A thought experiment is an imaginary situation designed to bring out our feelings, or what philosophers call ‘intuitions’, on a particular issue. Philosophers use them a lot. Thought experiments allow us to focus more closely on what is at stake. Here the philosophical question is, ‘When is it acceptable to sacrifice one life to save more?’ The story about the runaway carriage allows us to think about this. It isolates the key factors and shows us whether or not we feel that such an action is wrong.
