econ 2009 paper1 第22題

contract can be signed / arranged between two parties. Their relationship can be individuals or (consumers and suppliers). For example, some one has excess product over his private use. He makes a contract to other to sell the excess. He has no intention to make a profit even though he may make a profit on the sale. Then, this does not imply the existence of a firm.

Firm is a relationship between consumers and suppliers and to make a profit.