Devarim 34:5 records that Moshe died, but the Torah has another eight verses. This raises the question recorded in the Talmud (Baba Bathra 15a), how could Moshe have written the remainder of the Torah, the last eight sentences, if he was dead? Rabbi Yehuda, or maybe Rabbi Nehemiah, answers that really Yehoshua wrote the last eight sentences of the Torah. Rabbi Shimon disputes this since according to Rabbi Yehuda the Torah would have been incomplete when Moshe handed the Torah over to the priests (in Devarim 31:25). Thus, Rabbi Shimon claims that Moshe wrote the last eight sentences with tears since he was writing about his death. The problem with the second approach is that 34:5 is written in the past, but if Moshe wrote about his death it should have been phrased in the future.
Heschel (1965, pp. 381-391) argues that the two answers represent two different approaches to understanding the Torah. Rabbi Shimon follow the school of Rabbi Akiva that the whole Torah was given on Mount Sinai, while Rabbi Yehuda or Rabbi Nehemiah follow the school of Rabbi Yishmael that only the main principles were given on Mount Sinai.
While the Talmud discusses whether Moshe or Yehoshua wrote the last eight sentences of the Torah, 34:5-12, Ibn Ezra (1089-1164, on 34:1, also see comments on 34:6) argues that all of chapter 34 was written by Yehoshua. Ibn Ezra’s reason in that 34:1 records that Moshe went up on Mount Nevo, and there is no mention that Moshe came down again. How could Moshe have written even the beginning of chapter 34 if he was unable to hand it over to anybody? One possibility is that Moshe wrote the beginning of chapter 34 before he went up the mountain, as a future prophecy. Yet, 34:1 records that Moshe went up, in the past, and not that Moshe will go up, as would have been needed if chapter 34 was written as a future prophecy. A second possibility is that somebody went up with Moshe but this also seems to be ruled out by 34:6 that nobody knew where Moshe was buried. It seems unlikely that somebody (Yehoshua?) went up with Moshe and then came down before Moshe died.
Pinchas Horowitz (1730-1805, Panim Yafot) suggests that really Moshe went up twice, and 34:1 only records the first time. However, this also is difficult since there is no indication of this double climb in the Torah.
Chatam Sofer, (1762-1839, a student of Pinchas Horowitz, in Torat Moshe, Chatam Sofer al haTorah) suggests but then rejects the possibility that Moshe wrote 34:1-4 on the mountain, and left it for the Jewish people to find. He rejects this idea since 31:26 records that Moshe gave the Torah to the Levites, and it seems that he accepted Ibn Ezra’s explanation.
David Hoffman (1961, p. 573) deduces from the Ramban's comments on 31:24 that the Ramban agreed to the Ibn Ezra's opinion that Yehoshua wrote all of chapter 34. Heschel (1965, p. 392) suggests that Tosafot in Megillah 21b Tana also follows Ibn Ezra’s explanation. In addition, Yehuda Nachshoni (1987, p. 843), writes that Ibn Ezra’s approach is basically the approach in the Talmud that Yehoshua wrote the last 8 sentences since what is the difference whether Yehoshua wrote the last 8 or the last 12 sentences?
This comment by Ibn Ezra on 34:1 shows that he did not believe that Moshe wrote the whole Torah, and he has other comments which seem to indicate that there were other verses or parts of verses that he also thought were written after Moshe died. Most famously, on Devarim 1:2, Ibn Ezra writes “that if one knows the meaning of the twelve, Bereshit 12:6, Bereshit 22:14, Devarim 3:11 and 31:22, then one will know the truth.” It is likely that the phrase “the meaning of the twelve” is referring to the twelve verses in chapter 34, but this cannot be known conclusively, see Luzzatto’s comments on Devarim 1:1. However, if it true, then this implies that Ibn Ezra thinks that the other verses that he mentions were similar to what he explained on chapter 34, which means that just as he thinks that chapter 34 was added to the Torah after Moshe died, so too these verses or phrases were added to the Torah after Moshe died. Furthermore, maybe one could add that just as Ibn Ezra believes that Yehoshua added chapter 34 to the Torah, so too he thinks that Yehoshua added the other verses or phrases to the Torah.
