Productivity and Population
Given an abundance of land, there is a great deal of latitude in what can be produced, both in terms of the identity and quantity of plants that can be sown, livestock can be raised, etc. There is a theoretical limit to the productivity of land, but in the Europe of the author's time it was far from being met.
As such there was great latitude in the choice of the use of land. Man must eat, but there are a wide range of foods that can be raised to sustain life; man needs clothing, but there are a wide range of plant and animal fibers that can produce cloth; man desires to be amused, but there are a wide range of things that can give him amusement.
It is likely good that men do not choose to make the maximum use of their land for the necessities of life, as the population would increase dramatically were there means to sustain more people.
As an example, consider the population of China and India, where people are supported by the cultivation of rice, and given their great attention to agriculture, a single acre can sustain ten or more people. They also clothe themselves in cotton, an acre of which is sufficient for the clothing of five hundred men, given the temperate climate requires clothing as scant as modesty will allow.
It is also a matter of culture, particularly in China, to make as productive use of the land as possible and to raise as many children as their means of sustenance can afford. It is in the nature of crime or sin to allow an acre of land to lie fallow or let it be wasted on a pleasure-garden. As such they draw from the land as much as it can produce and take from the rivers and extraordinary quantity of fish, and the result is a sizable population.
Growing the population to its maximum possible size and putting land to its maximum possible use has tragic consequences when the maximum cannot be sustained. Consider that a single year's bad harvest leads to starvation of thousands and children are "destroyed" by their parents for their inability to feed them. Such misery would not be visited upon them if they exercised a bit of restraint in their production.
Looking to the opposite extreme, the nomadic tribes of America do not cultivate land or raise livestock and must depend on what little sustenance that nature provides by accident, and as such it requires 50 to 100 acres of and to support a single tribesman. A small tribe may have 40 square leagues of territory, and while there are not mass famines there is a constant engagement in "regular and bitter wars" to defend territories. Such is the consequence of the opposite extreme.
The European way of life involves the cultivation of crops and the rearing of animals in a manner far more efficient than the savage tribes yet far less efficient than that of the Asians. In this wide space between the extremes the peasants have many options for their food and clothing, and a great deal of latitude in the inefficient use of land to seek their pleasure.
In his time, land in Europe would yield six times what was sown, such that one-sixths of the crop would be reserved as seed and the remaining five could be consumed. Land must also rest fallow on year in three, producing wheat in one year and barley in the next.
The bare existence of a man who lives of bread and root vegetables, drinks only water, wears coarse linen and wooden shoes, can thereby sustain himself on one and a half acres of land.
The modest existence of one who wears leather shoes and woolen clothing; lives in a modestly appointed home with a bed, a table, chairs and other necessaries; eats every day meat, butter, cheese, bread, vegetables, and the like; and who is modest in his consumption of beer or wine, can still find that four or five acres of land of medium quality is sufficient to sustain him.
If the price, as chief proprietor of land, sought to increase the population of his kingdom, they would encourage productivity and modesty among their people, to raise as much food and necessities as possible and no luxuries, and would thereby gather to themselves great numbers of miserable subjects.
But if instead the prince caused the land to be used for other purposes, the conveniences and luxuries of life, then it would be necessary to devote portions of the land to the productions of goods other than bare necessities, and the number of subjects in his kingdom would be more conservative in their numbers.
The maintenance of a horse, for example, requires as much grain as ten men and pastureland where food for another may have been grown. Therefore to maintain a number of horses is to forego a number of subjects, for what is fed to the horse is denied to the people.
Likewise when the nobility take delight in foreign goods and pays form them with native produce, the price of the imported goods is the withdrawal of goods from domestic consumption (and then increase of goods in foreign lands, which in some instances provides for the sustenance of men who may become enemies of the state).
The link between productivity and population is indirect, but quite effective: a worker who is making scarce enough income to sustain himself is discouraged from raising a family, recognizing that he lacks the means to support them. A worker whose wage exceed his needs will for a time spend the excess on luxury, but will eventually recognize that he has, on an ongoing basis, sufficient resources to marry and raise children, and will be inclined to do so.
This is a general tendency but is not universal: a peasant who is scarce able to support himself may nonetheless make an irresponsible choice to breed children he cannot feed, and another who is able to afford a family may choose to continue to refrain from doing so.
The general tendency in Europe is to be conservative in breeding. The nobility have fewer children than their means can support, and thereby live in affluence. It is the general tendency for the majority of an estate to be passed to the eldest son, but even the younger sons are in no hurry to marry if doing so will decrease their status. Even among he lower classes, people do not bear as many children as is theoretically possible.
It is only in countries where the people are "content to live the most poorly" that the increase in population is a carried the furthest, or in locations such as the colonies where the abundance of fertile land provides ample subsistence, enabling the population to multiply "like mice in a barn."