(Devarim 21:17) "But the first-born, the son of the hated one, shall he recognize": He shall cause him to be recognized by others — whence R. Yehudah ruled: A man is believed to say: This is my first-born son. And just as he is believed to say: This is my first-born son, he is believed to say: This is the son of a chalutzah (a woman taken in levirate marriage); this is the son of a divorcée. The sages say: He is not believed.
"to give him a double portion": A double portion of what each brother receives? Or a double portion of the entire property? You reason thus: Just as he inherits with one brother, and he inherits with five, then just as when he inherits with one he inherits a double portion of one, so, when he inherits with five, he inherits a double portion of one.
Or, go in this direction: Since he inherits with one and he inherits with five, then just as when he inherits with one, he inherits a double portion of all the property, so, when he inherits with five, he inherits a double portion of all the property. It is, therefore, written "then it shall be on the day that he causes his sons to inherit." "inheritance to sons" (and not "inheritance of property") is repeated.
After we learn that inheritance to sons is to be emphasized, we perforce must follow the first approach, viz.: Since he inherits with one (son) and he inherits with five, then just as when he inherits with one, he receives a double portion of one, so, when he inherits with five, he receives a double portion of one. And it is written (I Chronicles 5:1) "And the sons of Reuven, the first-born of Israel (i.e., Jacob). For he was the bechor, but when he defiled his father's bed, his birthright was given to the sons of Joseph." And it is written (Ibid. 2) "For Judah prevailed over his brothers (to inherit the kingship) and the ruler was to come from him, and the bechorah (the status of first-born) was given to Joseph." And it is written (Bereshith 48:22) "And I (Jacob) have given to you (Joseph) an additional portion over your brothers."
Since we find that the bechorah went to Joseph, and the bechorah is for all generations, then just as we find that the bechorah for Joseph was a double portion of one (son), so, the bechorah for all generations is a double portion of one.
"a double portion" in all that is found with him": We are hereby taught the bechor does not take a double portion of what is anticipated as he does of what is on hand.
(דברים כא יז) כִּי אֶת הַבְּכֹר בֶּן הַשְּׂנוּאָה יַכִּיר – יַכִּירֶנּוּ לַאֲחֵרִים, מְלַמֵּד שֶׁנֶּאֱמָן אָדָם לוֹמַר ׳זֶה בְּנִי בְּכוֹר׳. רַבִּי יְהוּדָה אוֹמֵר: כְּשֵׁם שֶׁנֶּאֱמָן אָדָם לוֹמַר ׳זֶה בְּנִי בְּכוֹר׳, כָּךְ נֶאֱמָן לוֹמַר ׳זֶה בֶּן גְּרוּשָׁה וְזֶה בֶּן חֲלוּצָה׳, וַחֲכָמִים אוֹמְרִים: אֵינוֹ נֶאֱמָן.
(Devarim 21:17) "But the first-born, the son of the hated one, shall he recognize": He shall cause him to be recognized by others — whence R. Yehudah ruled: A man is believed to say: This is my first-born son. And just as he is believed to say: This is my first-born son, he is believed to say: This is the son of a chalutzah (a woman taken in levirate marriage); this is the son of a divorcée. The sages say: He is not believed.
לָתֶת לוֹ פִּי שְׁנַיִם – פִּי שְׁנַיִם בּוֹ. אוֹ פִּי שְׁנַיִם בְּכָל הַנְּכָסִים? הֲרֵי אַתָּה דָן: הוֹאִיל וְנוֹחֵל עִם אֶחָד וְנוֹחֵל עִם חֲמִשָּׁה, מַה מָּצִינוּ כְּשֶׁנּוֹחֵל עִם אֶחָד – פִּי שְׁנַיִם בּוֹ, אַף כְּשֶׁנּוֹחֵל עִם חֲמִשָּׁה – פִּי שְׁנַיִם בְּאֶחָד מֵהֶם.
"to give him a double portion": A double portion of what each brother receives? Or a double portion of the entire property? You reason thus: Just as he inherits with one brother, and he inherits with five, then just as when he inherits with one he inherits a double portion of one, so, when he inherits with five, he inherits a double portion of one.
