But he shall acknowledge the firstborn, the son of the hated, by giving him a double portion of all that is found with him; for he is the first of his strength, the right of the firstborn is his.
English: “He shall acknowledge” — it was taught: “he shall acknowledge” means he shall make him known to others. From here Rabbi Yehudah said: a man is believed to say “this is my firstborn son,” and just as he is believed to say “this is my firstborn son,” so he is believed to say “this is the son of a divorced woman” or “this is the son of a chalutzah.”
On the daf / in context: The father’s public identification of the firstborn is accepted for inheritance purposes. The same reliability extends to other status declarations that affect the child’s standing.
Type of Learning
Derash on “yakir” establishing the father’s credibility.
What Is Learned
A father is believed when he identifies which son is the firstborn (and when he declares other status facts about his children).