Beginning at 293B in Plato’s Euthydemus, Crito asks Socrates if Euthydemus was able to reveal anything to him yesterday at the Lyceum when they spoke in front a crowd of rowdy supporters of Euthydemus. Socrates exclaims that ‘of course!’ that Euthydemus had shown him things.
Euthydemus asks Socrates whether he knows anything to which Socrates responds affirmatively -affirming that he has knowledge, even though elsewhere Socrates frequently claims that he knows nothing. In proceeding Euthydemus’s line of reasoning proceeds as follows: if you have knowledge, then you must have knowledge of something. If you have the means of knowing something it is by the means of the soul, through which you know all things. Then if one knows anything, one must also know consequently know everything, since knowledge comes from within. One must have always known everything. Euthydemus’s argument makes learning impossible (recall Socrates claim that knowledge is recollection in the Phaedrus and the Meno –a happy medium between the claim that man knows everything and the claim that man knows nothing. In both cases knowledge is rendered meaningless).
Similar to Protagoras’s claim that ‘man is the measure of all things’ Euthydemus claims is that man knows absolutely everything, and consequently he also learns nothing, which is an apathetic argument in favor of stultification. However, unlike Heraclitus’s claims that man can never know anything because all things are in a constant state of change (i.e. ‘you can never step into the same river twice’) Euthydemus makes an equally lazy claim that man never learn anything because if he knows at least one thing, then he has learned the knowledge of everything by means of soul and has nothing new under the sun to learn.