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If he is "borrowing"borrowing" 2 Challas which he cannotcannot eat he cannot make a Brocha on them and it is as if he is only holding the Broken bread as he can only make a Brocha on his own bread Mishna brura Orach Chaim 161,5: 21:

ודע דכהיום שהמנהג שכל אחד מברך לעצמו ברכת המוציא לכאורה לא שייך כלל דין זה אלא כל אחד יברך על פתו שאוכל [מחה"ש]
One does not need to take off the bread belonging to someone else even when it is white and ones bread is black, since everyone only eats their own bread and can anyway only make a Brocho on their own bread

If he can eat one of the whole loaves he should, as he cannot eat a Prusa (broken) instead of a Shaleima (whole) as already noted Shulchan Aruch Orach Chaim 161,1*


*unless he removed the whole loaf from the table just like in Shulchan Aruch Orach Chaim 161,5 where he wants the black bread over the white Pas Palter he cannot make the Brocha on the Black bread which is inferior without removing the white bread first.
Pesach there is a Mitzva to specifically eat "lechem Oni" i.e broken matza SA OC 473,4 so that's why even together with whole matzos we eat the broken one, but not on regular Shabbos.

If he is "borrowing 2 Challas which he cannot eat he cannot make a Brocha on them and it is as if he is only holding the Broken bread as he can only make a Brocha on his own bread

ודע דכהיום שהמנהג שכל אחד מברך לעצמו ברכת המוציא לכאורה לא שייך כלל דין זה אלא כל אחד יברך על פתו שאוכל [מחה"ש]
One does not need to take off the bread belonging to someone else even when it is white and ones bread is black, since everyone only eats their own bread and can anyway only make a Brocho on their own bread

If he is "borrowing" 2 Challas which he cannot eat he cannot make a Brocha on them and it is as if he is only holding the Broken bread as he can only make a Brocha on his own bread Mishna brura Orach Chaim 161,5: 21:

ודע דכהיום שהמנהג שכל אחד מברך לעצמו ברכת המוציא לכאורה לא שייך כלל דין זה אלא כל אחד יברך על פתו שאוכל [מחה"ש]
One does not need to take off the bread belonging to someone else even when it is white and ones bread is black, since everyone only eats their own bread and can anyway only make a Brocho on their own bread

If he can eat one of the whole loaves he should, as he cannot eat a Prusa (broken) instead of a Shaleima (whole) as already noted Shulchan Aruch Orach Chaim 161,1*


*unless he removed the whole loaf from the table just like in Shulchan Aruch Orach Chaim 161,5 where he wants the black bread over the white Pas Palter he cannot make the Brocha on the Black bread which is inferior without removing the white bread first.
Pesach there is a Mitzva to specifically eat "lechem Oni" i.e broken matza SA OC 473,4 so that's why even together with whole matzos we eat the broken one, but not on regular Shabbos.

3 none of that answered the question afaict, but related to an earlier misunderstanding of the question
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The Rif and the Rambam on Pesach say that the Mitzva is specifically to make a Brocho on "poor mans Bread" the broken matza with one Matza i.e less than what you eat on Shabbos and festivals, so you can choose to eat either the broken piece or the whole matza or both. If you made a Brocho on two whole Matzos in addition to that broken Matza you would be eating "rich mans bread" because now you are making a Brocho on two whole Matzos which are available to eat on a regular Shabbos in addition to the broken matza. This is explained in the Gra OC 473,4

דעת הרי"ף פ' ע"פ והרמב"ם בפ"ח מה' חמץ ומצה דא"צ אלא ב' מצות וכ"ד המ"מ והרבה גאונים וכ"ד רמ"מ וכן משמע לישנא דמתניתין הביאו לפניו מצה כו' וכן ממה שנאמר לחם עוני משמע כן דאל"כ אין זה דרך עניות כיון שיש לפניו ב' מצות וגם יש לפניו חצי מצה

The Rema disagrees and holds like the Shulchan Aruch that as long as one eats the broken Matza he has fulfilled Lechem oni (Poor mans bread) despite making a Brocho on 2 whole Matzos as well. So one can keep the 2 whole matzos for the second night.

On Shabbos we don't have a Mitzva to eat the broken Matza because there is no Mitzva of Lechem Oni. If one is borrowing bread that he has permission to eat one cannot eat a Prusa (broken) instead of a Shaleima (whole) as already noted Shulchan Aruch Orach Chaim 161,1, and he would have to remove the whole bread from the table if he has no intention of eating it so he cannot borrow whole loaves, just like in Shulchan Aruch Orach Chaim 161,5 where he wants the black bread over the white Pas Palter he cannot make the Brocha on the Black bread which is inferior without removing the white bread first.

