I propose some changes to the conceptions of argument and of argumentative discussion in Ralph Johnson’s Manifest Rationality (2000). An argument is a discourse whose author seeks to persuade an audience to accept a thesis by producing reasons in support of it and discharging his dialectical obligations. An argumentative discussion (what Johnson calls ‘argumentation’) is a sociocultural activity of constructing, presenting, interpreting, criticizing, and revising arguments for the purpose of reaching a shared rationally supported position on some issue. Johnson’s theory of argumentative discussion, with occasional modifications, is derived from this definition as a sequence of 17 theorems. Argumentative discussion is a valuable cultural practice; it is the most secure route to correct views and wise policies.