Why 14 days? TB Baba Batra 111

One of the 13 different methods of expounding the Torah is a kal vekhomer (מִקַּל וָחֹֽמֶר), a fortiori inference, a conclusion drawn from a minor or lenient law, to a major or more strict one. This method is capped by the principle of diyo (דַּיּוֹ), it is sufficient. “According to this principle, a halakha derived by means of an a fortiori inference cannot go beyond the halakhot of the source from which it is derived.” (TB Baba Batra 111, Sefaria.org translation) Today’s daf TB Baba Batra 111 teaches us that

“It is sufficient (the principle of diyo), which limits the extent of a fortiori inference, is found in the Torah. As it is taught in a baraita that explains the hermeneutical principles: How does an a fortiori inference work? The verse states with regard to Miriam, after she spoke ill of her brother Moses: “And the Lord said to Moses: If her father had but spit in her face, should she not hide in shame seven days?” (Numbers 12:14). The verse is saying that if a father spits in the face of his daughter and reprimands her, she would feel shame for seven days. By an a fortiori inference it is derived that Miriam, who suffered the more severe reprimand of the Divine Presence, should be ostracized for fourteen days. Why then, was Miriam ostracized for only seven days? Rather, it is sufficient for the conclusion that emerges from an a fortiori inference to be like its source, so her punishment cannot be for longer than the punishment of one who is reprimanded by a father.” (Sefaria.org translation)

The Rishonim discuss why the kal vekhomer comes to the conclusion that Miriam deserved to be punished for 14 days. Some even argue that the ostracization shall last forever. Rebbeinu Tam explanation is based on a Gemara in TB Nedah 31a. There are three partners in the conception of a child, the Holy One Blessed be He, the father, and the mother. Since God’s portion of providing the soul and animation is compared to both of the contributions of the father and the mother, God’s portion is worth double. Consequently, God’s reprimand should be double the ostracization of seven days for a parent.

The Ritba and others explain that God’s honor demands more time than that of the parent. Since Miriam came down with tzara’at, a skin disease which demands the person leave the camp for seven days, these seven days are added upon the first to equal14 days.

Ramban explains that this is the normal style of Midrash Halakha to double the amount when learning from a kal vekhomer.