Why did Avraham stop at ten? Why did he not ask for nine to save at least one town from extinction?
Rashi: Because a. he saw how, during the Flood, eight Tzadikim were not able to save the world, and b. he had already tried nine 1 - forty-five for the five towns, which is equivalent to nine for one town, and had not succeeded.
Da'as Zekenim, Hadar Zekenim #1: He thought that there were 10 - Lot, his wife, their four daughters, and their four husbands.
Hadar Zekenim #2: HaSh-m answered that if there are 10 (including Himself), "Lo Ash'chis," but He will not exempt without afflictions. If so, eight and Himself will not help. 2
Gur Aryeh: When did Avraham request this? Avraham had already used the argument of counting 9 righteous individuals and including HaSh-m as 10. If so, all subsequent requests included this argument as well - 27 would count as 30, 18 as 20, and 9 as 10. Also refer to 18:32:2.
Moshav Zekenim connotes that it might save from death, but in any case there will be afflictions, so he did not request.
Why, in fact, did Avraham not ask for thirty-six, twenty-seven, eighteen and nine, to save four, three, two and one town together with Ha'Kadosh-Baruch-Hu (like he asked for forty-five to save the five towns)?
Rashi (according to Ramban): The combination was only acceptable for a large number (five towns), but not for a smaller one. 1
Rashi according to Mizrachi (to 18:29), Ramban: All his future requests were with HaSh-m, 2 and it is obvious that He can similarly join to make forty for four towns, thirty for three, twenty for two and ten for one. 3
As the Midrash says (See Rashi to Vayikra 26:8), 'One cannot compare a few who keep the Torah to many who keep the Torah.'
Also see Gur Aryeh; refer to 18:32:1:1*. 3
In fact the Ramban wonders who prompted Rashi to learn the way he understands that he does.
