The Wealth of Nations by Part 4 Chapter 9 Page 22

to pay the whole expense which the maintenance and employment of the unproductive class costs either the proprietors or themselves. The industry of merchants, artificers, and manufacturers, though in its own nature altogether unproductive, yet contributes in this manner indirectly to increase the produce of the land. It increases the productive powers of productive labour by leaving it at liberty to confine itself to its proper employment, the cultivation of land; and the plough goes frequently the easier and the better by means of the labour of the man whose business is most remote from the plough.

It can never be the interest of the proprietors and cultivators to restrain or to discourage in any respect the industry of merchants, artificers, and manufacturers. The greater the liberty which this unproductive class enjoys,