It was Julius Wellhausen, however, who would alter the course of source studies for the next century, by arguing in his Prolegomena zur Geschichte Israels (originally entitled just Geschichte Israels), that each of the sources were born from various stages and geographical distinctives in the history of Israelite religion. He argued that J was written in 950 BCE in the Southern Kingdom of Judah, that E was written in 850 BCE in the Northern Kingdom of Israel, that D was written around 600 BCE during Josiah's reform, and that P was written by captive priests in Babylon during the exile. They all had individual redactors that combined them along various stages (JE, JED), and then were ultimately combined into the larger books of the Pentateuch we have today (JEDP).
Wellhausen's theory was based on a Hegelian understanding of religion that saw history as developing toward enlightenment (in Hegel's view toward oneness with God in terms of his monism). Hence, a more primitive language and understanding of God, largely in terms of anthropomorphic and immanent concepts within the framework of polytheism and henotheism, were less developed, and therefore, earlier than later stages of the religion, where God is transcendent within a monotheistic understanding of deity.
Hence, as Whybray noted, "Wellhausen was a historian, concerned not only with a literary question but with the history of Israel and more particularly with the history of its religion. He saw the sources or 'strata' (Schichten) of the Pentateuch as reflecting different stages of this historical development, especially of the development of the cult.[1] In fact, his work was originally meant to be a two volume treatise on the history of Israel (i.e., the Jewish religion), but the second volume never transpired.
Although some scholars object to noting Wellhausen's Hegelian assumptions, it is important to do precisely that because Wellhausen received his framework from it. If his assumptions were wrong (i.e., that religion does not necessarily develop as he has reconstructed it, and the language used cannot function as evidence of a more or lesser primitive development) then his work largely falls apart. The sources remain, but the data may have an alternate interpretation that is more plausible. We'll discuss further developments of Wellhausen's theory next time, and then look at some of the alternatives that have been proposed in the past and present.