In his book, Chance and Necessity (1972), the distinguished biochemist Jacques Monod sets out to determine the distinctiveness of living things by means of a contrast with that other class of things – apparently also endowed with properties of form and function – commonly known as artefacts. Monod invites us to imagine ourselves as the intelligent inhabitants of another planet, who are concerned to find out whether there is any evidence of artefactproducing activity back on Earth. We plan to send a spacecraft to Earth, equipped with a computer programmed to distinguish, on the basis of a range of input data, between objects that are artefacts and objects that are not. How should this program be written?