In one of the Soldiers of Fortune stories a couple needs a papal dispensation in order to marry. This is because they’re too closely related to marry in the normal course of things. There were rules about consanguinity which were fairly closely observed by monarchs and the nobility, who would not want anyone to question the validity of a marriage and, by implication, the legitimacy of any heirs. These rules were probably more or less ignored by everyone else.
A papal dispensation is permission from the pope for someone to do something contrary to canon law. Its best-known use relates to marriage, where it can permit a marriage which would not otherwise be allowed or dissolve a marriage.
Probably the most famous papal dispensation was one that wasn’t granted. Henry VIII requested one to enable him to put aside his wife, Katherine of Aragon, and marry Anne Boleyn. Since he had already requested, and received, one in order to marry Katherine, he was on a bit of a losing wicket from the start. Henry had needed a dispensation to marry Katherine because she was his brother’s widow, which meant that their marriage would be incestuous. Katherine said that her marriage to Prince Arthur had not been consummated and the pope allowed Henry and Katherine to marry.
There were prohibitions against marriages considered incestuous and the rules of consanguinity also covered people who were only related by marriage. Hence, if Katherine’s marriage to Arthur had been ruled valid, Katherine and Henry would have been related to the first degree, that is, they would have been considered brother and sister.
The prohibited degrees of consanguinity varied throughout the Middle Ages. Before 1215, when the Fourth Lateran Council clarified the issue, marriage between sixth cousins was prohibited. Who is your sixth cousin? It’s someone who shares a great-great-great-great-great-grandparent with you, or someone who was married to someone who shared a great-great-great-great-great-grandparent with you. You can see how it might be difficult to know who your sixth cousin was. If you lived in a small village, you could almost guarantee that you were related to everyone else more closely than that.
In 1215 the Fourth Lateran Council decreed that the fourth degree of consanguinity was the closest at which a marriage could be permitted. This meant that marriage between a couple who shared a great-grandparent was not permitted. Brother and sister are related in the first degree, first cousins in the second, second cousins in the third and so on. An infringement of this rule was considered incest.
If you were a noble, however, you might be able to persuade the pope that your close relationship to your intended wife was not such an impediment. Edward of Woodstock, the Black Prince, needed a papal dispensation to marry Joan of Kent. His great-grandfather, Edward I, was her grandfather, which meant that they were first cousins once removed. They married secretly some weeks before the dispensation was requested in the hope of forcing the pope’s hand. The pope gave his permission and Joan’s third marriage reinforced her reputation of marital irregularity.