In the mid-18th century, some scholars started a critical study of doublets (parallel accounts of the same incidents), inconsistencies, and changes in style and vocabulary in the Torah.[14] In 1780 Johann Eichhorn, building on the work of the French doctor and exegete Jean Astruc's "Conjectures" and others, formulated the "older documentary hypothesis": the idea that Genesis was composed by combining two identifiable sources, the Jehovist ("J"; also called the Yahwist) and the Elohist ("E").[16] These sources were subsequently found to run through the first four books of the Torah, and the number was later expanded to three when Wilhelm de Wette identified the Deuteronomist as an additional source found only in Deuteronomy ("D").[17] Later still the Elohist was split into Elohist and Priestly ("P") sources, increasing the number to four.[18]