New Delhi, Sept. 4 -- Impossible. This word, or at least the popular understanding of it, gets a bad rap. Ad slogans dismiss it, while academics wrestle it. Creativity coaches use it as a tool; think of six impossible things before breakfast, they say, just as Alice of Wonderland was advised. Yet, its rap-sheet also exemplifies its value. The word's wonder lies in the fine minds it has wracked.

In academia, an elegant blow was delivered by Amartya Sen to Arrow's 'impossibility theorem'; if there are three options or more, it stated, no voting rule can convert individual preference rankings into a collective rank that satisfies a basic set of must-haves, like Pareto efficiency-nobody can be made better-off without at least one person left...