Many observers view slavery and freedom as polar opposites, but both slave and free wage labor systems rely on compulsion. Slave systems depend ultimately on physical coercion to force slaves to work for masters, although cultural, ideological, and economic pressures typically augment physical force. Wage labor systems, by contrast, depend on workers being free "in the double sense" (Marx [1867] 1967, pp. 168–169): Not only must workers be free to seek employment and choose among potential employers, they also must be free of all other means of subsistence that would allow voluntary withdrawal from the labor market. In the absence of subsistence alternatives, economic necessity compels "free" workers to exchange labor services for wages. Although wage labor systems depend primarily on labor-market processes to supply employers with workers, physical coercion often supplements those processes, especially during periods of economic decline. Cultural expectations and ideological appeals...