Socrates

.. is there not one true coin for which all things ought to exchange?- and that is wisdom; and only in exchange for this, and in company with this, is anything truly bought or sold, whether courage, temperance or justice. And is not all true virtue the companion of wisdom, no matter what fears or pleasures or other similar goods or evils may or may not attend her? But the virtue which is made up of these goods, when they are severed from wisdom and exchanged with one another, is a shadow of virtue only, nor is there any freedom or health or truth in her; but in the true exchange there is a purging away of all these things, and temperance, and justice, and courage, and wisdom herself, are a purgation of them.