If he is "borrowing 2 Challas which he cannot eat he cannot make a Brocha on them and it is as if he is only holding the Broken bread as he can only make a Brocha on his own bread

ודע דכהיום שהמנהג שכל אחד מברך לעצמו ברכת המוציא לכאורה לא שייך כלל דין זה אלא כל אחד יברך על פתו שאוכל [מחה"ש]
One does not need to take off the bread belonging to someone else even when it is white and ones bread is black, since everyone only eats their own bread and can anyway only make a Brocho on their own bread

The Rif and the Rambam on Pesach say that the Mitzva is specifically to make a Brocho on "poor mans Bread" the broken matza with one Matza i.e less than what you eat on Shabbos and festivals, so you can choose to eat either the broken piece or the whole matza or both. If you made a Brocho on two whole Matzos in addition to that broken Matza you would be eating "rich mans bread" because now you are making a Brocho on two whole Matzos which are available to eat on a regular Shabbos in addition to the broken matza. This is explained in the Gra OC 473,4

דעת הרי"ף פ' ע"פ והרמב"ם בפ"ח מה' חמץ ומצה דא"צ אלא ב' מצות וכ"ד המ"מ והרבה גאונים וכ"ד רמ"מ וכן משמע לישנא דמתניתין הביאו לפניו מצה כו' וכן ממה שנאמר לחם עוני משמע כן דאל"כ אין זה דרך עניות כיון שיש לפניו ב' מצות וגם יש לפניו חצי מצה

The Rema disagrees and holds like the Shulchan Aruch that as long as one eats the broken Matza he has fulfilled Lechem oni (Poor mans bread) despite making a Brocho on 2 whole Matzos as well. So one can keep the 2 whole matzos for the second night.

On Shabbos we don't have a Mitzva to eat the broken Matza because there is no Mitzva of Lechem Oni. If one is borrowing bread that he has permission to eat one cannot eat a Prusa (broken) instead of a Shaleima (whole) as already noted Shulchan Aruch Orach Chaim 161,1, and he would have to remove the whole bread from the table if he has no intention of eating it so he cannot borrow whole loaves, just like in Shulchan Aruch Orach Chaim 161,5 where he wants the black bread over the white Pas Palter he cannot make the Brocha on the Black bread which is inferior without removing the white bread first.

If he is "borrowing 2 Challas which he cannot eat he cannot make a Brocha on them and it is as if he is only holding the Broken bread as he can only make a Brocha on his own bread

ודע דכהיום שהמנהג שכל אחד מברך לעצמו ברכת המוציא לכאורה לא שייך כלל דין זה אלא כל אחד יברך על פתו שאוכל [מחה"ש]
One does not need to take off the bread belonging to someone else even when it is white and ones bread is black, since everyone only eats their own bread and can anyway only make a Brocho on their own bread

If he is "borrowing 2 Challas which he cannot eat he cannot make a Brocha on them and it is as if he is only holding the Broken bread as he can only make a Brocha on his own bread

ודע דכהיום שהמנהג שכל אחד מברך לעצמו ברכת המוציא לכאורה לא שייך כלל דין זה אלא כל אחד יברך על פתו שאוכל [מחה"ש]
One does not need to take off the bread belonging to someone else even when it is white and ones bread is black, since everyone only eats their own bread and can anyway only make a Brocho on their own bread

2 added 581 characters in body
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The Rif and the Rambam on Pesach say that the Mitzva is specifically to make a Brocho on "poor mans Bread" the broken matza with one Matza i.e less than what you eat on Shabbos and festivals, so you can choose to eat either the broken piece or the whole matza or both. If you made a Brocho on two whole Matzos in addition to that broken Matza you would be eating "rich mans bread" because now you are making a Brocho on two whole Matzos which are available to eat on a regular Shabbos in addition to the broken matza. This is explained in the Gra OC 473,4

דעת הרי"ף פ' ע"פ והרמב"ם בפ"ח מה' חמץ ומצה דא"צ אלא ב' מצות וכ"ד המ"מ והרבה גאונים וכ"ד רמ"מ וכן משמע לישנא דמתניתין הביאו לפניו מצה כו' וכן ממה שנאמר לחם עוני משמע כן דאל"כ אין זה דרך עניות כיון שיש לפניו ב' מצות וגם יש לפניו חצי מצה

The Rema disagrees and holds like the Shulchan Aruch that as long as one eats the broken Matza he has fulfilled Lechem oni (Poor mans bread) despite making a Brocho on 2 whole Matzos as well. So one can keep the 2 whole matzos for the second night.

On Shabbos we don't have a Mitzva to eat the broken Matza because there is no Mitzva of Lechem Oni. SoIf one is borrowing bread that he has permission to eat one cannot eat a Prusa (broken) instead of a Shaleima (whole) as already noted Shulchan Aruch Orach Chaim 161,1, and he would have to remove the whole bread from the table if he has no intention of eating it so he cannot borrow whole loaves, just like in Shulchan Aruch Orach Chaim 161,5 where he wants the black bread over the white Pas Palter he cannot make the Brocha on the Black bread which is inferior without removing the white bread first.

