Proponents of the various versions of the Documentary Hypothesis believe there must be 4 or more authors of the Pentateuch for several reasons, but the three most common are:

1. Some texts in Genesis refer to God as Yahweh, whereas others call him Elohim. A single author would not use two different names for God.
2. The books of the Pentateuch contain duplicate stories and repetitions. A single author would not repeat himself in this manner, thus multiple authors must be behind the text.
3. The language and style of the Pentateuchal documents vary. There are genealogies, censuses, narratives, and legislation. A single author would not use so many writing styles.

How do critics of the Documentary Hypothesis respond?

1. The names of Yahweh and Elohim are often used contextually because they represent different aspects of God. Yahweh is the covenant name of God, which emphasizes his special relationship to Israel. Elohim speaks of God’s universal rule over all the earth. In addition, it was very common in the ancient near east for writers to use multiple names for a single god.
2. Duane Garrett explains, “The use of doublets and repetition as evidence for multiple documents in Genesis is perhaps of all the arguments the most persuasive for the modern student, while in fact being the most spurious and abused piece of evidence. . . . The assumption appears reasonable, but it is altogether a fallacy. It is an entirely modern reading of the text and ignores ancient rhetorical concepts. In an ancient text, there is no stronger indication that only a single document is present than parallel accounts. Doublets, that is, two separate stories that closely parallel one another, are the very stuff of ancient narrative. They are what the discriminating audience sought in a story.” Again, we know from other ancient near east documents that parallelism and repetition was an important part of the story-telling process, so a single author would frequently make use of this device.
3. A single author may change literary styles within a single document. He may have different purposes for different portions of the document. Matt Slick reminds us, “A technical work is different from a narrative or historical piece.  The Pentateuch has components of all of these. Therefore, different styles are expected.”