The present article tries to identify philosophical similar aspects in the investigation around the nature of the true knowledge through the criticism to the rhetorical sophistry in the texts of the speech “Against the Sophists ”, of Isocrates, and of dialog “ Phedro”, of Plato, articulating his perspectives so to find similar points in theirs respective examinations about what is understood like true knowledge, from the criticism that both thinkers do to the sophists who specialized in the development of the (...) political eloquence as well as to who contented himself with writing manuals of rhetoric. (shrink)