The question of when governments should intervene to change our behaviour sits at the heart of political philosophy and bioethics.1 In their recent book, Nudge: improving decisions about health, wealth, and happiness, Richard Thaler and Cass Sunstein argue that public and private organisations can and should intervene more often than they currently do to alter people’s behaviour.2 Their thesis is based on the observation that people often behave in ways that are not in their best long term interests. The remedy, they argue, is to present options in such a way as to increase the likelihood that people will choose what they would, on reflection, most prefer. This approach has attracted much interest and support from politicians including Barack Obama and David Cameron.

Thaler and Sunstein call their general approach “libertarian paternalism”—paternalistic in that governments, for example, play an active role in framing options, but libertarian in the sense that people ultimately remain free to choose. Examples of such approaches in the health context include placing fresh fruit …