PROOF OF PRIMOGENITURE
In determining the fact of primogeniture reliance is placed upon the statements of three persons – the midwife, the mother, and the father. That the midwife is relied upon immediately after the son's birth (where twins are born) is derived from Genesis 38:28 (see TJ, Kid. 4:2,65d); the mother is relied on during the first seven days after childbirth, since the father has not yet succeeded in "accepting" or recognizing the child, as he does not pass out of his mother's hands until the circumcision; thereafter the father's determination is accepted at all times, since he "must acknowledge his son" – i.e., recognize the child as his firstborn son personally and before others. The father's determination is relied upon even if he thereby assails the status of his other sons, as may happen if he acknowledges as his firstborn the youngest of several sons borne by his wife after they married each other – thus characterizing the other sons as mamzerim (Yev. 47a; Kid. 74a and Posekim ad Lec.; see also Mamzer). However, the father is not believed in this last-mentioned case if the disqualified son already has children of his own, as the disqualification would also affect their status – for which purpose the law does not authorize reliance on his words (Yev. 47a and Posekim; Ozar ha-Posekim, EH, 1 (1955), 192, sec. 4:137).