INTRODUCTORY

15

any rate, this principle cannot be denied. Whatever altruistic
motives may direct the spending of a man’s income, in the
getting of it he is mainly dominated by self-regarding
motives. In accepting as a datum the prevalence of action
by each man directed to secure his own interests, it must be
observed that this is treated as a fact, not commended or the
opposite. We desire to investigate the tendencies of things
as we find them, and no greater mistake could be made than
to suppose that economics is a kind of gospel of selfishness.
Next come the recognition of the tendencies which lead to
the multiplication of the human species and the conditions
which limit the increase of numbers. The fact that the
extent and fertility of the earth are limited, and that increase
of energy devoted to the cultivation of the soil is not continuously
 repaid by a proportionate increase of product, is,
as has been mentioned, an important fact in its bearing on
numerous problems of social life. An assumption of very
great importance, the existence of which, as an assumption
in economic arguments, is so much taken for granted that it
is frequently overlooked, is that men are capable of judging
of the efficacy of means to an end, and that the easiest means
will be chosen to reach any desired end. This assumption
is as fundamental as the assumption of action from selfregarding
 motives, and it need hardly be remarked that it is
not universally applicable in an absolute sense. If, however,
men are to be treated in our arguments as unreasoning and
unreflecting beings, neither caring nor knowing what results
fow from any particular action, it will be necessary to rely
on our knowledge of habits of action instead of arguing for
intelligent action, for habits change but slowly, and hence a
knowledge of the habits of the past forms a guide for the
future. The principle of the satiability of wants forms also
a practically universal datum in economic discussion. By
this is meant that when a man’s supply of any commodity
increases, his desire for more decreases, and that he arrives
at a point where he prefers to apply any available resources
to procuring supplies of other commodities, rather than to
increase his supply of the particular commodity under consideration.
 This is true of each class of goods in turn,