Pareto efficiency
Pareto efficiency, also known as Pareto optimality, is an economic state in which resources are allocated such that it is impossible to reallocate them to make any one agent better off without making at least one other agent worse off.[1] The concept originates from the work of Italian economist and sociologist Vilfredo Pareto (1848–1923), who formalized it in his Manual of Political Economy (1906), describing an "ophelimity" maximum where no variation in the economic system can increase the ophelimity (satisfaction or utility) of one residue class without decreasing that of another.[2][3] In welfare economics, Pareto efficiency serves as a benchmark for evaluating resource allocations, underpinning key results such as the first fundamental theorem of welfare economics, which asserts that a competitive market equilibrium is Pareto efficient under assumptions of perfect information, no externalities, and complete markets.[4] This theorem highlights how decentralized market processes can achieve efficiency without central planning, provided those ideal conditions hold.[4] The second fundamental theorem complements this by showing that any Pareto efficient allocation can be supported as a competitive equilibrium through appropriate initial endowments or lump-sum transfers, emphasizing the separation of efficiency from equity concerns.[4] Despite its analytical utility, Pareto efficiency has notable limitations: it identifies a set of efficient outcomes but remains silent on distributive justice, permitting allocations that are efficient yet starkly unequal, such as one where a single agent consumes all resources.[5] Real-world deviations from the theorem's assumptions—such as market failures via externalities, public goods, or imperfect competition—often prevent markets from attaining Pareto efficiency, necessitating policy interventions that must balance efficiency gains against potential efficiency losses.[5] These characteristics define Pareto efficiency as a positive tool for assessing allocative efficiency rather than a prescriptive criterion for social optimality.[6]