The use in exchange is a legal phenomenon. Even autometallism is therefore a legal form of the means of payment.
Let us not forget, however, that autometallism is only one instance of means of payment.
Whenever a material, measured in some physical manner, is used as a recognised exchange-commodity, we will call this form authylic (hyle meaning matter). Autometallism is only the most important example of authylism; and authylism itself is only one instance of a means of payment, an instance, namely, where the holder can choose between “real” satisfaction and “circulatory.”
What then is a means of payment? A movable object which can in any case be used for circulation. This, however, is a mere general hint, and you will please note that “real” use should not come into the definition. It would be equally wrong either to demand or to exclude it.
It is difficult to give a correct definition of a means of payment, just as in mathematics we cannot say what a line or a number is, or in zoology define an animal. Often the simplest case (straight line, positive integer) is taken, and one can then proceed to widen the concept, at first recognised in a given example.
Suppose we said, “A means of payment is a movable thing which has the legal property of being the bearer of units of value,” this would be exactly what we mean.
