In his 1971 book A Theory of Justice, the philosopher John Rawls proposed a way to think about what makes a society's rules genuinely fair, built around a single, deceptively simple thought experiment: imagine designing the basic rules of a society from behind a "veil of ignorance," not knowing in advance what position you personally would occupy within it — rich or poor, talented or not, born into privilege or hardship.
Why not knowing your own position changes the incentives
Rawls's argument was that a person designing society's rules while knowing their own future position would have an obvious incentive to rig the rules in their own favour. Strip away that knowledge — force the designer to reason as if they might end up in any position in the resulting society, including its very worst-off position — and Rawls argued the rational, self-interested choice shifts: a designer genuinely uncertain whether they'll end up rich or destitute has strong reason to build in real protections for the worst-off position, since that position might turn out to be their own.
The difference principle: inequality allowed, but only if it helps the bottom too
From behind the veil, Rawls argued, rational people would agree to two main principles: equal basic liberties for everyone, and what he called the "difference principle" — social and economic inequalities are only justified if they work out to the greatest benefit of the least advantaged members of society. Under this framework, unequal outcomes aren't automatically unfair; a wage gap that incentivises valuable extra effort or specialised training can be justified, but only if the resulting overall system genuinely leaves the worst-off better off than a more equal alternative would, not merely if it makes the already-advantaged better off.
What we're still unsure about
Rawls's framework has drawn serious, sustained challenges from multiple directions since 1971. Libertarian critics, most notably Robert Nozick, argued the difference principle licenses too much redistribution, violating individuals' entitlement to what they've fairly earned regardless of the outcome's overall distribution. Other critics have questioned whether purely self-interested reasoning behind a veil of ignorance would actually produce Rawls's specific two principles, rather than some other arrangement entirely, such as straightforwardly maximising average welfare instead of protecting the worst-off position specifically. More than fifty years on, which set of principles rational people would actually agree to from behind the veil remains a live, unresolved argument in political philosophy, not a settled result Rawls's own reasoning fully closed off.
This sits inside Theories of Justice (Rawls, Nozick, Sen), one of seven topics in Political Philosophy, one of five domains in Philosophy, one of seventeen subjects the app can quiz you on.