Genesis 9:20-25 tells us, "Noah, a man of the soil, proceeded to plant a vineyard. When he drank some of its wine, he became drunk and lay uncovered inside his tent. Ham, the father of Canaan, saw his father’s nakedness and told his two brothers outside. But Shem and Japheth took a garment and laid it across their shoulders; then they walked in backward and covered their father’s nakedness. Their faces were turned the other way so that they would not see their father’s nakedness. When Noah awoke from his wine and found out what his youngest son had done to him, he said, ‘Cursed be Canaan! The lowest of slaves will he be to his brothers.’"
Why did Noah curse Canaan when it was Ham who saw him naked? Why was Noah so angry that Ham saw him naked? Some propose that Ham and/or Canaan actually did something to Noah in addition to seeing him naked. The passage mentions that Noah was angry when he found out “what his youngest son had done to him.” Homosexuality, rape, and humiliation are frequently mentioned as possibilities. One rabbinic teaching is that Ham or Canaan castrated his father. However, the text nowhere states what Ham did to Noah. Any theory of what occurred is speculation.
Another view arises out of comparison with Leviticus 20:11, "The man who lies with his father’s wife has uncovered his father’s nakedness..." With Leviticus 20:11 in mind, some propose that Ham had sex with Noah’s wife, and that was what brought the curse from Noah. However, this figurative understanding of "uncovering nakedness" fails to account for the fact that Shem and Japheth walked into the room backward and covered Noah with a garment. This does not make any sense if "uncovering nakedness" means "having sex with Noah’s wife." It definitely seems that Noah was lying naked—his nakedness uncovered.
Whatever took place between Ham and Noah, why did Noah curse Ham’s son Canaan, when Canaan is nowhere mentioned as having done anything? The Bible does not specifically answer this question. Ham was Noah’s youngest son, and Canaan was probably Ham’s youngest son (Genesis 10:6). The “youngest son” who mistreated Noah (Genesis 9:24) seems to be a reference to Ham, but another option is that it refers to Canaan, Noah’s youngest grandson. Calling a grandson a “son” is not uncommon in Scripture (cp. Ezra 5:1 and Zechariah 1:1). This would mean that Canaan was somehow involved in the sordid incident, and that is why Noah specifically mentions him in the curse (verse 25). Ham saw his father’s condition and did nothing about it except to tell his brothers. Reading between the lines, we assume that Ham’s son did more than see but participated somehow in his grandfather’s degradation.