In the 2010 thriller *Unthinkable*, a terrorist claims to have hidden nuclear bombs in three American cities. With millions of lives potentially at stake and time running out, the authorities face a horrifying dilemma: **What are they justified in doing to save millions of lives?** Torture one person to save millions? Harm an innocent person if doing so might prevent a catastrophe? Or refuse — even if sticking to your principles could allow thousands to die? It's an extreme fictional scenario. But the philosophical question at its heart is very real: **Are some things simply wrong, whatever the consequences?** Twenty-five years after the attacks of September 11th 2001, questions like these remain deeply relevant. 9/11 and the wars that followed forced governments and ordinary people to confront difficult questions about terrorism, retaliation, torture, civilian casualties and the moral limits of war. **What actually makes something "terrorism"?** Can violence ever be justified in pursuit of a political cause? Is deliberately killing civilians morally different from launching an attack knowing that civilians will probably die? Should we judge the violence of governments by the same moral standards as the violence of terrorist groups? When does self-defence become revenge? And are we capable of making good moral decisions when we're frightened and angry? Perhaps the hardest question is this: ***If terrorism causes a society to abandon some of its own moral principles, has the terrorist won?*** This month, we'll use the 25th anniversary of 9/11 as the starting point for a much older philosophical debate: **When is violence justified? Are some actions always wrong?** **And when we're afraid, do our moral principles still hold?** As always, there's no structure, no right answers, and no need for philosophical expertise. Just come along, grab a drink, and join the conversation. See you there.

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