אוֹ כַּלֵּךְ לְדֶרֶךְ זוֹ: הוֹאִיל וְנוֹחֵל עִם אֶחָד וְנוֹחֵל עִם חֲמִשָּׁה, מַה מָּצִינוּ כְּשֶׁנּוֹחֵל עִם אֶחָד – פִּי שְׁנַיִם בְּכָל הַנְּכָסִים, אַף כְּשֶׁנּוֹחֵל עִם חֲמִשָּׁה – פִּי שְׁנַיִם בְּכָל הַנְּכָסִים! תַּלְמוּד לוֹמַר: ״וְהָיָה בְּיוֹם הַנְחִילוֹ אֶת בָּנָיו״, רִבָּה נַחֲלָה לַבָּנִים.
Or, go in this direction: Since he inherits with one and he inherits with five, then just as when he inherits with one, he inherits a double portion of all the property, so, when he inherits with five, he inherits a double portion of all the property. It is, therefore, written "then it shall be on the day that he causes his sons to inherit." "inheritance to sons" (and not "inheritance of property") is repeated.
אַחַר שֶׁלָּמַדְנוּ שֶׁרִבָּה נַחֲלָה לַבָּנִים, הָא אֵין עָלֶיךָ לָדוּן אֶלָּא כַּדִּין הָרִאשׁוֹן: הוֹאִיל וְנוֹחֵל עִם אֶחָד וְנוֹחֵל עִם חֲמִשָּׁה, מַה מָּצִינוּ כְּשֶׁנּוֹחֵל עִם אֶחָד – פִּי שְׁנַיִם בּוֹ אַף כְּשֶׁנּוֹחֵל עִם חֲמִשָּׁה – פִּי שְׁנַיִם בְּאֶחָד מֵהֶם. וְכֵן הוּא אוֹמֵר (בראשית מח כב): ״וַאֲנִי נָתַתִּי לְךָ שְׁכֶם אַחַד עַל אַחֶיךָ״, וְאוֹמֵר (דברי הימים א ה א-ב): ״וּבְנֵי רְאוּבֵן בְּכוֹר יִשְׂרָאֵל כִּי הוּא הַבְּכוֹר״ וְאוֹמֵר: ״כִּי יְהוּדָה גָּבַר בְּאֶחָיו וּלְנָגִיד מִמֶּנּוּ, וְהַבְּכוֹרָה לְיוֹסֵף״.
After we learn that inheritance to sons is to be emphasized, we perforce must follow the first approach, viz.: Since he inherits with one (son) and he inherits with five, then just as when he inherits with one, he receives a double portion of one, so, when he inherits with five, he receives a double portion of one. And it is written (I Chronicles 5:1) "And the sons of Reuven, the first-born of Israel (i.e., Jacob). For he was the bechor, but when he defiled his father's bed, his birthright was given to the sons of Joseph." And it is written (Ibid. 2) "For Judah prevailed over his brothers (to inherit the kingship) and the ruler was to come from him, and the bechorah (the status of first-born) was given to Joseph." And it is written (Bereshith 48:22) "And I (Jacob) have given to you (Joseph) an additional portion over your brothers."
הוֹאִיל וּמָצִינוּ שֶׁהַבְּכוֹרָה לְיוֹסֵף וּבְכוֹרָה לְדוֹרוֹת, מַה בְּכוֹרָה הָאֲמוּרָה לְיוֹסֵף – פִּי שְׁנַיִם בּוֹ, אַף בְּכוֹרָה הָאֲמוּרָה לְדוֹרוֹת – פִּי שְׁנַיִם בְּאֶחָד מֵהֶם.
Since we find that the bechorah went to Joseph, and the bechorah is for all generations, then just as we find that the bechorah for Joseph was a double portion of one (son), so, the bechorah for all generations is a double portion of one.
בְּכֹל אֲשֶׁר יִמָּצֵא לוֹ, מְלַמֵּד שֶׁאֵין הַבְּכוֹר נוֹטֵל בָּרָאוּי כְּבַמּוּחְזָק.
"a double portion" in all that is found with him": We are hereby taught the bechor does not take a double portion of what is anticipated as he does of what is on hand.
כִּי הוּא רֵאשִׁית אוֹנוֹ – וְלֹא רֵאשִׁית אוֹנָהּ שֶׁל אִשָּׁה.
"for he is the first of his (the father's) strength": and (the criterion for bechorah is) not the first of her (the mother's) strength.
לוֹ מִשְׁפַּט הַבְּכֹרָה – מְלַמֵּד שֶׁהַבְּכוֹרָה יוֹצְאָה בְדַיָּנִים.
"his is the judgment of the bechorah": We are hereby taught that the double portion of the bechorah can (if necessary) be appropriated by the courts.