Volumes 4 and 5 bring together a rich collection of Mill's writing on politics and the economy over the course of his intellectual career. Volume 4 includes, most significantly, 'Essays on Some Unsettled Questions of Political Economy'. Here, Mill grapples with issues related to foreign trade and the balancing of government's goal of promoting free trade with its interest in raising revenues from import duties and tariffs. Also included in these volumes are such early essays as 'The Silk Trade' and 'The Nature, Origin, and Progress of Rent' and such later works as Mill's petition on free trade and 'Chapters on Socialism' (posthumously published).