The venerable method of our fathers, which they generally employed towards their sons, and which many still employ, of sometimes showing anger at their errors
and sometimes more gently exhorting them—that would most properly be called as a whole admonition.
That is true.
On the other hand, some appear to have convinced themselves that all ignorance is involuntary, and that he who thinks himself wise would never be willing to learn any of those things in which he believes he is clever, and that the admonitory kind of education takes a deal of trouble and accomplishes little.
They are quite right.
So they set themselves to cast out the conceit of cleverness in another way.
In what way?
They question a man about the things about which he thinks he is talking sense when he is talking nonsense; then they easily discover that his opinions are like those of men who wander, and in their discussions they collect those opinions and compare them with one another, and by the comparison they show that they contradict one another about the same things, in relation to the same things and in respect to the same things. But those who see this grow angry with themselves and gentle towards others, and this is the way in which
they are freed from their high and obstinate opinions about themselves. The process of freeing them, moreover, affords the greatest pleasure to the listeners and the most lasting benefit to him who is subjected to it. For just as physicians who care for the body believe that the body cannot get 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 who is cross-questioned 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.
That is surely the best and most reasonable state of mind.
For all these reasons, Theaetetus, we must assert that cross-questioning is the greatest and 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.