necessarily limited by food; (2) Population always increases where food
increases and tends to increase faster than food; (3) The checks that
keep population down to food supply may be classified as positive and
preventive. Positive checks are those which increase the death rate,
such as famine, poverty, vice, disease, and the like. Preventive checks
are those that decrease the birth rate, such as late marriage and
prudence in the birth of children. Inasmuch as Malthus believed that the
positive checks must always operate where the preventive checks did not,
he advocated the use of the preventive checks as the best means to
remedy human misery. The inherent tendency of population to outstrip
food supply, Malthus believed to be the main source of human misery in
all of its forms.

_Criticisms of Malthus's Theory._ (1) It is evident that Malthus's
theory applies only to a stationary society, that is, a non-progressive
society, because in a progressive society human invention and,
therefore, food supply, may far outstrip any increase of population.
This has been the case in practically all civilized countries during the
nineteenth century, where improvements in machinery and agriculture have
greatly increased the food supply. If it be replied that this increase
of food is but temporary, and that sooner or later Malthus's theory must
operate, then it may be said, on the other hand, that as yet we see no
limit of man's mastery over nature, and that apparently we are just
entering upon the stage of material progress. Moreover, so far as any
given country is concerned, wealth is potential food supply, and in the
United States during the last fifty years wealth has increased four
times as fast as the population. Malthus, of course, did not foresee the
inventions and agricultural progress of the nineteenth century. Still,
it is evident that his theory is a static one and cannot be made to
apply to any progressive society.