Pareto efficiency

An arrangement is Pareto efficient when you cannot help anyone without hurting someone else. It is a low bar that turns out to be very demanding.

Pareto efficiency is a state in which no one can be made better off without making at least one other person worse off. Named after Vilfredo Pareto, it is the economist's basic benchmark for whether an allocation of resources wastes any potential gains.

A minimal idea of efficiency

The appeal of the criterion is that it asks for very little agreement. It does not require comparing one person's gain against another's loss, which is contentious; it only asks whether anyone could be helped at no cost to others. If they could, the situation is inefficient, because a free improvement is going unmade. If they could not, it is Pareto efficient: all the costless gains have been exhausted.

Efficient is not the same as fair

The crucial limit is that Pareto efficiency says nothing about fairness. An allocation in which one person has everything and everyone else has nothing can be perfectly Pareto efficient, because taking from the rich to help the poor makes the rich worse off. So efficiency in this sense is necessary for a good outcome but nowhere near sufficient; a society can be efficient and grotesquely unjust at once. Confusing the two is one of the commonest abuses of the idea.

Why it still matters

Despite its silence on fairness, Pareto efficiency is useful precisely because it is uncontroversial as far as it goes. A Pareto improvement, making someone better off and no one worse, is something almost everyone can endorse, which makes it a powerful argument for removing pure waste, deadweight losses, blocked trades, needless inefficiencies, before the harder fights over distribution begin.

Pareto efficiency marks the line between waste and the genuinely hard choices. Reaching it eliminates the improvements no one need object to; beyond it lie the trade-offs between people that economics can describe but not, by this criterion alone, resolve.