The latter characteristic immediately raises the question of the universality of valuation: Are all things comparable? The idea that every good or service can be substituted to any other one is certainly not spontaneously easy to accept and certainly deserves discussion. Indeed ‘‘substitution’’ may mean replacing the object, substituting the service, maintaining the well-being. The difficulty in replacing technically some goods does not necessarily mean that their derived benefits cannot be compensated in terms of well-being by some other elements.