certain the proportion between two different quantities of labor. The time spent in two different sorts of work will not always alone determine this proportion. The different degrees of hardship endured, and of ingenuity exercised, must likewise be taken into account. There may be more labor in an hour's hard work, than in two hours' easy business; or in an hour's application to a trade which it cost ten years' labor to learn, than in a month's industry, at an ordinary and obvious employment. But it is not easy to find any accurate measure either of hardship or ingenuity. In exchanging indeed the different productions of different sorts of labor for one another, some allowance is commonly made for both. It is adjusted, however, not by any accurate measure, but by the higgling and bargaining of the market, according to that sort of rough equality which, though not exact, is sufficient for carrying on the business of common life.
Every commodity besides is more frequently exchanged for, and thereby compared with, other commodities than with labor. It is more natural, therefore, to estimate its exchangeable value by the quantity of some other commodity than by that of the labor which it can purchase. The greater part of people too understand better what is meant by a quantity of a particular commodity, than by a quantity of labor. The one is a plain palpable object; the other an abstract notion, which, though it can be made sufficiently intelligible, is not altogether so natural and obvious.
But when barter ceases, and money has become the common instrument of commerce, every particular commodity is more frequently exchanged for money than for any other commodity. The butcher seldom carries his beef or his
