The majority of the Bible scholars and students today, within both Christianity and Judaism, will without a doubt, identify Moses as the author of the Torah, the first five books of the Bible. Yet, nowhere within the text of the Torah is the author of the Torah identified. Not only is it possible that different authors wrote different portions of the Torah, but it is possible that different authors wrote about the same account.
And Moses was an hundred and twenty years old when he died: his eye was not dim, nor his natural force abated. And the children of Israel wept for Moses in the plains of Moab thirty days: so the days of weeping and mourning for Moses were ended. And Joshua the son of Nun was full of the spirit of wisdom; for Moses had laid his hands upon him: and the children of Israel hearkened unto him, and did as the LORD commanded Moses. And there arose not a prophet since in Israel like unto Moses, whom the LORD knew face to face, In all the signs and the wonders, which the LORD sent him to do in the land of Egypt to Pharaoh, and to all his servants, and to all his land, And in all that mighty hand, and in all the great terror which Moses shewed in the sight of all Israel. (Deuteronomy 34:7-12, KJV)
It is obvious that Moses did not write this account; therefore we know that this portion was written by someone else. Is it not then possible that other portions may have been written by someone other than Moses?
And these are the kings that reigned in the land of Edom, before there reigned any king over the children of Israel. (Genesis 36:31, KJV)
During the lifetime of Moses no king resided over Israel. The author of this passage is writing about the kings of Israel from the viewpoint that they are facts of history. The author lived during, or after, the time of the kings of Israel.
And Rachel died, and was buried in the way to Ephrath, which is Bethlehem. (Genesis 35:19, KJV)
As the city of Ephrath was not known as "Bethlehem" until long after Moses, the three words “which is Bethlehem” (hee beyt lehem in Hebrew) were obviously written by someone other than Moses. Granted, we are only speaking of three words, but if three words from the Torah can be written by someone other than Moses, then why not six words or one hundred words?
When the people saw the thunder and lightning and heard the trumpet and saw the mountain in smoke, they trembled with fear. They stayed at a distance (Exodus 20:18, NASB)
Then Moses led the people out of the camp to meet with God, and they stood at the foot of the mountain. Mount Sinai was covered with smoke, because the LORD descended on it in fire. The smoke billowed up from it like smoke from a furnace, the whole mountain trembled violently (Exodus 19:17-18, NASB)
In the first account Israel sees the thunder and lightning and stays at a distance from the mountain. But, in the second account they go up to the mountain and see the smoke and fire. It appears that while two different authors wrote these two accounts they were combined into one story by one known as a redactor. This person took the various stories known at the time and attempted to place them all into one story. For this reason we see many of the same stories repeated at different times. While it is usually understood that these are two different stories occurring at two different times, they may be one story written by two different authors and combined into one story by the redactor.
And Abram (Abraham) said to the king of Sodom, "I lifted up my hand to Yahweh, El Elyon, possessor of heaven and earth. (Genesis 14:22, NASB)
And I appeared to Abraham, to Isaac and to Jacob as El Shaddai, and my name Yahweh I did not make known to them. (Exodus 6:3, NASB)
In the Genesis passage Abraham invokes the name Yahweh but according to the Exodus passage God did not reveal his name Yahweh to Abraham.
The Lord your God who goes before you on your way, to seek out a place for you to encamp, in fire by night and cloud by day, to show you the way in which you should go. (Deuteronomy 1:33, NASB)
Then he said, "Please do not leave us, inasmuch as you [Hobab] know where we should camp in the wilderness, and you will be as eyes for us. (Numbers 10:31, NASB)
In the Deuteronomy passage Moses tells the people that God will be their guide through the wilderness showing them which way to go an where to camp. But, in the Numbers passage Moses beseeches his father-in-law Hobab to go with them so that he can show them where to go and where to camp in the wilderness because he is familiar with the area.
Jethro, the priest of Midian, Moses' father-in-law, heard of all that God had done for Moses and for Israel his people, how the LORD had brought Israel out of Egypt. (Exodus 18:1, RSV)
And Moses said to Hobab the son of Reuel the Midianite, Moses' father-in-law, "We are setting out for the place of which the LORD said, `I will give it to you'; come with us, and we will do you good; for the LORD has promised good to Israel." (Numbers 10:29, RSV)
In Exodus 18, Moses’ father in law is called Jethro, while in Numbers 10 he is called Hobab.
We all speak and write differently and the styles of writing can be compared to determine the authors of different texts. As an example from English, one might say "I talked to mom," while another person might say "I spoke to my mother." We can easily see that these two phrases are from two different people.
We frequently these same variations in writing style within the text of the Torah. For instance, in Numbers 21:16 we readאמר יהוה למשה (amar yhwh l'mosheh) which means "Yahweh said to Moses." But in Exodus 4:30 we find the phraseדבר יהוה אל משה (diber yhwh el mosheh) which means "Yahweh spoke unto Moses." These differences in writing style are found throughout the text and in fact, we can even see the writing of one person throughout the text that is intermixed with the styles of writing from another person, a result of the redactor splicing together separate accounts into one.