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ON THE CAUSES

value to B, this must be owing, not only to
causes operating on a, but also to causes operating
 on B. In investigating the sources of
value, however, it will be necessary to treat of
these causes separately; and it may not be
useless to recollect, that although value must
in every instance arise from the combination of
two sets of causes, any alteration, any rise or
fall of value, may proceed from only one. The
value of A and B is the effect of causes acting
on both, but a change in their mutual value may
arise from causes acting on either : as the distance
of two objects is to be referred to the circumstances
 which have fixed both of them in their
particular situation, while an alteration of the
distance between them might originate in circumstances
 acting on one alone.
What then are the causes which determine
the value of commodities, and an alteration in
which is followed by a change in their relations?
 Or, in other words, what are the causes
which determine the quantities in which commodities
 are exchanged for each other?