Exchangeability and value are different characteristics of goods.
For this presupposes the exchangeability of the component parts.
Value is an essential precondition of exchangeability, but can exist without it.
It is absolute social value which I am here distinguishing from exchangeability.
But the theory of exchangeability is a separate matter, and cannot be deduced from the theory of value alone.
It is due Menger to point out that he does not make the distinction between value and exchangeability which I have just made.