The commoners (pyeongmin, 平民) were ordinary people among the yangin (free-born) who were neither yangban nor jungin; they were also called sangmin or yangmin. They made up the largest share of Joseon's population. Most were farmers, alongside merchants who traded and artisans (gongjang) who worked in crafts.
The taxes and state duties that upheld Joseon
Commoners shouldered the real burdens that kept the state running: the land tax (jose), tribute in local products (gongnap), and labor duty (yeok) — both military service and corvée labor mobilized for building fortresses and roads. Unlike the yangban, who were exempt from military service, military duty weighed heavily on commoner men. In the later period it was often paid in cloth (gunpo) instead, and that burden pressed hard on household finances.
Rights on paper, and the reality
In law, commoners were free people eligible to sit the civil service examination. Indeed, in the late Joseon period some commoners who had built up wealth sought to rise through the military or technical exams. But most lacked the time and money to study, so reaching office was rare. They occupied a middle position between nobi and yangban — guaranteed personal freedom, yet bearing heavy state duties.
Late Joseon: the shrinking commoner class
In the late Joseon period, commoners hoping to escape heavy military duty and to raise their standing increasingly bought yangban status through blank warrants and grain payments or forged genealogies. As a result the number of households claiming to be yangban surged, while the share of commoners and nobi relatively declined. The more status was bought and sold, the more the boundaries of the class system faded — a current that led to the legal abolition of the status system in the 1894 Gabo Reform.