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 important. Agricultural sustainability may be considered in the same way.
The notion that agricultural sustainability should be regarded as a process rather
than as a prescribed set of practices, and that it has a generalised core meaning, may
pose problems when one wishes to assess the sustainability of systems. Pretty (1995)
argues that: ``At the farm or community level, it is possible for actors to weigh up,
trade o and agree on these criteria for measuring trends in sustainability. But as we
move to higher levels. . .to districts, regions and countries, it becomes increasingly
dicult to do this in any meaningful way''