Why did Noach curse Canaan and not Cham?

Question

After the incident with Cham after the flood, Noach curses Canaan (Genesis 9:25). Why does he not curse Cham, the one who actually wronged him?

The explanations I've seen of this incident have Cham performing inappropriate sexual acts on his father. Today I came across this non-Jewish explanation suggesting that actually, Cham violated Mrs. Noach and Canaan was the product of this, so, like the children of Lot, Canaan was cursed because of his origin. (This explanation would require us to understand the curse as not immediately following the act, of course.) If that's the case then this would explain why the curse is directed at Canaan, but I've never heard that idea from a Jewish source before and it sounds not quite right to me.

What do our sources say about why the curse was directed at Canaan?

(This question is not primarily about what Cham did, but that might affect the answer to my question.)

Answer 1

Among the midrashim we find several opinions as to why Noach cursed K'naan. Here's a few:

• Hashem had already blessed Noach and his sons (9:1) and a curse cannot exist while the blessing stands. He thus could not curse Cham (the actual perpetrator) and cursed his grandson K'naan instead. (Bereshis Rabbah 36:11; R' Yehuda) [As to why K'naan instead of Cham's other sons, perhaps because K'naan was the "main" child of Cham. "חם אבי כנען". Or additionally, see Radak below.]
• K'naan heard about Noach's state and either sodomized him or castrated him. (Midrash cited in commentaries. Yet a similar midrash brought in Talmud Bavli Sanhedrin 70a brings the explanations that Cham was the one who sodomized and/or castrated Noach. Then Noach cursed K'naan in the spirit of "You prevented me from having a fourth child, thus I curse your fourth child".)
• K'naan was the one who originally saw Noach and told his father Cham about it. (Bereshis Rabbah 36:11; R' Nechemia)

R' Saadia Gaon interprets "ארור כנען" as "ארור אבי כנען" - "Cursed be the father of K'naan". [This interpretation is analyzed by Ibn Ezra in his commentary.]

Radak suggests that Noach's intention was to curse Cham and his descendants, but saw trough nevua that the curse would be fulfilled through the descendants of K'naan.

Ralbag believes that K'naan was the one who originally disrobed Noach while he was passed out.

Ibn Kaspi and Shadal suggest that Noach wanted to limit Cham's curse to only a portion of his descendants, and chose K'naan since he was Cham's most beloved child.

Abarbanel writes that K'naan was inseparable from his father; went wherever Cham went and did whatever he did, which is why in the act, he is referred to as "חם אבי כנען" in 9:22. Abarbanel reads the verse as: "Cham, the father of K'naan, saw the nakedness of his father, and he [K'naan] told his two brothers outside." (Although K'naan actually had three brothers, seems he only two were available.) Therefore, although Cham had saw Noach and neglected to act respectfully as Shem and Yefet did, he did not do anything actively wrong like K'naan did.

Answer 2

Daas Z'kenim mibaale hatosafos (ad loc.) cites a midrash that says that K'naan overheard the announcement in verse 22, and went and sodomized Noach. (Cham himself, according to this midrash, did nothing wrong except speak of his father disparagingly and in public.) Verse 24 refers, then, to a grandson as "son" (not uncommon, and makes more sense here than referring to Cham, who was not the youngest).