Despite the continuing debate between Matthean and Markan priorists, some form of the widely-accepted Two-Source Hypothesis seems necessary for a proper understanding of the synoptic relationships. The Two-Source Hypothesis as generally conceived, however, cannot cover the evidence of dependence and interdependence found in the Gospels of Matthew, Mark and Luke. The same must be said for the theory of Matthean priority.
Both Markan and Matthean priorists are guilty of trying to solve the synoptic problem by over reliance on evidence for the interdependence of the Synoptic Gospels. These theorists’ basic error stems from their failure to recognize the necessity of positing the existence of a document other than Q, a document that is not completely present in any of the canonical Gospels. The interdependence of the Synoptic Gospels is a fact from which no theory of origins can escape, but the evidence of dependence on an additional document no longer extant, yet known to each of the synoptic writers, demands an adequate literary explanation.
Very few twentieth-century synoptic theorists can be said to have wrestled seriously with the question of whether a Mark-like, extra-canonical authority may not be necessary to explain unsolved problems of synoptic relationships. Instead, the tendency has been to abandon all hope of finding a literary solution.
-  Cf. Otto A. Piper, “The Origin of the Gospel Pattern,” JBL 78 (1959): 115. ↩