רב אחא בר יעקב

Rav Acha bar Yaakov was a Babylonian amora who appears frequently throughout the Talmud, especially in the masechtot dealing with sacrifices, ritual purity, and the laws of slaughter. He is repeatedly recorded deriving halachic principles directly from scriptural verses—for example, anchoring the definition of “year” in the laws of consecrated animals in the phrase “a lamb in its year” (Niddah 47b, Arakhin 18b, Bekhorot 27b), and grounding the rule that a king the son of a king is not anointed in a verse about the endurance of a dynasty (Keritot 5b). He likewise brought a verse to establish that converts may still be accepted in an era without sacrifices (Keritot 9a).

The cited passages show him active in concrete questions of practice and method: he is associated with a locale (Paponia) where he instituted immersion on the eighth day out of fear of bandits (Niddah 67b), and he is recorded among sages discussing how various matters were physically tested or examined—by sunlight, by water, or by a hair (Chullin 17b, 56a). He frequently raises objections (matkif) to proposed reasonings, as in his challenges concerning the writing of tefillin and the classification of animals (Chullin 119b, 80a). He also interpreted a verse in Ezekiel as referring to the contemplation of idolatry (Chullin 142a). His name appears in numerous tractates including Niddah, Chullin, Keritot, Arakhin, Bekhorot, and Tamid.