Rabbi Isaac the smith

Rabbi Isaac the smith or Isaac Nappaha (Hebrew rav Yitzhak nappaha, רבי יצחק נפחא) was a second generation Galilean Amora. He was a pupil of Johanan bar Nappaha, "son of the smith" Tradition records him teaching in Antioch. Karaite tradition, borrowed from the Rabbanites, credits Isaac with the initiation of the month not by observing the moon, but like the Rabbanites computing according to the rule of lo, bet, dalet, waw which meant that the Passover can never begin on a Monday, or a Wednesday, or a Friday. To Isaac is attributed the parable of forcing a choice between halakhic and haggadic instruction as akin to pulling out both white hairs and black hairs till a man is left bald.