If you want people to do the right thing, make it easy.” That is the simplest possible summary of Nudge by Cass Sunstein and Richard Thaler. We are all fallible creatures, and so benevolent policymakers need to make sure that the path of least resistance goes to a happy destination. It is a simple but important idea, and deservedly influential: Mr Sunstein became a senior adviser to President Obama, while Mr Thaler is this year’s winner of the Nobel memorial prize in economics.

Policy wonks have nudged people to sign up for organ donation, to increase their pension contributions — and even insulate their homes by coupling home insulation with an attic-decluttering service. All we have to do is make it easy for people to do the right thing.

But what if you want people to do the wrong thing? The answer: make that easy; or make the right thing difficult. Messrs Thaler and Sunstein are well aware of the risk of malign nudges, and have been searching for the right word to describe them. Mr Thaler likes “sludge” — obfuscatory language or procedures that accidentally or deliberately encourage inertia. Voter ID laws, he says, are a good example of sludge, calculated to softly disenfranchise. Meanwhile Mr Sunstein has written an entire book about the “ethics of influence”.