two ceremonial forms serving to bring useful value and
exchangeable value face to face, and to provoke their
reconciliation. They are the two electric poles, whose
connection must produce the economical phenomenon of affinity
called EXCHANGE. Like the poles of a battery, supply and demand
are diametrically opposed to each other, and tend continually to
mutual annihilation; it is by their antagonism that the price of
things is either increased, or reduced to nothing: we wish to
know, then, if it is not possible, on every occasion, so to
balance or harmonize these two forces that the price of things
always may be the expression of their true value, the expression
of justice. To say after that that supply and demand is the law
of exchange is to say that supply and demand is the law of supply
and demand; it is not an explanation of the general practice, but
a declaration of its absurdity; and I deny that the general
practice is absurd.

I have just quoted Ricardo as having given, in a special
instance, a positive rule for the comparison of values: the
economists do better still. Every year they gather from tables
of statistics the average prices of the various grains. Now,
what is the meaning of an average? Every one can see that in a
single operation, taken at random from a million, there is no
means of knowing which prevailed, supply--that is, useful
value--or exchangeable value,--that is, demand. But as every
increase in the price of merchandise is followed sooner or later
by a proportional reduction; as, in other words, in society the
profits of speculation are equal to the losses,--we may regard
with good reason the average of prices during a complete period
as indicative of the real and legitimate value of products. This