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