By Dr. Donald DeMarco, Catholic Exchange - In Book III of the Republic, Plato explains that when the mind is infected by something alien, one of the most serious impairments that results is the mind’s inability to know that it is infected. “Vice cannot know virtue too,” he writes,” but a virtuous nature, educated in time, will acquire a knowledge both of virtue and vice: the virtuous, and not the vicious man has wisdom” (409d).