The Greeks had no specific word for production, as we have, since industry, though well developed, was not a dominant feature of Greek life, and economics had not become a separate science. The word ἐργασία, meaning “labor” or “business,” served the purpose. The term was used of productive labor,[395] of building or manufacturing,[396] of work in raw materials,[397] most commonly of agriculture,[398] of industries in general,[399] of the trades, commerce, or other business for money-making,[400] and of a guild of laborers.[401] The term ἡ ποιητικὴ τέχνη, “the productive art,” which approaches more nearly to a specific, technical expression, was also used.[402] Thus, though there is no clear-cut term for production, the statement of Zimmern[403] that the Greeks had no better word for “business” than ἀσχολία, “lack of leisure,” is hardly warranted. Xenophon was far more interested than Plato or Aristotle in the problem of practical production. His shrewd discussion of agriculture, and his urgent appeal to Athens to increase her revenues by systematic exploitation of the mines, and by the encouragement of industry and commerce, reveal a mind awake to economic advantage. Though at times he seems almost to make war and agriculture the only true means of production, it is evident that he has a live interest in all means of acquisition.[404] Toward the theory of production, however, his contribution is not large. In the _Economics_, he recognizes the importance of labor and natural resources in production, and in the _Revenues_, he sees the necessity of capital.[405] But naturally, like Aristotle and the southern planter, he confuses capital with labor, in the person of the slave.[406] The fable of the dog and the sheep reveals a knowledge of the machinery of production, and some insight into the proper relation between the employer and the laborer.[407] Xenophon’s distinct contribution to future economic thought, however, consists in his appreciation of the fact that economic production has its definite limits; that the same ratio of profits cannot be increased indefinitely by the constant addition of more labor and capital, but that these must be proportioned to the greatest possible return.[408] To be sure, he does not appreciate the scientific significance of the principle. His purpose is rather to emphasize the danger of overproduction, and he even fails to grasp the necessary application of this danger to the silver mines. However, as the enunciator of the principle, he may be called the forerunner of the doctrine of diminishing returns.