Abstract
An analysis is proposed for the common argument that something should be preserved because it is irreplaceable. The argument is shown to depend on modal elements in irreplaceable, existence assumptions of preserve, and the logic of obligation. In terms of this theory it is argued that utilitarianism can account for most, but not all instances of persuasive appeals to irreplaceability. Beingessentially backwards looking, utilitarianism cannot in principle justify preservation of objects irreplaceable because of their history or genesis.