Beginning in 1940’s, as a matter of fact, philosophers, such as Strawson, Austin, Searle, etc, focused on the pragmatic elements in assessing arguments. Toulmin (1958) presents a dialectical model called Toulmin Model different from classical model, which tries to describe the structure of argument as process. However, it is pity that their works had little on the formal semantics developed by Richard Montague and his followers until the rise of Informal Logic (in North America), Pragma-Dialectics (in Holland), and Radical Argumentativism (in France). This paper tries first to evaluate Formal Logical Model, Informal Logical Model and Pragma-dialectical Model of argumentation evaluation, and then construct a Defeasible Pragma-Dialectical Model by introducing Defeasible Modus Ponens rule in order to evaluate a real argument as process in everyday life.
