"Scarcely had the Eighteenth Century passed away when it was decisively proved that the reward of labor depends solely on two things; namely, the magnitude of that national fund out of which all labor is paid, and the number of laborers among whom the fund is to be divided. This vast step in our knowledge is due, mainly, though not entirely, to Malthus, whose work on population, besides marking an epoch in the history of speculative thought, has already produced considerable practical results, und will probably give rise to others more considerable still. It was published in 1798; so that Adam Smith, who died in 1790, missed what to him would have been the intense pleasure of seeing how, in it, his own views were expanded rather than corrected. Indeed, it is certain that without Smith there would have been no Malthus; that is, unless Smith had laid the foundation, Malthus could not have raised the superstructure."
The famous doctrine which ever since its enunciation has so powerfully influenced thought, not alone in the province of political economy, but in regions of even higher speculation, was formulated by Malthus in the proposition that, as shown by the growth of the North American colonies, the natural tendency of population is to double itself at least every twenty-five years, thus increasing in a geometrical ratio, while the subsistence that can be obtained from land "under circumstances the most favorable to human industry could not possibly be made to increase faster than in an arithmetical ratio, or by an addition every twenty-five years of a quantity equal to what it at present produces." "The necessary effects of these two different rates of increase, when brought together," Mr. Malthus naïvely goes on to say, "will be very striking." And thus (Chap. I) he brings them together:
