it, he asks if it is meaningless. Jacobs answers `no' because: ``. . .this is to
mistake what it means for a political principle to be meaningful. There are far more
than 386 de®nitions of democracy, but that doesn't mean the concept is meaningless.
Nor does the fact that dierent people disagree on what counts as democracy. Key
political principles like democracy. . .are contestable-they are open to dierent
interpretations- but they carry a core meaning. . .which is substantive and impor-
tant.'' (p. 9). Agricultural sustainability may be considered in the same way.