The basis of this law Plato finds in the fact of the diversity of natures, which fits men for different tasks.158
In this he differs from Adam Smith, who believes that the differences of natural talents in men are much less than is generally supposed. Smith makes the propensity to barter the source of specialization, which, in turn, is based on the interdependence of men. He thus considers the diversities in human nature to be the effect rather than the cause of the division of labor.159
Plato, however, is probably nearer the truth, since the very reason for mutual interdependence is diversity of nature.160
The advantages of specialization, according to Plato,161 are four, as stated above. It enables one to accomplish more work with greater ease, more skilfully, and at the proper season. The second and fourth of these are not mentioned by Adam Smith, but he notes the resulting increase in opulence for all the people, and the development of inventive genius. He also observes that the division of labor causes the growth of capital, and that this in turn increases specialization.162
Of course Plato could not appreciate the important fact of the influence of the division of labor on the development of inventive genius, since he lived before the age of machinery.
Plato is also a forerunner of Adam Smith in his recognition of the fact that the division of labor depends for its advance upon a great increase in the size and complexity of the state.163
It means a multiplication of trades, a development of industry,164 the entrance of the retail trader (κάπηλος),165 and the invention of money as a means of exchange.166