What is public good?
From the standpoint of economics, in order for goods and services to be classified as public goods, they must be both non-rivalrous, and non-excludable.
Goods and services are considered rivalrous if consumption by one party serves to prevent consumption by another party. Goods and services are considered excludable if they are only accessible to paying parties. Public goods, then, are those goods and services that are available to all, where the supply does not decrease to one party through consumption by another party.
In his landmark 1954 paper, The Pure Theory of Public Expenditure, Paul Samuelson defined collective consumption of good and services as “[goods] which all enjoy in common in the sense that each individual's consumption of such a good leads to no subtractions from any other individual's consumption of that good.”
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