It is easier to practice intermittent than to practice constant restraint.
It is just here that Malthus failed to anticipate the future. Malthus believed that "moral restraint" would lessen the marriage rate, but would have no direct effect on the fecundity of marriage.
A man would not put upon himself the self-denial and restraint, which abstinence from marriage implied, for a longer period than he could help.
The greater the national prosperity, therefore, the higher the birth-rate. But prosperity keeps well in advance of the birth-rate; in other words, population, though it still tends to, does not actually press upon the food supply.
If the moral restraint of Malthus be extended so as to include intermittent moral restraint within the marriage bond, then, under one or other, or all of his three checks, vice, misery, and moral restraint, will be found the explanation of the remarkable demographic phenomena of recent years.
Misery will cover deaths from starvation and poverty, the limitation of births from abortion due to hardship, from deaths due to improper food, clothing, and housing; and emigration to avoid hardship.
Vice will cover criminal abortions, limitation of births from venereal disease, deaths from intemperance, etc., and artificial checks to conception. Malthus included artificial checks of this kind under vice (7 ed. of Essay, p. 9.n.), though they have some claim to be considered under moral restraint. But the question will be referred to in a later chapter.
Moral restraint will cover those checks to conception, voluntarily practised in order to escape the burden and responsibility of rearing children—continence, delayed marriage, and intermittent restraint.
No other checks are directly operative.
Misgovernment and the unequal distribution of wealth and land affect population indirectly only, and can only act through one or other or all of the checks already mentioned.