Write the rules, then be born

Anyone who has shared a cake with a sibling knows a simple rule of fairness: one cuts, the other chooses. Suddenly the cutter takes great care. This question applies the same trick to a whole society. You write the rules without knowing which slice of life you will get. The trick can be gamed. In Hesiod's Theogony, Prometheus divides a sacrificed ox into two portions for Zeus to choose from, hiding the meat inside the unappetizing stomach and dressing the bare bones in glistening fat. Zeus takes the fat, though Hesiod insists he saw through the trick. Thomas Paine, in 1797, proposed a rule against the lottery of birth: since land that once belonged to everyone was now owned by some, every citizen should receive a sum of money at twenty-one as compensation. John Rawls turned the cake into a theory of justice in 1971. Behind what he called a veil of ignorance, he argued, you would guarantee basic liberties to everyone and accept inequalities only when they improve the lot of the worst-off, because you might be among them. John Harsanyi had used a similar thought experiment almost two decades earlier and reached a different answer: someone who could land anywhere would treat every position as equally likely and choose the rules that make the average life best, even if a few lives go badly. Robert Nozick objected to the whole exercise in 1974. Justice, he argued, depends on how people came to hold what they have, not on whether the overall pattern looks fair; if a million fans each freely pay a little to watch one great basketball player, no one has been wronged by his fortune. Which rule would you refuse to leave to luck, knowing you could land anywhere, including at the bottom?