Rif Succah 1a {Succah 2a-b}

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1a

{Succah 2a}
Mishna:
A succah which is higher that 20 cubits is invalid.
And Rabbi Yehuda considers it valid.
And that which is not 10 handbreadths {high}, or does not have three walls, or whose sun is greater that its shade is invalid.

An old succah - Bet Shammai declare it invalid and Bet Hillel declare it valid.
What is "old"? Any succah made before Succot 30 days. And if he made it for the purpose of Succot, even from the beginning of the year it is valid.

Gemara:
From where do we know these words {that a succah higher than 20 cubits is invalid}?
Rabba said: For the verse states {Vayikra 23:43}:

מב בַּסֻּכֹּת תֵּשְׁבוּ, שִׁבְעַת יָמִים; כָּל-הָאֶזְרָח, בְּיִשְׂרָאֵל, יֵשְׁבוּ, בַּסֻּכֹּת.	42 Ye shall dwell in booths seven days; all that are home-born in Israel shall dwell in booths;
מג לְמַעַן, יֵדְעוּ דֹרֹתֵיכֶם, כִּי בַסֻּכּוֹת הוֹשַׁבְתִּי אֶת-בְּנֵי יִשְׂרָאֵל, בְּהוֹצִיאִי אוֹתָם מֵאֶרֶץ מִצְרָיִם: אֲנִי, יְהוָה אֱלֹהֵיכֶם.	43 that your generations may know that I made the children of Israel to dwell in booths, when I brought them out of the land of Egypt: I am the LORD your God.

Until 20 cubits, one knows {yodea} that he is dwelling {dar} in a succah; higher than 20 cubits, one does not know {yodea} that he is dwelling {dar} in a succah.
What is the reason? Because his eyes do not extend up {to the schach - lit. his eyes do not rule over it}.

Rabbi Zera said: From here {Yeshaya 4:6}:

ו וְסֻכָּה תִּהְיֶה לְצֵל-יוֹמָם, מֵחֹרֶב; וּלְמַחְסֶה, וּלְמִסְתּוֹר, מִזֶּרֶם, וּמִמָּטָר. {פ}

6 And there shall be a pavilion for a shadow in the day-time from the heat, and for a refuge and for a covert from storm and from rain.

Until 20 cubits, one sits in the shade of the succah. Higher than 20 cubits, one does not sit in the shade of the succah but rather in the shade of the walls.

Rava said: From here {Vayikra 23:42}:

מב בַּסֻּכֹּת תֵּשְׁבוּ, שִׁבְעַת יָמִים; כָּל-הָאֶזְרָח, בְּיִשְׂרָאֵל, יֵשְׁבוּ, בַּסֻּכֹּת.

42 Ye shall dwell in booths seven days; all that are home-born in Israel shall dwell in booths;

The Torah states: go from a permanant dwelling and settle in a temporary dwelling. Until 20 cubits, one makes his dwelling a temporary dwelling; higher than 20 cubits, one does not make his dwelling a temporary dwelling but rather a permanant dwelling.

{Succah 2b}
According to Rabba who said that higher than 20 cubits, one does not know that he is dwelling {dar} in a succah because his eyes do not extend to it, if the walls touched the schach, since his eyes do extend to it, even though it is higher than twenty cubits it is valid.

And according to Rabbi Zera who said that higher than 20 cubits, one does not sit in the shade of the succah but rather in the shade of the walls, it it is wider than 4 cubits, since it is wide, the shade of the succah {=schach} exists and it is valid.

And according to Rava who said that higher than 20 cubits, one does not make his dwelling a temporary dwelling but rather a permanant dwelling, there is not any fix to it, but rather, whether the walls reach the schach or the walls do not reach the schach, whether it is wider than 4 cubits, or whether it is not wider than 4 cubits, since it is higher than 20 cubits it is invalid.

There is one who said that the halacha is like Rabba for he always acts in accordance with Rav.

And it makes sense to us that the halacha is like Rava, for we establish that a succah must be a temporary dwelling