Every Thai freeman has to be registered…

Every Thai freeman has to be registered as a servant, or phrai, with the local lord, or nai, for military service and corvée labor on public works and on the land of the official to whom he is assigned.

The phrai can also meet his labor obligation by paying a tax.

If he finds the forced labor under his nai repugnant, he can sell himself into slavery to a more attractive nai, who then pays a fee to the government in compensation for the loss of corvée labor.

As much as one-third of the manpower supply into the nineteenth century will be composed of phrai.