<b>All these are the twelve tribes of Israel (Gen. 49:28).</b> Elsewhere it is written: <i>Twelve princes shall he beget</i> (Gen. 17:20). These are the number of the tribes, and the world is arranged according to that number. There are twelve hours in the day, and twelve hours in the night. Similarly, there are twelve planets, twelve months in the year, and twelve stones in the ephod. Therefore, <i>all these are the twelve tribes</i>.
R. Yohanan said: Where there actually only twelve tribes? Does it not say: <i>Ephraim and Manasseh shall be like Reuben and Simeon</i> (Gen. 48:5), making fourteen in all? The answer is that when Levi is counted among the tribes, they are not counted, and when Levi is not counted among the tribes, Ephraim and Manasseh are reckoned as one tribe. How do we know this It is written: <i>Of the children of Joseph: of Ephraim, Elishama the son of Manasseh … Gamaliel</i> (Num. 1:10). Hence, <i>all these are the twelve tribes</i>—no more and no less.
Similarly, Rebecca foresaw that there would be twelve tribes, as it is written: <i>And the Lord said to her: Two nations are in thy womb, and two peoples shall be separated from thy bowels</i> (Gen. 25:23). This equals four. <i>And the one people shall be stronger than the other</i> (ibid.); this adds up to six. <i>And the elder will serve the younger</i> (ibid.) makes it eight. When her days to be delivered were fruitful, <i>Behold, there were twins in her womb</i> (ibid., v. 24); this makes ten. <i>The first came forth, and after that his brother</i> (ibid.), totaling twelve in all.
There are others who determine the number of tribes from Rebecca’s use of the word <i>zeh</i> (“thus”); the letters in this word equal twelve arithmetically. When the children struggled together in her womb, she cried out: “Must I suffer like this twelve times, since the Holy One, blessed be He, has told me that twelve children will descend from me?” Then she said: <i>If this be so, wherefore do I live?</i> (ibid., v. 22).