Common good

In plain terms

Some goods cannot be divided up and handed out. Clean air, a trusted currency, a functioning legal system, a language, a fishery that is not exhausted. You cannot have your share of these separately from everyone else having theirs.

That creates a structural problem. Each person's interest is to take a little more than their share, since one person's extra use is imperceptible - and if everyone reasons that way, the good disappears for all of them. Nobody intended the outcome and everybody produced it.

The standard answers are the state and the market: regulate it, or divide it into private parcels. What both assume is that people cannot manage it themselves, and the most important empirical work in the area is about how often that assumption is false.

As a philosopher would put it

Aquinas defines law as an ordinance of reason for the common good, made by one with care of the community - which makes the common good a criterion of law rather than one interest among others.

The modern analysis is economic. Public goods are non-excludable and non-rival, which produces free-riding; common-pool resources are rival but hard to exclude anyone from, which produces the tragedy Hardin described in 1968 and used to argue for privatisation or coercion.

Ostrom's work is the decisive correction. Studying irrigation systems, fisheries, forests and pastures, she found many long-enduring institutions in which users governed the resource themselves, and identified design principles common to them: clear boundaries, rules matched to local conditions, participation in rule-making, monitoring by the users, graduated sanctions, cheap conflict resolution and recognition of the right to organise.

Rawls's public reason is the political-liberal version of the same idea - what can be justified to citizens who disagree about the good.

What is actually disputed

Whether the common good is more than an aggregate.

Individualist accounts hold that talk of a good belonging to a community is shorthand for benefits to the individuals composing it, and that anything stronger licenses sacrificing people to an abstraction. Communitarian and Thomist accounts hold that some goods - friendship, a shared culture, mutual trust - are genuinely common, held only together and not divisible into shares, so the reduction loses what is distinctive.

The political stakes are real: appeals to the common good have been used to override individual claims, and the objection is not merely conceptual.

Ostrom's work leaves a different question open. Her design principles describe what has worked at particular scales with identifiable users and repeated interaction. Whether anything analogous is available for a global commons with eight billion users, no boundaries and no monitoring is exactly the problem climate governance has failed to solve.