In early life, the philosopher, theologian and scientist Robert Boyle (1627–1691) wrote extensively on moral matters. One of the extant early documents written in Boyle's hand deals with the morality of our treatment of non-human animals. In this piece (probably written about 1647) Boyle offered a number of arguments for extending moral concern to non-human animals. Since the later Boyle routinely vivisected or otherwise killed animals in his scientific experiments, we are left with the biographical questions, did his views change, and if so, why? as well as with the philosophical questions, what were his arguments and how good are they?