First, how does one become a werewolf? In the Middle Ages, it was not a curse passed along by the bite of a werewolf, but either placed on you by a spell, as in the story of William and the Werewolf, or a "lifestyle choice" by putting on a wolf skin. Gerald of Wales tells the story of a priest who encountered a werewolf couple in Ireland who needed last rites for the she-wolf. When the priest refuses, the wolf skin is opened like opening a coat to reveal an old woman.
In the tale of Bisclavret, we do not know how he became a werewolf, but he explains to his wife that he has to hide his clothes so that he can return to them after three days and become human again. In this situation, the werewolf "curse" is innate, and negated after the period is over by wrapping himself in his original human clothing.
The medieval werewolf also retained its human understanding, and did not simply become a ravenous wolf. When a werewolf in medieval tales attacks someone, it is out of a sense of revenge due to wrongs done to the human host. Bisclavret demonstrates this, and I will go into those details next time.
Regarding phases of the moon: Gervase of Tilbury tells the story of Chaucevaire, who transforms according to the phases of the moon; however, it is the dark of the moon, not the light of a full moon. The moon link may also be part of the werewolf condition in Bisclavret because he transforms without his own choice every week for three days. The author does not specify that there is a lunar link—especially since it is each week, not month—but three days is there length of time often attributed to the full moon.
The word werewolf includes the Old English wer- meaning "man." In the Middle Ages, a werewolf is a man who becomes a wolf. Modern horror films often have werewolves, but in many cases they are larger and more monstrous-looking than ordinary wolves, often standing on two legs. For the Middle Ages, the werewolf literally became a wolf, indistinguishable from other wolves until it acted in ways that wolves would not act.
You will see this tomorrow in what is perhaps the best-known werewolf story from the Middle Ages.
