The Wealth of Nations by Part 2 Chapter 2 Page 13

of the money, of which not a single farthing can ever make any part of either.

It is the ambiguity of language only which can make this proposition appear either doubtful or paradoxical. When properly explained and understood, it is almost self-evident.

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.