In fundamentalist traditions of faith it is taken for granted that Moses was the author of the Torah. The Rambam even declared that Moses was the sole author of the Torah who wrote it down as directly dictated to him letter for letter by God. This bold assertion by the Rambam doesn't hold up to scrutiny though and previous to the Rambam the Talmud declared that the authorship of Moses doesn't apply to the last eight verses of Deuteronomy which describe in detail the death of Moses (b. Baba Batra 15a). Later, Rabbis would also exclude other verses from being penned by Moses such as Ibn Ezra (1089-1164) who wrote in regard to Genesis 12:6:
“and the Canaanites were then in the land,” “It would seem that the Canaanites took the land of Canaan from a different group, but if this is not correct, then there is a secret here, and the wise will remain silent.”… “If you understand the secret of the twelve—as well as ‘and Moses wrote’ (Deut. 31:22), ‘and the Canaanites were then in the land’ (Gen. 12:6), ‘on the mountain God will appear’ (Gen. 22:14), ‘here is his iron bed’ (Deut. 3:11) – you will recognize the truth.”
The Tzafenat Pa’aneach—a commentary on Ibn Ezra by R. Joseph ben Eliezer Bonfils (14th cent.), explains the Ibn Ezra’s secret:
“…the meaning is this: How could [the Torah] use the word “then” in this context, which implies that [the Canaanites were there] then but that they are not there now. But didn’t Moses write the Torah and in his time the Canaanites ruled the land? It makes no sense for Moses to write “then.” Reason dictates that the word “then” could only have been written at a time when the Canaanites were not occupying the land, and we know that the Canaanites were not removed from the land until after Moses’ death during the conquest of Joshua. According to this, Moses did not write this word here, rather Joshua or one of the later prophets wrote it…”
So what is going on here? The commentary is stating that the word "then" in the Torah verse (Gen. 12:6) does not seem like a grammatical style being used by a present witness (Moses) experiencing a present reality (Caananites in the Land), rather the verse it apparently a later author writing about a past experience which would undoubtedly make Moses not the author of this verse.
Other Rabbis, such as Radak (1160-1235), Hizkuni (13th cent.), and R. Judah the Pious (1140-1217) also interpreted many other verses in the Torah as not being penned by Moses and they attributed most of the verses to the editing Scribes of the Great Assembly.
The Torah never actually states that it was written by Moses. There are a few verses sporadically taken out of context which state that Moses wrote down some words of the Law and also read these words to the community of Israel. For example, “And Moses wrote all the words of YHVH” (Exodus 24:4). “And he took the book of the covenant, and read in the audience of the people” (Exodus 24:7). “And YHVH said to Moses, ‘Write these words; in accordance with these words I have made a covenant with you and with Israel’” (Exodus 34:27). In light of these verses it would seem rather bizarre to assert that these early readings of a Law in Exodus should represent a reading and writing of the whole Torah through to Deuteronomy. Some Rabbis assert that this is exactly what is being implied and they point out that Moses accomplished this feat via prophecy. Therefore, according to those who want to maintain a fundamentalist view of Mosaic authorship for the entire Torah, we have to have faith that Moses wrote the whole Torah on Sinai by dictation from God who gave Moses prophetic insight into every detail which was impossible for him to know. Is this a rational position to affirm or should we consider that Moses did not receive the whole Torah on Sinai nor did the words he write or the Laws he read in Exodus represent an exhaustive and complete rendition of the Torah as we have it today? The Torah is rather a progressive revelation and process of writing that transpired over time.
Other assertions used to support Mosaic authorship is the argument that throughout the Tanakh the Torah is referred to as the "Books of Moses," indicating that Mosaic authorship has always been a given. However the term "Books of Moses," and/or "Torah of Moses," no more demonstrates authorship than the title "Book of Job" indicates authorship by Job; nor does the "Book of Kings" indicate that this work was written by Kings. The "Books of Moses" indicate a collection of books wherein Moses is depicted as a primary character in the narrative.
Further, we must consider that the Torah's accounts of Moses are not written as a first person account as we would expect rather Moses is referred to in the third-person from start to finish. Even the great speck of Moses to the Israelites in the opening of Deuteronomy is recorded as: "These are the words that Moses addressed to all the people of Israel." The wording of the previous verses we refered to: Exodus 24:4, "And Moses wrote…" and the wording in Exodus 24:7, "And he took…" are written as a story about Moses in the third-person. Someone is writing about Moses- Moses is not writing about himself.
We have to also consider that there are persons, places and things mentioned in the Torah that Moses could not have known anything about. For example, the Edomite Kings listed in Genesis 36 didn't exist until after the death of Moses. There are things written about the Land of Israel and Moses never entered the Land of Israel to obtain first-hand information. The Torah talks about Philistines but the Philistines didn't exist during the time of Moses rather they appeared on the coasts of Canaan around 1200 BCE.
Other anomalies that point to a later composition of the Torah (specifically Deuteronomy) is the apparent statement in Deuteronomy 34 where the writer states:
"There never arose another prophet in Israel like Moses."
How could Moses or any other contemporaneous author write that no other prophet arose in Israel like Moses when the author is supposed to be writing at a time before they were ever in Israel?
One final observation must also be considered from Numbers 12:3:
“Now Moses was a very humble man, more so than any other man on earth…”
If Moses is writing about himself in the third-person testifying to his own humility then Moses wasn't very humble at all! This verse solidifies that obvious- the Torah is "about" Moses it is not "by" Moses.
It is imperative that the Torah be read in its correct context and not in an imaginative setting of fantastic impossibility. Nothing of value can be drawn from a text when the interpreter is ignorant of the basic origin and composition of the text.