Who knows twelve?
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Twelve are the number of lines of a get - a bill of divorce, and this is hinted to by the gematria of the Hebrew word גט, as the first Tosafos in the gemara Gittin writes in the name of Rabbeinu Tam.
And there is another number twelve connected to this one, as explained in the sefer אמרי שפר:
The main reason why there are twelve lines in a get is to allude to the severing of the connection between a man and his wife through this bill of divorce. Because the connection between them comprises twelve things which they are obligated one to the other: The man is obligated in three things - sustenance, clothing and marital relations, and the woman is obligated in the nine things* which are mentioned in the gemara in Kesuvos 59b, and through the giving of a get these twelve things become annulled.
* The Mishnah there lists seven things which include הצעת המטה - making the bed, and the gemara adds three more which also include הצעת המטה, and Rashi and Tosafos explain that there are two types of הצעת המטה. Nevertheless, since they are practically the same thing we can consider them as one and thus she is obligated in nine things, not ten.
אף הוא היה אומר חמשה דברים של שנים עשר חדש. משפט דור המבול שנים עשר חדש. משפט איוב שנים עשר חדש. משפט המצריים שנים עשר חדש. משפט גוג ומגוג לעתיד לבא שנים עשר חדש. משפט רשעים בגיהנם שנים עשר חדש. שנאמר והיה מדי חדש בחדשו:
He also used to say that there are five things that [last] twelve months: The judgment of the generation of the flood, twelve months; The judgment of Job, twelve months; The judgment of the Egyptians, twelve months; The judgment of Gog and Magog in the time to come, twelve months; The judgment of the wicked in hell, twelve months, for it is said, "And it will be from [one] month until the [next appearance of the same] month" (Isaiah 66:23).