Having, in Books I and II, laid out his analysis of the progress of opulence, and having in Book III offered empirical evidence that his analysis is a valuable tool for understanding the actual course of human history, in Book IV Smith examines the strengths and weaknesses of the contemporary, competing models of political economy: the Mercantile system and Physiocracy.

“INTRODUCTION”

Political œconomy, considered as a branch of the science of a statesman or legislator, proposes two distinct objects; first, to provide a plentiful revenue or subsistence for the people, or more properly to enable them to provide such a revenue or subsistence for themselves; and secondly, to supply the state or commonwealth with a revenue sufficient for the publick services. (WN, 428)

This statement reflects three central principles in Smith's moral philosophy.

His assertion that the proper role of the “statesman or legislator” is not to provide for the people but rather “to enable them to provide … for themselves” reflects his deeply held conviction that the secure independence afforded by “the liberal plan of equality, liberty and justice” (WN, 664) empowers people.

Citing as one of the “objects” of political economy the realization of a “ plentiful revenue or subsistence for the people” (emphasis added) reflects his belief that the well-being of the general population is the metric of a good society.

And finally, that a system of political economy must “supply the state or commonwealth with a revenue sufficient for the publick services” reflects his view that there is a role for the state in society. This anticipates Book V, “Of the Revenue of the Sovereign or Commonwealth,” in which he examines the role of the state and how that role should be optimally financed.

His “Introduction” continues: “The different progress of opulence in different ages and nations, has given occasion to two different systems of political œconomy … the system of commerce … [and] that of agriculture” (WN, 428). In Book IV he examines these systems of political economy.