AKA Documentary Hypothesis
A theory stating that the Torah, the five books of Moses, was compiled over time, primarily from the works of four people (or more likely, groups of people) working off of oral tradition, rather than being the work of God or even necessarily divinely inspired. This provides a very simple explanation for the many contradicions found in the Torah, as each piece of the contradiction can usually be attributed to a different author. Perhaps both were left in because no one could be sure if one was more correct than the other, or perhaps it was simple editorial oversight. Either way, it's a pretty cool theory.
The four people/groups have different writing styles, identifiable throughout the Torah and have been given the highly inventive yet functional names J, E, P, and D. Some also name an R, the Redactor, who editted the separate works and put them all together, forming the Torah we enjoy today.
The four others, in a nutshell:
- J, the Jahwist, refers to God using the Tetragrammaton, or YHWH. J tends anthropomorphise God.
- E, the Elohist, refers to God as "Elohim". E deals more with prophecy -- instead of anthropomorphizing God, in E's writing God speaks in dreams.
- P, the priestly, deals with many of the technical aspects of Judaism -- what obligations must be fulfilled and such. That makes P the primary author of Leviticus, which deals primarily with Judaism's legalese, so to speak. P also deals with the priesthood and genealogies.
- D, the Deuteronomist, is the author of Deuteronomy in its near-entirety. It is D's work that King Josiah supposedly found in 622 BCE. D takes a moralistic approach to Judaism, and tends to be much less devoted to its technical aspects than P.
Note: J and E are thought to be the earlier of the four sources, and at some point their works were likely merged. Because of this, it's sometimes hard to tell them apart.