He gets out of the difficulty by making commensurable through money what is in itself incommensurable, so far as it is necessary for practical purposes. “Τῇ μὲν οὔν ἀληθείᾳ ἀδύνατον τὰ τοσοῦτον διαφέροντα σύμμετρα γενέσθαι, πρὸς δὲ τὴν χρείαν ἐνδέχεται ἰκανῶς.” (“In truth it is impossible to make things that are so different, commensurable, but for practical purposes it is permissible.”) Aristotle, Ethica Nicomachea. l. 5, c. 8, edit. Bekkeri. Oxonii, 1837.
The peculiar circumstance that, while the ounce of gold serves in England as the unit of the standard of money, it is not divided into aliquot parts has been explained as follows: “Our coinage was originally adapted to the employment of silver only—hence an ounce of silver can always be divided into a certain adequate number of pieces of coin; but as gold was introduced at a later period into a coinage adapted only to silver, an ounce of gold cannot be coined into an adequate number of pieces.” Maclaren: “A Sketch of the History of the Currency,” p. 16, London, 1858.
“Money may continually vary in value and yet be as good a measure of value as if it remained perfectly stationary. Suppose, for instance, it is reduced in value.... Before the reduction, a guinea would purchase three bushels of wheat or 6 days’ labour; subsequently it would purchase only 2 bushels of wheat, or 4 days ‘labour. In both cases, the relations of wheat and labour to money being given, their mutual relations can be inferred; in other words, we can ascertain that a bushel of wheat is worth 2 days ‘labour. This, which is all that measuring value implies, is as readily done after the reduction as before. The excellence of a thing as a measure of value is altogether independent of its own variableness in value” (p. 11, Bailey, “Money and its Vicissitudes.” London, 1837).