The Q biblioblogging weekend is continuing apace. For whoever is doing the next Biblical Studies Carnival, here is a quick guide to the posts so far:
The Difference Makes Q (James McGrath)
Does the Difference Make Q (Mark Goodacre)
Spoiling Christmas vs Spoiling Q (James McGrath)
Christmas Still Looks Good, Q Not so Much (Rick Sumner)
Can Matthew Count to Fourteen? (Stephen Carlson)
There's no Q in Christmas (Doug Chaplin)
I don't have a lot to say in response to James's second post that I have not already said in The Case Against Q (54-9) or to add to what Rick, Stephen and Doug say in their excellent responses above. As I mentioned in my previous post, James's argument is a form of the classic argument from Luke's lack of M material. The key thing that James is trying to stress is that Matthew's and Luke's Birth and Infancy narratives are "incompatible". It is an argument that is only convincing if one thinks that no evangelist would deliberately contradict the work of a predecessor. But we know that that is not the case given Luke's departures from Mark's narrative, with similar "incompatible" elements.
When it comes to the details of the Birth and Infancy Narratives, I would like to make a couple of additional comments. First, one of the examples James provides of an "incompatible" detail is Luke's dating of the birth of Jesus. He says that "Matthew places Jesus' birth before the death of Herod in 4 BCE, Luke connects it with the census under Quirinius in 6 CE". But the disagreement over dates is no argument for Luke's independence from Matthew. Luke dates the birth of John in the time of Herod the Great (Luke 1.5) so unless we are to imagine Elizabeth having a ten year pregnancy, Luke's dating of the birth of Jesus is also "incompatible" with what he has previously told us.
Second, while we can only speculate as to why Luke prefers his own genealogy to Matthew's, my own guess would be that he prefers it for Christological reasons. Isaiah 11.1 speaks of a future ruler who will come up from the "stump of Jesse". The image here is of the great Davidic tree as having been cut down, as Judah goes into exile, and the monarchy is at an end. It is now a stump. But a shoot will rise from that stump, and there will be a restoration in which the king will be of David's line, but not descended from the line of all those kings who came after him, whose disobedience led to exile. Matthew's genealogy traces Jesus' lineage through all those kings who, in Luke's mind, are a felled tree. For Luke, Jesus' Davidic heritage is expressed in the genealogy in bypassing those kings, and tracing his lineage through Nathan rather than Solomon. Luke's genealogy is of a messiah who emerges from the stump of Jesse. If one is in any doubt about how important Isaiah 11 is in Luke's thinking, it is worth reading it again and comparing its imagery and language with Luke's.