So (租)

So as well as Zei are the goods and services that the government collect to ensure public finance for the nation. According to Setsumon-kaiji (Shuowen Jiezi) (Explaining Simple and Analyzing Compound Characters), So is defined as "Tax levied on rice crops," which was originally Denso, and was collected nominally for ritual expenses.

So is what is newly collected (Flow), and saved So (Stock) is Zei. Refer to Sozei.

Under the Ritsuryo system (a system of centralized government based on the ritsuryo code), Denso was collected as So. Under So-Yo-Cho (the tax system), only So had the aspect of land tax.