the Italian
economist, that "#Exchange consists in giving the superfluous for the
necessary#," or, as I should prefer to say, #the comparatively
superfluous for the comparatively necessary#. He who has more than
enough of one article has already enjoyed all the good which that
article can do to him, but he probably needs supplies of other articles.
The exchange, like an act of mercy, blesses both him who gives and him
who receives, because what each receives in exchange is much wanted and
has high utility. In England, for instance, we possess a great deal of
coal, and France produces plenty of good wine. We could have little or
no wine in England unless we got it from France or some foreign country,
and France also is much in want of coal. It is obvious that there is a
great gain of utility if we give some of our comparatively superfluous
coal in exchange for some of the abundant wine of France.

It has been objected to commerce that it is #sterile# and produces no
new goods. There exist neither more nor less coal and wine after they
are exchanged than before. But in political economy we treat of utility
and wealth; the question is whether things are usefully consumed or not.
Now that which is not wealth if it were consumed by one person, becomes
wealth when handed over to another person for consumption. #Though
exchange cannot create the material of wealth, it creates wealth
because it gives utility to the material.#

#72. Value means Proportion in Exchange.# When we speak of the value of
a thing in exchange, we mean how much of some other thing we can get for
it. This of course will depend upon the nature of that other thing.
Obviously, I can get for a shilling much more potatoes than bread, and
bread than beef, and beef than essence of beef. Therefore, when we speak
of the value of a thing, we ought always to say what it is to be valued
by. #The word value only means that so much of one thing is given for so
much of the other#, and it is the #proportion# of these quantities
(Latin _proportio_ from _pro_, in comparison with, and _portio_, share),
which measures the values of the thing. A ton of pig-iron can usually be
got for a quarter of corn; here the proportion is one to one. To get a
ton of copper, we should probably have to give thirty quarters of corn;
here the proportion is that of one to thirty. There cannot be such a
thing as value in exchange, unless there be proportion--so much of one
commodity for so much