e things are in large
measure what we call "substitutes" for one another. An increased
supply, and a lower price of mutton, will probably induce us to
consume less beef. This relation it is convenient to describe as
Composite Supply. Beef and mutton make up a composite supply of meat;
tea and coffee a composite supply of a certain type of beverage. For
any group of things, between which the relation of Composite Supply
exists, we can say, with complete generality, that an increased supply
of one of them will tend to diminish the demand for the
others. Parallel to the relation of Composite Supply is that of
Composite Demand. There are frequently several alternative uses in
which a commodity or service can be employed; and these alternative
uses make up a composite demand for the thing in question. Thus
railways, gasworks, private households and a great variety of
industries contribute to a Composite Demand for coal. It is worth
noting that there is frequently an association in practice between
Joint Demand and Composite Supply on the one hand; and between Joint
Supply and Composite Demand on the other. Wool and mutton, for
instance, we have described as an instance of Joint Supply; but, in so
far as the proportions of wool and mutton can be varied, we can regard
these things as constituting a Composite Demand for sheep. And this
conception may help us to retain a clearer and more orderly picture of
the problems we have discussed above. We can regard the fact that wool
and mutton are produced together as their Joint Supply aspect, and the
fact that these proportions can be varied as their Composite Demand
aspect; and the question as to whether an increased demand for mutton
will increase the supply of wool turns upon whether the former aspect
is more important than the latter. Similarly labor and machinery,
employed together for the same purpose, form an instance of Joint
Demand; but in so far as they can be substituted for one another, they
constitute a Composite Supply of alternative agents of production.

These four relations of Joint Demand, Joint Supply, Composite Demand
and Composite Supply are well worth remembering and distinguishing
from one another. They are of immense importance in every branch of
economic affairs. There are hardly any economic problems upon which we
are fitted to express an opinion, unless we have a lively sense of the
far-reaching ramifications of cause and consequence, of the subtle and
oft