The Wealth of Nations by Part 2 Chapter 2 Page 17

taken together, must always be great or small in proportion to the quantity of consumable goods which they can all of them purchase with this money. The whole revenue of all of them taken together is evidently not equal to both the money and the consumable goods; but only to one or other of those two values, and to the latter more properly than to the former.

Though we frequently, therefore, express a person’s revenue by the metal pieces which are annually paid to him, it is because the amount of those pieces regulates the extent of his power of purchasing, or the value of the goods which he can annually afford to consume. We still consider his revenue as consisting in this power of purchasing or consuming, and not in the pieces which convey it.

But if this is sufficiently evident