Plato 's criticism of Protagoras's relativism 9exposed in the Teeteto) outlines two kinds of relativism: the appearance as related to perception, and the appearance as related to action???. By studying the arguments of Plato criticism, and by showing how Plato aims at surpassing those two ways of relativism, the author discovers that the foundation of his criticism is the thought of ideas. Conversely, he himself proposes two different perspectives in an attempt to transcend Protagoras' thesis: From Heralitus' and from Aristotle's. Finally, the author highlights that the Teeteto opens a path for the connection between practical and theoretical philosophy, whose commom root is the appearance.