The Greek philosopher, Plato, who looked down on commerce as a debasing occupation nevertheless considered it necessary. As he illustrated, people have many needs; no one is self-sufficient. Since people have many wants and many persons are needed to supply them, it becomes necessary for one to take a helper for one purpose, and another helper for another purpose, and so on.
The first and greatest need of man is food. The second is shelter, and the third is clothing and the like. How can the State address all these needs?
Plato explains: Let us say that one person is a husbandman, another person is a builder, another a weaver, and another a shoemaker. Would the husbandman work four times as long and as much to produce the needs of the four of them? Or would each of them produce only for himself—his food, his house, his clothes, apportioning his time to produce each of his own needs?
People are not all alike. There are differences in their skills adapted to different occupations. It is better for each person to specialize in his own skill than to perform different occupations. First of all, a work is better done when the worker has only one occupation than when he has many. Further, a person's business cannot afford to wait for a worker who works on a job only at his pleasure. The worker must follow up what he is doing and make his occupation his primary concern. Finally, all things are produced more plentifully, easily, and of a better quality when the worker works on one job in which he is skillful, and leaves other things not within his specialization.
Consequently, more workers of other skills will be needed. For example, a farmer will attend to farming and not to the production of his farming implements. A builder will attend to the construction of a house and not to the manufacturing of his tools; and so with the weaver and the shoemaker. Workers in the other skills will share their occupation and thus contribute to the growth of the State.
It is also necessary that each city produce more than it requires for its own needs, in order to provide for the needs of other cities. Then there will be a need for more producers in each city, and there will likewise be a need for importers and exporters. If goods are to be carried across the sea, there will be a need for skillful sailors in considerable number. A market will naturally emerge, together with the use of money, as token for purposes of exchange.
Within the domestic market, it is possible that some producers may bring their products at times when there are no buyers. They will not just sit idly in the market place. They will look for people who would undertake the task of salesmen. Their duty is to be in the market, to give money in exchange for goods to those who desire to sell, and to take money from those who desire to buy. They sit in the market place engaged in buying and selling. They constitute the class of retailers; while those who wander from one city to another are called merchants.