I'm currently reading through Francis Watson's new blockbuster Gospel Writing (Eerdmans 2013). He starts out the book with a discussion of how the affirmation of the fourfold canon (Matthew, Mark, Luke, and John) presented problems for Augustine and others who were trying to affirm the historical value of the books in light of disagreements among the authors. The interesting point thus far is that it is actually the theological convictions of early Christians that create the problems that their theological convictions then lead them to try to solve. In short, although affirmation of the fourfold canon was a theological conclusion of sorts, it was also an impetus for a line questioning that continues to today. He offers these interesting points in reference to Augustine's attempt at harmonizing the gospels in De consensu:
"But it is Augustine himself who endangers the canonical structure by exposing it to this kind of empirical thinking. . . . Reimarus is unthinkable without Augustine. Augustine not only makes it possible for Reimarus to argue that his ten contradictions within the gospel Easter narratives are destructive of Christian faith; he also makes it easy for him to do so" (43 - 44).
In conversation with Dr. Le Donne, I've often stated that I think historical Jesus research really starts with precisely this work by Augustine, so I'm happy to see Watson arguing something that is at least sympathetic with that notion. I'm reading this book as I prepare for a panel review of it at the British New Testament Conference later this month. I have lots more reading to do and I'll be anxious to hear Watson himself say more on this topic.