Precise applications of the Q theory vary widely, but generally speaking it's held to be earlier than (or at the latest contemporary with) Mark, and having its roots in the first recollections of Jesus' words by those that followed him during his ministry.
Whilst New Testament studies is a broad field, there are nonetheless two major camps, though there is considerable divergence within each. On one side we have what we'll call the conservatives. Broadly speaking they hold to the position that the gospels are, if not actually infallible, an historically accurate representation of what occurred in the life of Jesus. On the other hand we have the liberals who reject this position, believing that the best way to access Jesus and his teaching is by historical reconstruction using the gospels as key sources.
Now I should be clear that I am not claiming that those who believe in Q do so purely because it suits their ideological beliefs. Nevertheless, it is interesting that Q theory does suit both groups rather well. For this latter group the presumed antecedence of Q suggests that it is also more historically reliable. As a result the ethical teacher Jesus we would find were a copy of Q ever to be discovered is a supposedly more likely reconstruction than Mark's apocalyptic exorcist and miracle worker. In a context where exorcism and apocalypticism seem 'a bit weird' but the power of words is greatly appreciated, it's not hard to see the appeal of the Q theory.
Conversely were the Farrer-Goulder-Goodacre theory to be correct (i.e. that Matthew used Mark and then Luke used both Matthew and Mark) then this would suggest that the miracle working Jesus we find in Mark is the most historically probable, and that there's an increased chance that the ethical teacher is the invention of the early church.
For the conservatives the appeal is slightly more straightforward. Agreement with Q theory not only gives them a degree of academic credibility - they agree with the scholarly consensus on this crucial issue - but it also bolsters the reliability of the later gospels. The gap in time may remain the same but Q acts as a crucial stepping stone providing reassurance that the Jesus of the gospels really does correspond to Jesus as he actually was.
As I said above, the convenience of the Q theory isn't necessarily the reason why any given scholar believes in the theory. It does mean however that Farrar theorists (and other Q-sceptics) have their work cut out in overturning such a sizeable majority.
Edit: In the comments, Mark Goodacre mentioned something that I meant to say when I originally posted this. It stands to reason, of course, that those who reject Q may also be doing so for ideological reasons, myself, no doubt, included.
Labels: Historical Jesus