Definition
The veil of ignorance is a thought experiment which says the fairest rules are the ones you'd pick without knowing who you will be born as. American philosopher John Rawls proposed it. Picture a imaginary curtain that hides your wealth, gender, talents, and physical condition. Design society's institutions from behind it, and you'll build a just society that looks out even for its most vulnerable members.
What if you get the last slice?
What's the easiest way to split a cake fairly? Let the person who cuts it take the last piece. Since the cutter doesn't know which slice they'll end up with, they try their very best to make every slice the same size. If one slice is even a little smaller, it might be theirs.
The veil of ignorance stretches this cake-cutting rule across a whole society. It's a philosophical thought experiment. The 'veil' is a thin curtain that covers your face. Before anyone decides a society's laws and rules, imagine that everyone puts on this veil and completely forgets everything about their own situation.
Someone behind the veil has no idea whether they'll be born rich or poor, with great talents or a physical disability. If you might be born into the worst position in the world, what rules would you choose? Rawls believed people would agree on rules that make the situation of the worst-off person as good as it can possibly be. Still, some thinkers disagree. The economist John Harsanyi, for one, argued that people behind the veil would instead choose the rules that maximize the average happiness of society as a whole.
A bit more precisely: Rawls's two principles
To be more precise, Rawls believed that behind the veil, people would agree on two core principles. The first is that everyone should enjoy the same basic liberties, such as freedom of speech and the right to vote.
The second principle has two parts. First, jobs and opportunities must be open to everyone on fair terms (fair equality of opportunity). On top of that, social and economic inequalities, like differences in income, wealth, or status, are acceptable only if they bring the greatest benefit to the people who are worst off in society. This is called the 'difference principle.' Rawls put the first principle, basic liberty, ahead of this one.
Splitting everything equally isn't the only version of justice. Say we pay inventors and engineers more so they develop innovative technology, and thanks to that, even the most left-out neighbors can ride affordable public transit. That kind of inequality can count as socially beneficial.
Why does it matter in the real world?
In real life, none of us wears the veil. So it's natural to see the world only from where we stand and to push for rules that favor us. People who already own a home hope home prices rise. People who climb stairs with ease rarely notice how hard a building without a ramp can be.
But trying on the veil when you design a new policy or system is surprisingly powerful. It makes you switch places in your mind: 'If I used a wheelchair, could I use this bus stop easily?' 'If I were a young person with no connections, standing on my own, would this system feel fair?'
So the veil of ignorance works as a thinking tool. You set your own situation aside for a moment and ask what a fair starting line that everyone could accept would look like. That said, people still disagree about which rules this experiment produces, and whether those rules are truly just.
Common misconceptions
The veil of ignorance argues for simple, mechanical equality, where everyone must share exactly the same wealth.
John Rawls did not oppose inequality outright. He thought inequality is justified if it helps improve the situation of the people who are worst off. But the reason isn't 'they worked hard, so they deserve more.' It's that the inequality benefits the least advantaged.
Where you meet it
Adding low-floor buses and elevators to public transit can be explained through the veil of ignorance: anyone could end up with limited mobility.
When kids split a pizza, letting the one who cuts it pick last makes them work hard to cut the slices as evenly as possible.
In one sentence
Rawls argued that the fairest society comes from setting rules as if you could turn out to be the most disadvantaged person in it.