Adam Smith (Excerpts)
It is not because wealth consists more essentially in money than in goods, that the merchant finds it generally more easy to buy goods with money, than to buy money with goods; but because money is the known and established instrument of commerce, for which every thing is readily given in exchange, but which is not always with equal readiness to be got in exchange for everything. The greater part of goods besides are more perishable than money, and he may frequently sustain a much greater loss by keeping them. When his goods are upon hand too, he is more liable to such demands for money as he may not be able to answer, than when he has got their price in his coffers. Over and above all this, his profit arises more directly from selling than from buying. and he is upon all these accounts generally much more anxious to exchange his goods for money, than his money for goods. But though a particular merchant, with abundance of goods in his warehouse, may sometimes be ruined by not being able to sell them in time, a nation or country is not liable to the same accident. The whole capital of a merchant frequently consists in perishable goods destined for purchasing money. But it is but a very small part of the annual produce of the land and labour of a country which can ever be destined for purchasing gold and silver from their neighbours. The far greater part is circulated and consumed among themselves; and even of the surplus which is sent abroad, the greater part is generally destined for the purchase of other foreign goods. Though gold and silver, therefore, could not be had in exchange for the goods destined to purchase them, the nation would not be ruined. It might, indeed, suffer some loss and inconveniency, and be forced upon some of those expedients which are necessary for supplying the place of money. The annual produce of its land and labour, however, would be the same, or very nearly the same, as usual, because the same, or very nearly the same consumable capital would be employed in maintaining it. And though goods do not always draw money so readily as money draws goods, in the long-run they draw it more necessarily than even it draws them. Goods can serve many other purposes besides purchasing money, but money can serve no other purpose besides purchasing goods. Money, therefore, necessarily runs after goods, but goods do not always or necessarily run after money. The man who buys, does not always mean to sell again, but frequently to use or to consume; whereas he who sells, always means to buy again. The one may frequently have done the whole, but the other can never have done more than the one-half of his business. It is not for its own sake that men desire money, but for the sake of what they can purchase with it.
From Adam Smith, An Inquiry Into the Nature and Causes of the Wealth of Nations, Edwin Cannan, ed.