The theory of the tragedy of the commons is well-known: it is in the interests of any individual to add to his stock of animals on common land, even if that leads to further degradation.

ECONOMIST: Nomadism in Mongolia

In theory, these days are the opportunity for the Commons to exercise its core responsibility to monitor the use of public money - in practice, they're debates on issues raised by select committee reports.

BBC: Week ahead

In theory a petition needs more than 100, 000 signatures to trigger a debate in the House of Commons, which last discussed this emotive subject in the 1990s.

BBC: Conservative MP calls for a referendum on death penalty