Oral gospel traditions called the M source for Matthew and the L source for Luke, which may have been a mix of written and oral material (see Two-source hypothesis). Most scholars believe that the author of John's gospel used oral and written sources different from those available to the Synoptic authors – a "signs" source, a "revelatory discourse" source, and others – although there are indications that a later editor of this gospel may have used Mark and Luke. Oral transmission may also be seen as a different approach to understanding the Synoptic Gospels in New Testament scholarship. Current theories attempt to link
Synoptic Gospels eighteenth century, when Johann Jakob Griesbach published in 1776 a "synopsis" of the synoptic gospels. Instead of harmonizing them, he displayed their texts side by side, making both similarities and divergences apparent. Griesbach, noticing the special place of Mark in the synopsis, hypothesized Marcan posteriority and advanced (as Henry Owen had a few years earlier) the two-gospel hypothesis (Matthew–Luke). In the nineteenth century, researchers applied the tools of literary criticism to the synoptic problem in earnest, especially in German scholarship. Early work revolved around a hypothetical proto-gospel ("Ur-Gospel"), possibly in Aramaic, underlying the synoptics. From this line of inquiry, however,