A runaway train, five workers, one lever: the trolley problem is debated everywhere from internet forums to self-driving car boardrooms. This episode goes beyond the puzzle to the woman who co-created it, Philippa Foot, and argues that she rescued modern morality from being dismissed as meaningless emotion. Born Philippa Bosanquet in 1920 in Lincolnshire, the granddaughter of US President Grover Cleveland, she began studying PPE at Somerville College, Oxford, in 1939 before leaving to serve as a government economist from 1942 to 1947, a wartime experience of rationing and life-or-death trade-offs that shaped her demand for a practical philosophy.

Back at Oxford she shared an apartment with Iris Murdoch and forged a combative intellectual partnership with G.E.M. Anscombe, who connected her to Wittgenstein's focus on how language is actually  ...