Henry VIII (reigned 1509–1547) was granted a dispensation from the impediment of affinity. Today, the impediment of affinity arises between a person and his or her spouse’s direct-line relatives. For example, a widower is impeded from marrying his deceased wife’s mother, grandmother, daughter, granddaughter, etc. (CIC 1092).
In the sixteenth century, though, the impediment of affinity came about merely through intercourse (marriage was not required) and extended further than the direct line of relatives. Since it was presumed that Catherine of Aragon had intercourse with her husband, Henry’s brother, the impediment of affinity had to be dispensed before Catherine and Henry could validly marry.