Abstract

Philosophers often understand environmental sustainability as a duty of distributive justice between the generations of the earth. Since every generation is equally entitled to the bounty of the natural environment (the thinking goes) every generation should have a fair share of that bounty. But since generations precede each other in time, it is the duty of earlier generations to ensure that later generations receive their fair share. Acting sustainably is the way of meeting this duty, since sustainable practices are those that (ideally) preserve the environment for the future. But what is a ‘fair’ share of something as complex, varied and dynamic as ‘the environment'? How are we to value nature for the purposes of measuring ‘shares’ of it? I think the answer to these questions lies in the difference between sharing something by parts, like a pie, and sharing something by turns, like a bicycle. The generations share the earth by turns, not by parts, and so questions about fairness of shares are questions about turns, not parts. We need to ask what constitutes a ‘fair turn’ with the earth, and for that question we don't necessarily need to be able to commensurate the various parts of nature, just as we don't need to know the relative value of the parts of a bicycle to say what constitutes a fair turn with it.