But such consumption is not consistent with the actual habits of the generality of capitalists. The great object of their lives is to save a fortune, both because it is their duty to make a provision for their families, and because they cannot spend an income with so much comfort to themselves, while they are obliged perhaps to attend a counting house for seven or eight hours a day...
... There must therefore be a considerable class of persons who have both the will and power to consume more material wealth then they produce, or the mercantile classes could not continue profitably to produce so much more than they consume.

Book II, Chapter I, On the Progress of Wealth, Section IX, p. 400 (See also: David Ricardo and aggregate demand). - Principles of Political Economy (Second Edition 1836)