What, exactly, did HaSh-m mean by, "the fourth generation"?
Rashi and Targum Yonasan: The fourth generation starting from Yaakov, who went down to Egypt - Yehudah, 1 Peretz, Chetzron and Calev (and Calev entered Eretz Yisrael). 2
Ramban and Rashbam: Only upon the fourth generation of the sinning Kena'anim, would Bnei Yisrael return. It is the way of HaSh-m to "visit the sins of the fathers on the children, the grandchildren and the great-grandchildren," 3 to give them a chance 4 to do Teshuvah. 5
Why doesn't Yaakov count as the first generation? Refer to 15:16:1.1.
But refer to 15:16:1.1:3*.
Since they would not return until four hundred years, the number of generations (of Yisrael) makes no difference. In fact, the four generations (of Kena'anim) plus the reason for the delay given in the Pasuk itself (their sin is not yet complete) explains why they had to wait four hundred years (Rashbam).
This proves that Teshuvah is applicable to Nochrim.
Why does the Torah mention specifically the Emori?
Ramban #1: They were the strongest of the Kena'ani nations.
Ramban #2: They (Sichon and Og) were the first that Yisrael captured.
QUESTIONS ON RASHI
Rashi writes: "'The fourth generation shall return here' -Go and calculate Yaakov's generations - Yehudah, Peretz, Chetzron - and Calev reached Eretz Yisrael." But if we include Yaakov, who also descended to Mitzrayim, then Calev would be the fifth generation?
Riva #1; Mizrachi #1; Chizkuni: Yaakov was already elderly (age 130), and close to his demise, when he went down to Mitzrayim, so he is not counted.
Riva #2; Mizrachi #2: We are not counting the generations from the exile, but rather from when the actual servitude began, which was after Yaakov's death (Rashi to 47:28). 1
Gur Aryeh: "The fourth generation" means after going down to exile, i.e. not including Yaakov. 2
Sifsei Chachamim resolves this with Shemos 1:6, which connotes that the servitude began only later, after all Yaakov's sons died.
See Ohr ha'Chayim, who counts the four generations differently. Also, Malbim questions the assertion that Calev ben Chetzron is one and the same as Calev ben Yefuneh who entered Eretz Yisrael (see also Radak to Divrei ha'Yamim I 2:18, Malbim to ibid. v. 42), and gives other explanations of our Pasuk. (CS)
