Tom Sutcliffe discusses how we make decisions with the Nobel prize-winning psychologist Daniel Kahneman. Moral choices in politics can be a complicated business, according to the academic and former politician Michael Ignatieff, who explores whether the age of international intervention is over. Doctors work under the oath 'do no harm', but the neurosurgeon Henry Marsh says the decision whether to operate on a brain is rarely that simple. High emotion can cloud your judgement and the writer Lisa Appignanesi looks back at sensational crimes of passion to ask how far the perpetrators were responsible for their actions.

Producer: Katy Hickman.