Full Idea
If a runaway tram is heading towards a track on which five people are standing, and there is someone who can switch the points, diverting it onto a track where there is one person,...this is diverting a fatal sequence, not starting a new one.
Gist of Idea
Making a runaway tram kill one person instead of five is diverting a fatal sequence, not initiating one
Source
Philippa Foot (Killing and Letting Die [1985], p.85)
Book Reference
Foot,Philippa: 'Moral Dilemmas' [OUP 2002], p.85
A Reaction
Suppose the one person was of immense community value, or someone you personally hated? Clearly she is interested in the agent's virtue, rather than the actual consequences.