Orality and Memory Hypothesis is a red herring

This is another post provoked by The Synoptic Problem: Four Views (Baker, 2016). The fourth view included in this introductory guide is the Orality and Memory Hypothesis. In presenting this option Rainer Riesner points out that orality and memory were an important feature of the first century context. In consequence, he suggests that we should think of the relationships between Mark, Luke and Matthew as always indirect rather than direct. When his theory is presented in diagram form (p. 107) there are multiple lines of connection between the sources (oral and written) used by Matthew, Mark and Luke but no lines of direct connection between them. In effect Riesner seems to suggest that Matthew, Luke and Mark were willing to use any number of other sources (written and oral) - just so long as it wasn't one of the other Synoptic Gospels. This is bizarre. Assuming that one of the Synoptic writers wrote after the other two, why would he specifically avoid using earlier texts from the textual tradition in which he was actually working? This seems to be the flip side of the usual 'all or nothing' mentality. Usually, scholars assume, for example, that if Matthew used Mark then he cannot also have used sources used by Mark. In this case, however, Riesner appears to assume that, if Matthew used Mark's sources, then he cannot also have used Mark! There is, in reality, no reason why Matthew should not have used Mark as well as Mark's sources. And this brings us back to the essential question. The first step towards solving the Synoptic Problem is to determine whether there is any direct borrowing between Mark, Luke and Matthew. Once this basic issue has been decided, then it makes sense to consider other factors, such as the role of orality and memory. First things first, however. There are high levels of agreement in order and specific wording between Mark, Luke and Matthew. Given that there are no good reasons to suggest that a later gospel writer would have specifically avoided direct copying from an earlier gospel writer, it is reasonable to expect that there is some degree of direct copying between them. The first question to answer, therefore is: who, regardless of whatever else might also have been going on, was directly copying from whom?