For just as physicians who care for the body believe that the body cannot get any benefit from any food offered to it until all obstructions are removed, so, my boy, those who purge the soul believe that the soul can receive no benefit from any teachings offered to it until someone by cross-questioning reduces him to an attitude of modesty, by removing the opinions that obstruct the teachings, and thus purges him and makes him think that he knows only what he knows, and no more […] For these reasons, Theaetetus, we must assert that cross-questioning is the greatest and the most efficacious of all purifications, and that he who is not cross-questioned, even though he be the Great King, has not been purified of the greatest taints, and is therefore uneducated and deformed in those things in which he who is to be truly happy ought to be most pure and beautiful. (Sophist)
