Four-document hypothesis based on Two-source hypothesis
The four-document hypothesis or four-source hypothesis is an explanation for the relationship between the three Gospels of Matthew, Mark, and Luke. It posits that there were at least four sources to the Gospel of Matthew and the Gospel of Luke: the Gospel of Mark and three lost sources (Q, M, and L). It was proposed by B. H. Streeter in 1925, who refined the two-source hypothesis into a four-source hypothesis.