He profited by his observation, and by the writings of his critics, and published his matured work in 1803.
The distinguishing feature about this edition was the addition of moral restraint as a check, to the two already described, vice and misery.
Malthus maintained that population has the power of doubling itself every 25 years.

Not that it _does_ so, or _had done_ so, or _will do so_, but that it is _capable_ of doing so, and he instanced the American Colonies to prove this statement.
One would scarcely think it was necessary to enforce this distinction, between what population has done, or is doing, and what it is capable of doing.

But when social writers, like Francesco Nitti (Population and the Social System, p.

90), urge as an argument against Malthus's position that, if his principles were true, a population of 176,000,000 in the year 1800 would have required a population of only one in the time of our Saviour, it is necessary to insist upon the difference between _increase_ and the _power of increase_.
One specific instance of this doubling process is sufficient to prove the _power of increase_ possessed by a community, and the instance of the American Colonies, cited by Malthus, has never been denied.
A doubling of population in 25 years was thus looked upon by Malthus as the normal increase, under the most favourable conditions; but the checks to increase, vice, misery, and moral restraint are operative in varying degrees of intensity in civilized communities, and these may limit the doubling to once in 50, or once in 100 years, stop it altogether, or even sweep a nation from the face of the earth.
The natural increase among the lower animals is limited by misery only, in savage man by vice and misery only, and in civilized man by misery, vice, and moral restraint.
Misery is caused by poverty, or the need of food or clothing, and is thus proportionate to the means of subsistence.

As the means of subsistence are abundant, misery will be less, the death-rate lower, and _caeteris paribus_ the birth-rate higher.