Terms of Trade and Voluntary Exchange
Specialization creates potential output gains, but whether both sides trade depends on the terms of trade: how much of one good exchanges for a unit of another.
Find the mutually acceptable interval
Lin's opportunity cost of one sandwich is 3 coffees, while Zhou's is 4. If Lin exports sandwiches and Zhou exports coffee, the price per sandwich must satisfy:
At 3.5 coffees per sandwich, Lin receives more coffee than the 3 that self-production would yield, while Zhou pays less than the 4 coffees forgone by making a sandwich personally. Both save opportunity cost.
Set a trading price
Lin's sandwich costs 3 coffees; Zhou's costs 4. Choose coffees paid per sandwich.
3.5 — Strict gains for both sides.
Endpoints need careful interpretation. When the price exactly equals one side's opportunity cost, that side is normally indifferent and receives no strict gain. Transport, bargaining, and payment costs narrow the workable interval.
Voluntary does not mean equally fair
Voluntary trade means both sides expect to improve relative to their available alternatives; otherwise they can refuse. It does not prove that gains are equal or that initial resources, information, and bargaining power are fair. A price closer to one party's opportunity cost normally gives more of the trade surplus to the other party.
Economic analysis should separate two questions: does exchange create total gains, and how are those gains distributed? Information asymmetry, market power, and external effects may alter the answer.
KNOWLEDGE QUIZ
Find a mutually beneficial trade range
A gives up 2 sacks of rice per kilogram of honey; B gives up 5. A exports honey. State the beneficial terms of trade and analyze a price of 3 sacks per kilogram.