In chapter 1 of
The Theory of Money and Credit, Mises explained what money
is (a universally, or at least commonly, used medium of exchange). In chapter 2, Mises explains what money is
not. Contrary to the common fallacy, it is
not a measure of value.
The notion of money as a measure of value as an artifact of the value theory of the "older political economy". By this he means the "classical economics" of Adam Smith, David Ricardo, and John Stuart Mill. The classical economists by and large believed that the value of a good was an objective attribute of the good itself. Economic actors, according to classical theory, exchanged goods if the respective values of the goods were equal (a fallacy that goes back to Aristotle
1). And how do economic actors determine if an objective attribute of one thing is equal to the same objective attribute of another thing? Well, how do you determine equality between other objective attributes (like length, weight, volume, temperature, etc)? You measure, of course! And assuming value is an objective quantitative attribute, it would seem that the best unit of its measurement would be the money unit.
However, the classical economists were entirely backwards in their value theory. Therefore, their conception of money as a measure of value (derived, as it was, from their value theory) was equally backwards. Classical value theory was finally supplanted by what Mises calls "modern value theory" in the late 19th century. By this, Mises means the
subjective marginal utility theory of value. To understand Mises' monetary theory, it is necessary to understand subjective marginal utility. To come to do so, please read the following three comics.