Supply, Demand, Equilibrium

'The Law of Supply and Demand' usually connotes the tendency of the price of a good to reach equilibrium, as a function of the relation between its supply and its demand.  The fundamental concepts of that function are that as Supply increases, Price decreases, and that as Demand increases, Price increases, with more elaborate formulations of them usually the interest of Economists.  One constant in their projections is the 'rational' behavior of participants, conceived as the well-informed seeking to maximize gain and minimize loss in any transaction.  Thus, the actuality of their hypotheses is contingent on the actuality of such behavior.  In any case, any such Law presupposes a relation between Supply and Demand themselves, of which there are three main possibilities--Supply exceeds Demand, Demand exceeds Supply, and Supply and Demand are in equilibrium.  Now, in the case of this Supply-Demand equilibrium, there is no presumption of a inherent tendency towards it.  To the contrary, as in the example of Plato's commensuration between need and work-force, that equilibrium is an ideal.  Accordingly, the best Economic system can be defined as one in which Supply-Demand Equilibrium obtains.