A feather will weigh down a scale when there is nothing in the opposite one.

In general it may be said that demand is quite as necessary to the increase of capital as the increase of capital is to demand.

The ordeal of virtue is to resist all temptation to evil.

The world's population will multiply more rapidly than the available food supply.

[P]opulation, when unchecked, goes on doubling itself every twenty-five years, or increases in a geometrical ratio. ... [T]he means of subsistence, under circumstances the most favorable to human industry, could not possibly be made to increase faster than in an arithmetical ratio.

The immediate cause of the increase of population is the excess of the births above deaths; and the rate of increase, or the period of doubling, depends upon the proportion which the excess of the births above the deaths bears to the population.

The passion between the sexes has appeared in every age to be so nearly the same, that it may always be considered, in algebraic language as a given quantity.