a. Patur (In order of stringency)
I. tarud/ inability
Tosafos: The second mitzvah would, if done, be mevatel the current mitzvah
Ran: Only if it would be mevatel the normal manner of the mitzvah
Rashi: Even if he just has a mere machshava on his mind.
Hagahos Ashri: If abstaining from the 2nd mitzvah would merely improve the performance of the current mitzvah (e.g. resting outside of a succah would allow him to be well-rested for the next day’s mitzvah). –Based on Iggros Moshe’s interpretation
a. Holech L’Tzorech Mamash
I. definition of the travel
Iggros Moshe defines a travel done L’Tzorech Mamash as being something for which you would travel from home (Tei’Shvu/ Tehiu [אּ] K’Ein Ta’Duru), such as going out for commerce (Rashi).
Both the Magen Avraham and the Levush agree that going out B’Derech S’chora, which is categorized by the Iggros Moshe as being L’Tzorech Mamash, is mutar on Succos. Thus the Iggros Moshe poskins that going out L’Tzorech Mamash is mutar.
b. chiyuv to build succah at night
Levush: If he is able to find one easily, he should. However, if he is not able to find one, he would be patur from building his own. (Emek Bracha: He would not only be patur, but it would be asur to do so because it would then be considered melachah b’chol ha’moed. Therefore, if you follow the Levush you wouldn’t be able to be machmir on yourself to build a succah, following the Magen Avraham)
Magen Avraham: If he can’t
find a succah, he would be chayav to build his own.
Rema: When not being able to find a succah easily, we can say that you are patur from having to use one. However, one who is machmir on himself to build one will be blessed.
Chayei Adam: The Rema’s words seem to say that we follow the Levush and wouldn’t make sense according to the Magen Avraham.
Biur Halachah: Indeed the Rema meant that we follow that the Levush, but if one wishes to follow the Magen Avraham, ‘tavo alav bracha’ (which is difficult according to the Emek Bracha; see above).
Several Achronim: The reason we follow the Levush is because of Shvu K’Ein Ta’Duru: a person will not start building a house at midnight just for somewhere to sleep! [ב]
Emek Bracha: Either way you go you will encounter a paradox in which you must forfeit one mitzvah in order to do the other. There is no way to clearly poskin the safek, with achronim ruling both ways. Thus, it is asur to go on the road to begin with. [גּ]
a. Iggros Moshe Everyone agrees that traveling for personal benefit in an area where there's no succah is strictly asur.
[אּ] The word "tehiu" would make more sense in the context of the term 'TeiShvu K'Ein Ta'Duru.' "Tei'Shvu" implies that the sitting in the succah should be like the sitting at home. However, "tehiu" is a much more general term, meaning that any actions taken in connection to the succah (as opposed to just the sitting) must be based upon actions taken at home.
[ב] This reasoning would imply that it is because of inconvenience that he would not be obligated to build the succah at night. Accordingly, if you have a Pop-a-Succah or something similar which does not take time to build, you would be chayav to build it. Thus, this kulah only applies to succahs that take long or are inconvenient to put up.
[[גּ Rav Bechhofer dislikes this “chop” on the basis that neither the Mishnah Berurah nor anyone else brings up the idea of melachah b’chol ha’moed being connected to this sugya, meaning that it is obviously not relevant