Marc Shapiro (1993, p. 202) lists 15 Rabbi’s from the 13th to the 20th centuries who understood Ibn Ezra to be saying that he considered the five cases he mentioned in his comments on Devarim 1:2 to have been included in the Torah after the time of the Moshe, which would be the meaning of the phrase “know the truth.” Simon (2013, pp. 407-464) has an extensive discussion on how people understood Ibn Ezra’s comments and he seems to conclude that the best understanding of Ibn Ezra’s words is that Ibn Ezra believed that the phrases or verses which he mentioned in his comments on Devarim 1:2 were added after Moshe. Simon also points out that in addition to the verses mentioned in Ibn Ezra’s comments on Devarim 1:2 and not including his explicit comments on Devarim 34:1,6, Ibn Ezra also hinted in his comments on Bereshit 13:7 (which is similar to Bereshit 12:6), Bemidbar 13:24, and Devarim 11:30, that the verses were either not written by Moshe or were written by Moshe as a prophecy of the future. Simon also explains that Ibn Ezra refers to his comment on Devarim 1:2 in his comments on Bereshit 22:14.
Michael Friedlander (1963/64, pp. 60-67) argues that Ibn Ezra only believed that chapter 34 was not written by Moshe. Friedlander disputes the idea that in his comments on Devarim 1:2, Ibn Ezra was implying that the particular verses were not written by Moshe. Friedlander argues that had Ibn Ezra had that opinion he would have written it clearly as he did on 34:1. Furthermore, Friedlander claims that when Ibn Ezra wrote on Devarim 1:2, “you shall know the truth” this refers “to some philosophic theory which Ibn Ezra believed to be hidden in the Biblical text.” Friedlander further suggests that as three of the verses quoted by Ibn Ezra refer to geography and archeology, Ibn Ezra was puzzled why they were included in the Torah since he did not think these were important subjects. Finally, Friedlander questions whether we really know which are the first two verses referred to by Ibn Ezra in his comments on Devarim 1:2, and again he speculates that they were part of the list since Ibn Ezra could not understand why they were included in the Torah.
There are two other comments of the Ibn Ezra that are pertinent to understanding his view of whether Moshe wrote the entire Torah. One, on Bereshit 36:31, Ibn Ezra quotes an opinion of somebody named Yitzhaki who suggested that the list of kings of Edom was included in the Torah in the times of Yehoshafat, 9th century BCE, many years after Moshe. Ibn Ezra sharply rebukes this opinion and states that Yitzhaki’s book should be burnt for this suggestion. Two, on Bemidbar 21:1, Ibn Ezra quotes in the name of many, that the verses which record the battle with the King of Arad happened in the time of Yehoshua and thus Yehoshua and not Moshe would have written Bemidbar 21:1-3. He rejects this possibility but not in as critical manner as he does with regards to Yitzhaki.
Why did Ibn Ezra castigate Yitzhaki for suggesting that Moshe did not write Bereshit 36:31-43 if he believed that there were other verses in the Torah not written by Moshe?
Menachem Kasher (1992, Vol. 19, p. 378) writes that after Ibn Ezra said that the book of Yitzhaki is to be burnt, then there is no way that Ibn Ezra believed that any part of the Torah was written after Moshe. Thus, he claims that any comments that give the opposite impression were not written by Ibn Ezra but inserted later. This idea was already suggested by Shmuel Zarza (Mekor Hayyim, supercommentary on Ibn Ezra, 14th century), but it is a very difficult argument without any other proof that these comments were not from Ibn Ezra.
Joseph ben Eliezer Bonfils (14th century, supercommentary on Ibn Ezra, Tzafenat Pane’ah) argues that Ibn Ezra distinguishes between adding words and sections. According to this, Ibn Ezra was willing to allow words to be added to the Torah, but not a complete section like the list of kings of Edom. The problem is that Ibn Ezra claims that Yehoshua wrote all of chapter 34 and this certainly was a complete section.
Friedlander (pp. 221-223) quotes R. Shemtob ben Joseph Shaprut of Toledo (2nd half of the 14th century) who suggested that all the verses mentioned by Ibn Ezra were additions made by Yehoshua. According to this, Ibn Ezra accepted that only Yehoshua could add to the Torah. Presumably the reason would be that not only was Yehoshua a prophet, as recognized in the Torah, Bemidbar 27:18-21 and Devarim 31:23, but also he was the student of Moshe. (Also, on Devarim 18:15, Ibn Ezra suggests that Yehoshua was to be the prophet who was comparable to Moshe.) Ibn Ezra then was critical of Yitzhaki since Yitzhaki’s explanation was that the list of kings of Edom was added to the Torah after the time of Moshe and Yehoshua.
