Chapter 5 : Whom Could You Marry?
Other aspects of marriage controlled by the Church were questions of who could actually marry. The concepts of consanguinity, a blood relationship, and affinity, which was a relationship by marriage, prevented marriage between close relatives. Marriage, “within the fourth degree” was prohibited, although the method of measuring the degree of relationship changed.
In earlier times the generations up the family tree and then down again were counted separately, so cousins were considered related in the fourth degree. This would make second cousins free to marry. By the late fifteenth century, the practice was to count up to the common ancestor, but not down again, so cousins would be considered related in the second degree and the nearest cousin you could marry would be your fourth cousin.
Repeated intermarriage in the upper classes left most people related by blood or affinity. It was therefore common practice for royalty or nobles to request a dispensation from the Pope to permit marriage within the forbidden degrees. It was generally accepted that the Pope could dispense affinity, as a man-made rule, and also dispense any level of consanguinity that was laid down by Church rules, rather than being specifically mentioned in the Bible, in the book of Leviticus. The Leviticus rules do not stretch to the fourth degree.
(Ed - Without wishing to be cynical about the financial activities of the mediaeval church, one might wonder if the stretching out of the rules of consanguinity reflected the healthy fees payable for a dispensation.)
The whole debate around the validity of the marriage of Henry VIII and Katharine of Aragon centred on whether the relationship between them, formed by her earlier marriage to his brother Arthur, was consanguineous. It would have been considered consanguineous had the marriage been consummated, or merely one of affinity, if it had not. It was clear that the Pope could dispense matters of affinity, but Henry’s argument was that the Pope had no power to dispense a consanguineous relationship that was specifically forbidden in Leviticus.
Although, at the same time, Henry was requesting a dispensation to marry Anne Boleyn, sister of his mistress, Mary and thus in exactly the same relationship to him, or closer, as the relationship with Mary was definitely consummated! Presumably he squared this with his conscious by noting the fact that Leviticus does not comment on the sisters of mistresses.