At the end of book 2 of The Once and Future King, T. H. White states that the story of King Arthur is a tragedy in the true Aristotelian sense, according to which most tragic heroes have an inherent flaw that contributes to their “reversal of fortune.” The hero’s tragic flaw is not necessarily a bad quality—Arthur’s flaw, in fact, is his belief in the decency and perfectibility of humanity.

Arthur’s flaw is revealed as the novel moves from descriptions of his innocent childhood to the imperfect, even corrupt world of his adulthood and, finally, to the loss of his kingdom; this movement is the “reversal of fortune” that results from Arthur’s tragic flaw. It is the movement that unites the four narrative strands of the novel. The stories of Gawaine (book 2), Lancelot (book 3), and Mordred (book 4), considered within the framework of Arthur’s own story, illustrate the theme that while some people may be decent, there will always be those who make Arthur’s dreams of a better civilization impossible.

Believing people to be basically good, Arthur establishes the Round Table to destroy the authority of those who rule through brutal force and to impose on humanity the notion of decency. Arthur remains blind, however, to reminders that his vision will fail. He willfully overlooks the affair between Lancelot and Guenever, the murderous depth of Gawaine’s rage, and the evil madness of his son Mordred. If he were to acknowledge deception, rage, and evil in those closest to him, he would have to deny humanity’s perfectibility. Lancelot and Gawaine do turn out to be good and honorable men, however, thus reinforcing Arthur’s convictions.

By nature, Lancelot is not deceptive, but he is weak. As a medieval Christian, he knows that his sinful nature stands in the way of one of his greatest ambitions: to perform a miracle. Lured by Guenever and encouraged by Arthur’s blindness, he can never resist the queen’s seduction and he remains, at least in his own eyes, a weak man. Yet, as he tells Guenever, his awareness of his own flawed nature drives him to be the best knight in the world. Significantly, when he fully accepts his own imperfect nature, he is allowed to perform a miracle by healing Sir Urre of his bleeding wounds.

Gawaine, too, reinforces Arthur’s belief in the goodness of humanity. Gawaine has learned rage, even hatred, from his mother, Morgause, who is consumed by hatred for Uther Pendragon, Arthur’s father, who killed Cornwall, the husband of her mother Igraine. She passes her hatred for the Pendragons on to her sons, and Gawaine pledges to get revenge. Gawaine has an inclination to do good, however. Thus, once he is a knight of the Round Table, Gawaine transfers much of his loyalty to the king. Gawaine knows that Arthur is not an evil man, but he experiences tremendous conflict when Lancelot kills his two brothers while rescuing Guenever. Gawaine vows revenge but eventually overcomes his vindictiveness, forgiving Lancelot and so performing an act nearly as miraculous as Lancelot’s healing of Sir Urre.

The political machinations of Mordred reveal Arthur’s tragic flaw clearly. An extraordinarily bright young man, Mordred is both insane and evil. His mother, Morgause, has taught him to hate Arthur, and, unlike Gawaine, Mordred never relinquishes this hatred. Knowing of Arthur’s belief in the decency of humanity and realizing that his father is fond of him, Mordred easily takes the kingdom from Arthur and shatters Arthur’s world. Indeed, White’s point seems to be that as long as there are Mordreds, the human race will never reach perfection,...