Uriel Simon offers two other explanations. One, (1982, p. 677) Ibn Ezra accepted additions to the Torah only when he thought that the particular verses could not have been written by Moshe, but Ibn Ezra accepted that Moshe could write about the future through prophecy. For example with regards to chapter 34, as explained above, Ibn Ezra thought Moshe could not possibly have written the verses. However, with regards to the list of kings of Edom in Bereshit 36, Moshe could have known this through prophecy, and thus Ibn Ezra rejected Yitzhaki’s approach. (Ibn Ezra in his commentary on Bereshit 36:31 also explains that the kings of Edom were before the time of Moshe.)
Two, Simon (1993, pp. 299-317) suggests that Ibn Ezra thought Yitzhaki was a pretentious but unqualified commentator, and thus "Ibn Ezra would not allow an unqualified commentator to do what he himself did." I doubt this suggestions since it can only explain why Ibn Ezra rejected and ridiculed Yitzhaki’s approach, but not why he called for the book to be burnt.
Even if Ibn Ezra only believed that Yehoshua wrote chapter 34, this means that he did not accept the Rambam’s eighth principle of faith that one must believe that the Torah we have today is exactly what was given to Moshe. (The list of principles is in the Rambam’s Introduction to Helek, chapter eleven in Sanhedrin based on the Talmud, but chapter ten based on Mishnah. The complete list is quoted in English in Twersky, 1972, pp. 401-423. Also see Mishnah Torah, Laws of Repentance, 3:8.) The Rambam was born in 1135 (1138?) when Ibn Ezra was forty six, which means that Ibn Ezra probably never knew or even heard of the Rambam, even though both were from Spain (Ibn Ezra left Spain in 1140), but the Rambam could have known about the Ibn Ezra. Could it be that the Rambam’s eighth principle of faith was because he was attempting to refute Ibn Ezra’s opinion?
How did the Ibn Ezra understand the Talmud that was the basis for the Rambam’s eighth principle of faith? The Talmud (Sanhedrin 99a) states that a person who accepts that all of the Torah is from G-d except for one verse which Moshe wrote on his own, is guilty of “despising the word of G-d” (Bemidbar 15:31) for which the punishment is karet.
This statement in the Talmud is problematic not just for Ibn Ezra but also for the opinion in the Talmud that Yehoshua wrote the last eight verses of the Torah. Heschel (1965, pp. 91-93, 381-5) argues that the difficulty is because one is confusing the school of R. Akiva and the school of R. Yishmael. He argues that it is the opinion of R. Akiva’s school that one cannot say that one verse is from Moshe or anybody else, and this is the same opinion that Moshe wrote the last eight sentences of the Torah. However, the school of R. Yishmael understands that the sin of “despising the word of G-d” refers to committing idolatry, as one has despised the first commandment of the Decalogue which was said by G-d, and thus this school can accept that the last eight verses in the Torah were written by Yehoshua. Accordingly, maybe Ibn Ezra was following the school of R. Yishmael, while Rambam followed the school of R. Akiva.
Simon (2013, p. 429) quotes Joseph ben Eliezer Bonfils (Tzafenat Pane’ah) who argued that the opinion in Sanhedrin 99a that a person cannot state that any verse was written by Moshe on his own was only referring to laws and not to narrative, while all of the verses where Ibn Ezra might have suggested that Moshe did not write them are narrative. R. Menachem Kasher (Torah Shelemah, 1982, Vol. 19, p. 378) quotes this opinion and completely rejects it.
Dr. Shnayer Z. Leiman (contemporary, on tape titled “Torah min ha-Shamayim”, available at www.torahtapes.org, also see Leiman 2003, pp. 21,22) discusses two other ways (not in accordance with the Rambam) to understand the view in the Talmud that one cannot say that a verse in the Torah is not from G-d but Moshe wrote it on his own. One, the Talmud is not rejecting the view that later prophets could have added to the Torah since that is not despising the word of G-d because prophecy is also the word of G-d. Thus, Ibn Ezra on 34:1 writes that Yehoshua wrote chapter 34 with prophecy. A second possibility is that the Talmud only forbids one to say that Moshe wrote the Torah on his own, but that does not preclude the possibility that some verses were added after the time of Moshe.
In conclusion, for sure Ibn Ezra believed that Moshe did not write chapter 34 of the book of Devarim, and it is highly likely that there are a few other verses or phrases in the Torah which he also thought were added after Moshe’s life. It is possible that he thought that all of these additions were done by Yehoshua, but this cannot be known definitely. Finally, most likely he did not view this belief as being a contradiction to the Talmud in Sanhedrin 99a possibly for one of the four reasons mentioned above.