 Philippa Foot wrote many articles treating issues in metaethics, moral psychology, and applied ethics, as well as one monograph on moral philosophy.  Throughout her career, she defended the objectivity of morality against various forms of noncognitivism and tangled with issues of moral motivation, notoriously changing her mind about whether moral judgments necessarily provide rational agents with reasons for action. To the wider world, and perhaps especially to undergraduate philosophy students, she is best known for inventing the Trolley Problem, which raises the question of why it seems permissible to steer a trolley aimed at five people toward one person while it seems impermissible to do something such as killing one healthy man to use his organs to save five people who will otherwise die. Foot is also known for contributing to the revival of Aristotelian virtue ethics in contemporary philosophy, though it is less well known that she emphatically disavowed being an adherent of this view as it is currently understood.