And this leads to a vital distinction, which quantity theorists almost always lose: the distinction between the volume of _production_, and the volume of _trade_. Even in the mechanical system of causation which they describe, it is true only of production and transportation that _technical_ and _physical_[243] factors are of primary significance, and that money is of minor significance. For trade and commerce, money is always highly important. To the extent that a region is primarily given over to the primary productive activities, mining, and agriculture, such trading as is necessary can be done by means of a small amount of money, supplemented by barter and long-time book-credit. A region or a city whose chief business is _commerce_, however, needs a large part of its capital in the form of money, and of banking capital, which is largely invested in money for banking reserves. _Trade_, as distinguished from industry (and it is after all trade that is under discussion), is helped or hindered as its tools are more or less abundant. These considerations would suggest that the elasticity of the demand for the use of money is greater than the elasticity of demand for the use of capital in almost any other form. Production is, indeed, limited by labor supply and natural resources, in considerable degree. _Trade_,[244] however, even from the standpoint of mechanical causation, is limited chiefly by the relation between the profits to be made in commercial transactions, and the "price" that must be paid for the money and credit that are required to put them through. There are enormous numbers of transfers that could be made to advantage if there were no cost at all involved. They are not made, because exchanging requires pecuniary capital. Let the pecuniary capital increase, however, and sub-marginal exchanges become worth while, the general margin is lowered. Commerce is the most highly flexible and elastic portion of the whole productive process. The elasticity of demand for commercial capital is, thus, greater than the elasticity of demand for any other form of capital.