
… It is not to be assumed that we offer for sale articles required for our own consumption. … We wish to part with a useless thing, in order to get one that we need; we want to give less for more. … It was natural to think that, in an exchange, value was given for value, whenever each of the articles exchanged was of equal value with the same quantity of gold. … But there is another point to be considered in our calculation. The question is, whether we both exchange something superfluous for something necessary.
Le Commerce et le Gouvernement (1776), as quoted in Marx's Capital, Vol. I, Ch. 5.