Ibn Ezra on Gen 12:6

And Abram passed through the land unto the place of Sichem, unto the plain of Moreh. And the Canaanite was then in the land. Gen 12:6

Among the many delightful things I learned from Marc Shapiro's wonderful book was that before Moses ben Maimon emerged from his study* with his list of ikkarim (principles) Jews were very much deivided about what constituted heresy. Some Jews thought God might have corpreal qualities. Others were of the opinion that our Torah might not a letter-for-letter match with the Torah Moshe received at Sinai

One of these men was the Ibn Ezra**, an authentic and legitimate sage with a commentary that appears in the Mikraot Gedolot (The big book of authentic and legitimate bible commentaries.) On Gen 12:6 he says: “it is possible that the Canaanites seized the land of Canaan from some other tribe at that time (i.e. then, but not prior to this). Should this interpretation be incorrect, then this text contains a great secret and the wise man will remain silent.”

What is the Ibn Ezra's secret? To find it, we must unpack his comment:

...it is possible that the Canaanites seized the land of Canaan from some other tribe at that time.
The land the Torah calls Canaan was given, by Noah, to Shem. Canaan is a decendant of Ham, not Shem. Rashi tells us that Canaan conquered the land from Shem before Abraham arrived, and this is why the verse tells us "And the Canaanite was then in the land." The Ibn Ezra concedes this view might be right, and continues:

Should this interpretation be incorrect, then this text contains a great secret and the wise man will remain silent
What's the secret? Well, if the Cannaite had not yet conquered the land from Shem (as suggested by the appearence of MalkiTzedek later in the story) the Torah's statement is very strange indeed. Because, when the Torah was giventhe Canaanites were still in the land. The word "then", however, implies they are no longer in the land, suggesting that the last part of Gen 12:6 was added after Moshe.

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* I'm being a bit facitious here. Initially, the Rambam's books were burned. His views didn't win the day until August 8, 1321 @ 9:29 am.

** Others who disagreed with the idea that the Torah we have is a letter-for-letter match with the Torah Moshe received include:

Talmudic and midrashic sources They list between 7 and 18 tikunei sofrim (scribal corrections) and 5 ittur sofrim (scribal omissions) Also, the Talmud quotes psukim that do not appear in that form in our Torah. The most famous example is in Sanhedrin 4b where Rabbi Yshmael derives a law from the spelling of the word totafos. However, in all known copies of the Bible the word is not spelled the way Rabbi Yishmael has it. There are about 20 example of this, and regarding this phenomenon Tosfot says Hashas shelonu cholek in haseforim shelonu (our gemrah disagrees with our books) Additionally, the Talmud tells us that three scrolls containing varient readings were once found in the Temple courtyard. The differences were resolved, in each instance, after the majority. It's unlikely that the result, in every instance, matched the original revelation.

Rav Yosef in Kiddushin 30a says: "They are expert in matters of defective and plene spelling; we are not expert." This refers to a system of using consonants to indicate certain vowels. Rav Yosef is saying we've forgotten the system.

Avot d'rabi Nathan and the Midrash Raba who both suggest Ezra, not Moshe, wrote the dotted words.

Some old Rashi manuscripts say outright that he believed that the Sages revered the writing of the Torah in some places

We also have a system in which marginal notes indicate that certain words are to be read differently than they are spelled in the text, called "kere and ketiv." Regarding this the Radak wrote: "It appears that these words are here because during the first Exile, books were misplaced and lost and scholars died; when the Great Assembly restored the Torah they found conflicting information in manuscripts and went according to the majority. "

In his introduction to Masoret Seyag LaTorah, the Ramah wrote: "If we seek to rely on the proofread scrolls in our possession, they are also in great disaccord. Were it not for the Masorah which serves as a fence around the Torah, almost no one would find his way in the controversies between the scrolls. Even the Masorah is not free from dispute, and there are several instances disputed [among the Masorah manuscripts], but not as many as among the scrolls. If a man wishes to write a halakhically "kosher" scroll, he will stumble on the plene and defective spellings and grope like a blind man through a fog of controversy; he will not succeed. Even if he seeks the aid of someone knowledgeable, he will not find such a one. "

R. Yom Tov Lipman Milhausen, in Tikkun Sefer Torah wrote: "Because of our many sins, the Torah has been forgotten and we can not find a kosher Torah scroll; the scribes are ignoramuses and the scholars pay no attention in this matter. Therefore I have toiled to find a Torah scroll with the proper letters, open and closed passages, but I have found none, not to mention a scroll which is accurate as to the plene and defective spellings, a subject completely lost to our entire generation."