If he is "borrowing 2 Challas which he cannot eat he cannot make a Brocha on them and it is as if he is only holding the Broken bread as he can only make a Brocha on his own bread

ודע דכהיום שהמנהג שכל אחד מברך לעצמו ברכת המוציא לכאורה לא שייך כלל דין זה אלא כל אחד יברך על פתו שאוכל [מחה"ש]
One does not need to take off the bread belonging to someone else even when it is white and ones bread is black, since everyone only eats their own bread and can anyway only make a Brocho on their own bread

The Rif and the Rambam on Pesach say that the Mitzva is specifically to make a Brocho on "poor mans Bread" the broken matza with one Matza i.e less than what you eat on Shabbos and festivals, so you can choose to eat either the broken piece or the whole matza or both. If you made a Brocho on two whole Matzos in addition to that broken Matza you would be eating "rich mans bread" because now you are making a Brocho on two whole Matzos which are available to eat on a regular Shabbos in addition to the broken matza. This is explained in the Gra OC 473,4

דעת הרי"ף פ' ע"פ והרמב"ם בפ"ח מה' חמץ ומצה דא"צ אלא ב' מצות וכ"ד המ"מ והרבה גאונים וכ"ד רמ"מ וכן משמע לישנא דמתניתין הביאו לפניו מצה כו' וכן ממה שנאמר לחם עוני משמע כן דאל"כ אין זה דרך עניות כיון שיש לפניו ב' מצות וגם יש לפניו חצי מצה

The Rema disagrees and holds like the Shulchan Aruch that as long as one eats the broken Matza he has fulfilled Lechem oni (Poor mans bread) despite making a Brocho on 2 whole Matzos as well. So one can keep the 2 whole matzos for the second night.

On Shabbos we don't have a Mitzva to eat the broken Matza because there is no Mitzva of Lechem Oni. So one cannot eat a Prusa (broken) instead of a Shaleima as already noted Shulchan Aruch Orach Chaim 161,1, and he would have to remove the whole bread from the table if he has no intention of eating it so he cannot borrow whole loaves, just like in Shulchan Aruch Orach Chaim 161,5 where he wants the black bread over the white Pas Palter he cannot make the Brocha on the Black bread which is inferior without removing the white bread first.

The Rif and the Rambam on Pesach say that the Mitzva is specifically to make a Brocho on "poor mans Bread" the broken matza with one Matza i.e less than what you eat on Shabbos and festivals, so you can choose to eat either the broken piece or the whole matza or both. If you made a Brocho on two whole Matzos in addition to that broken Matza you would be eating "rich mans bread" because now you are making a Brocho on two whole Matzos which are available to eat on a regular Shabbos in addition to the broken matza. This is explained in the Gra OC 473,4

דעת הרי"ף פ' ע"פ והרמב"ם בפ"ח מה' חמץ ומצה דא"צ אלא ב' מצות וכ"ד המ"מ והרבה גאונים וכ"ד רמ"מ וכן משמע לישנא דמתניתין הביאו לפניו מצה כו' וכן ממה שנאמר לחם עוני משמע כן דאל"כ אין זה דרך עניות כיון שיש לפניו ב' מצות וגם יש לפניו חצי מצה

The Rema disagrees and holds like the Shulchan Aruch that as long as one eats the broken Matza he has fulfilled Lechem oni (Poor mans bread) despite making a Brocho on 2 whole Matzos as well. So one can keep the 2 whole matzos for the second night.

On Shabbos we don't have a Mitzva to eat the broken Matza because there is no Mitzva of Lechem Oni. If one is borrowing bread that he has permission to eat one cannot eat a Prusa (broken) instead of a Shaleima (whole) as already noted Shulchan Aruch Orach Chaim 161,1, and he would have to remove the whole bread from the table if he has no intention of eating it so he cannot borrow whole loaves, just like in Shulchan Aruch Orach Chaim 161,5 where he wants the black bread over the white Pas Palter he cannot make the Brocha on the Black bread which is inferior without removing the white bread first.

If he is "borrowing 2 Challas which he cannot eat he cannot make a Brocha on them and it is as if he is only holding the Broken bread as he can only make a Brocha on his own bread

ודע דכהיום שהמנהג שכל אחד מברך לעצמו ברכת המוציא לכאורה לא שייך כלל דין זה אלא כל אחד יברך על פתו שאוכל [מחה"ש]
One does not need to take off the bread belonging to someone else even when it is white and ones bread is black, since everyone only eats their own bread and can anyway only make a Brocho on their own bread

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