When we talk of any particular sum of money, we sometimes mean nothing but the metal pieces of which it is composed, and sometimes we include in our meaning some obscure reference to the goods which can be had in exchange for it, or to the power of purchasing which the possession of it conveys. Thus, when we say that the circulating money of England has been computed at eighteen millions, we mean only to express the amount of the metal pieces, which some writers have computed, or rather have supposed, to circulate in that country. But when we say that a man is worth fifty or a hundred pounds a-year, we mean commonly to express, not only the amount of the metal pieces which are annually paid to him, but the value of the goods which he can annually purchase or consume; we mean commonly to ascertain what is or ought to be his way of living, or the quantity and quality of the necessaries and conveniencies of life in which he can with propriety indulge himself. When, by any particular sum of money, we mean not only to express the amount of the metal pieces of which it is composed, but to include in its signification some obscure reference to the goods which can be had in exchange for them, the wealth or revenue which it in this case denotes, is equal only to one of the two values which are thus intimated somewhat ambiguously by the same word, and to the latter more properly than to the former, to the money’s worth more properly than to the money. Thus, if a guinea be the weekly pension of a particular person, he can in the course of the week purchase with it a certain quantity of subsistence, conveniencies, and amusements. In proportion as this quantity is great or small, so are his real riches, his real weekly revenue. His weekly revenue is certainly not equal both to the guinea and to what can be purchased with it, but only to one or other of those two equal values, and to the latter more properly than to the former, to the guinea’s worth rather than to the guinea. If the pension of such a person was paid to him, not in gold, but in a weekly bill for a guinea, his revenue surely would not so properly consist in the piece of paper, as in what he could get for it. A guinea may be considered as a bill for a certain quantity of necessaries and conveniencies upon all the tradesmen in the neighbourhood. The revenue of the person to whom it is paid, does not so properly consist in the piece of gold, as in what he can get for it, or in what he can exchange it for. If it could be exchanged for nothing, it would, like a bill upon a bankrupt, be of no more value than the most useless piece of paper.