“Oath-breaker.” In the mystical and now-familiar world of J.R.R. Tolkien’s fantasy, a person’s word was his bond. An oath, once uttered, could gain a transcendent power of its own, bonding the oath taker to the oath’s object. Men and women ignored that power only at their extreme peril; a broken oath could even condemn the swearer to living death—an eternity of wandering the earth, pursued by furies, unable to find final rest until the swearer atoned, and the broken oath was ultimately fulfilled. “Oath-breaker” was accordingly one of the harshest insults that could be leveled against an individual, an invective spat out against people the speaker deemed to be the truly lowest of the low....