Chivalric writers constantly celebrated the importance of keeping one’s word. Ramon Llull said that true knights would not swear false oaths. In Le livre de corps de policie, Christine de Pizan identified being truthful and keeping one’s oath as one of the most important qualities in a knight, and denounced the ignoble vices of dishonesty and the inability to keep a promise. In chivalric romances, the importance of not breaking an oath was a constant theme, and fuelled the dramatic tension when promises and vows to ladies came into direct tension with the requirements of loyal service, as seen in the story of Lancelot and Guinevere, or Tristan’s relationship with Isolde, wife of King Mark. Indeed, the oath taken by the knights of the Round Table in the Vulgate Cycle of Arthurian romances was so central that loyalty usually meant obedience to this specific vow.
Breaking one’s word and the inability to keep a promise were usually associated with youthful or even feminine inconstancy, changeability and weakness. In his book on tournaments, René d’Anjou reported that those guilty of lying and breaking their promises, especially in a matter of honour, were to be removed from their horses, physically assaulted and then publicly shamed by being set on their saddles on top of the list barrier. Breaking an oath was commonly regarded as treason, whether it had been made to a sovereign or not, because it was a betrayal of knighthood itself. —Chivalry and the Ideals of Knighthood in France During the Hundred Years War
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