Both Hamlet and the Ghost repeatedly refer to Gertrudes marriage to her former brother-in-law Claudius not merely as “adulterous” but also as “incestuous.” Why?
The era’s prevalent doctrine did not distinguish between blood relationships and those existing “only” in law; siblings by marriage were, in principle, prohibited from marrying the same way that blood siblings were. Any and all marriages between (former) in-laws required a special canonical dispensation, and although such dispensations were not infrequently granted, their terms could later cause confusion if they contained the slightest ambiguity. Thus, the papal dispensation granted to Henry VIII of England and his first wife Catherine of Aragon, who had briefly been married to Henry’s predeceased elder brother Arthur, was vague both in its terms and its foundation because it was unclear whether Catherine’s and Arthur’s marriage had ever been consummated (only if it had been, a dispensation would have been required): a circumstance which all sides tried to use in their respective favour over twenty years later in the fierce battle over King Henry’s and Queen Catherine’s divorce and th
