Obituary: Philippa Foot, Philosopher

Philippa Foot, a philosopher, argued that moral judgments have a rational basis, and who introduced the renowned ethical thought experiment known as the Trolley Problem. In her early work, notably in the essays Moral Beliefs and Moral Arguments published in the late 1950s, Foot took issue with philosophers such as RM Hare and Charles Stevenson, who maintained that moral statements were ultimately expressions of attitude or emotion because they could not be judged true or false in the same way factual statements could be.

Foot countered this "private-enterprise theory," as she called it, by arguing the interconnectedness of facts and moral interpretations. Further, she insisted that virtues such as courage, wisdom and temperance are indispensable to human life and the foundation stones of morality. Her writing on the subject helped establish virtue ethics as a leading approach to the study of moral problems.

"She's going to be remembered not for a particular view or position, but for changing the way people think about topics," said Lawrence Solum, who teaches the philosophy of law at the University of Illinois and studied under Foot. "She made the moves that made people see things in a fundamentally new way. Very few people do that in philosophy."

It was the Trolley Problem, however, that captured the imagination of scholars outside her discipline. In 1967, in the essay The Problem of Abortion and the Doctrine of the Double Effect, she discussed the moral distinctions between intended and unintended consequences, between doing and allowing, and between positive and negative duties - the duty not to inflict harm weighed against the duty to render aid. The most arresting of her examples was the ethical dilemma faced by the driver of a runaway trolley hurtling toward five track workers. By diverting the trolley to a spur where just one worker is on the track, the driver can save five lives.

But what about a surgeon who could also save five lives - by killing a patient and distributing the patient's organs to five other patients who would otherwise die? By means of such problems, Foot hoped to clarify thinking about the moral issues surrounding abortion in particular, but she applied a similar approach to matters such as euthanasia.

The philosopher Judith Jarvis Thomson added two complications to the Trolley Problem that are now inseparable from it. Imagine, she wrote, a bystander who sees the trolley racing toward the track workers and can divert it by throwing a switch along the tracks.Unlike the driver, who must choose to kill one person or five, the bystander can refuse to intervene or, by throwing the switch, accept the unintended consequence of killing a human being, a choice endorsed by most people presented with the problem.

Or suppose, she suggested, that the bystander observes the impending trolley disaster from a footbridge over the tracks and realises that by throwing a heavy weight in front of the trolley he can stop it. As it happens, the only available weight is a fat man standing next to him. Most respondents presented with the problem saw a moral distinction between throwing the switch and throwing the man on to the tracks, even though the end result, in lives saved, was identical.

Philippa Judith Bosanquet was born on 3 October, 1920, in Owston Ferry, Lincolnshire, and grew up in Kirkleatham, in North Yorkshire. Her mother Edith was a daughter of the US president Grover Cleveland. Her father, William, was a captain in the Coldstream Guards when he married and later took over the running of a large Yorkshire steel works. Foot studied philosophy, politics and economics at Somerville College, Oxford, where she earned a bachelor's degree in 1942.

During the Second World War, she worked as a researcher at the Royal Institute of International Affairs, sharing a London flat with the future novelist Iris Murdoch. In 1945 she married the historian MRD. Foot, after Murdoch left him for the economist Thomas Balogh. The marriage ended in divorce.

Foot began lecturing on philosophy at Somerville in 1947, a year after receiving her master's degree, and rose to the positions of vice-principal and senior research fellow before retiring in 1988. In 1974 she became a professor of philosophy at the University of California, Los Angeles, from which she retired in 1991.

In the 1970s, Foot revisited some of her assertions about the objective nature of morality, allowing a measure of subjectivism to creep into her discussions of topics such as abortion and euthanasia.

In Natural Goodness (2001), she offered a new theory of practical reason, arguing that morals are rooted in objective human needs that can be compared to the physical needs of plants and animals and described using the same words. "We describe defects in human beings in the same way as we do defects in plants and animals," she later said. "I once began a lecture by saying that in moral philosophy, it's very important to begin by talking about plants."

Despite her influence, Foot remained disarmingly modest, saying: "I have a certain insight into philosophy, I think. But I'm not clever, I don't find complicated arguments easy to follow."