Nearly a week ago Eddie mused about ' What Does it Mean to "Be Critical" in Studying the Historical Jesus'? If I understand his post rightly, his basic thrust is that historical Jesus research ought to attend to two different tasks: (a) assessing the general relationship between the primary sources (i.e., the gospels) and the actual flow of events that is 'history', and (b) on the strength of that relationship, analysing whatever individual traditions we are interested in. Also, if I read him right, scholars should set themselves to these two tasks in this order. I think this is a basic 'hermeneutical circle' problem, in that I would doubt that we can perform either task apart from some tentative conclusions about the other. My stance on the reliability of the gospels undergirds my treatment of any part of them, and my treatment of individual gospel units affirms or subverts my stance vis-à-vis the gospels as wholes. But it also seems to me that the concept of the reliability of a source (as a whole) is a slippery thing to quantify. Per my perspective on authenticity in general, I find 'burden-of-proof' comments that those for or against the general trustworthiness of the gospels have to argue their point difficult to agree with because they allow us to rest upon our presuppositions. I think Sanders had it right: the burden of proof falls on anyone who wants to prove anything, and this applies both to those who generally trust the gospels and those who generally doubt them.
But I think Eddie is right that, too often, the results of our analyses of individual gospel units is prevented from informing our views of the gospels as wholes. A similar point is made by Stan Porter, who writes
. . . genre theory is often neglected or misunderstood by Jesus scholars. The level of discussion of much historical Jesus research is in terms of individual pericopes. These form the basic units for comparison among Gospels and analysis in relation to extra-canonical sources. However, this level of analysis assumes the form-critical agenda, but fails to consider the Gospels in terms of the kinds of family resemblances that are relevant to biographies or, to use the terms of genre theory, in terms of intrinsic generic characteristics. This is not to deny that biographies have individual units, such as stories, sayings, and speeches, but that these are not the basic units of analysis. When the larger patterns are considered, the Gospels are seen to reflect biographical literature in most if not all essential features. ('Reading the Gospels and the Quest for the Historical Jesus', Reading the Gospels Today, 42)
My point doesn't concern genre criticism per se, but rather that the quality of the gospels' biographical testimony in its parts ought to affect our stance toward them as wholes.
To illustrate, I have argued elsewhere (no link available, sorry) that the Markan aside at 7.19b ('Thus he cleansed/declared clean all foods') is an important indicator of the evangelist's ability to distinguish Jesus in his own historical and theological context from his significance for the evangelist's circumstances. In a nutshell, Mark is able to state baldly that Jesus did make all foods acceptable for consumption, but he does so without putting a statement to that effect into Jesus' mouth. In other words, Mark doesn't write 'Jesus said, "All foods are clean"', but he does understand it to be the legitimate/inevitable outcome of what Jesus did say.
(Note: James Crossley argues for a different reading of Mark 7.19b altogether, largely on the basis of his early dating of Mark. While I remain sceptical of James' reading [viz., that Jesus said it was okay to eat all kosher foods irrespective of the condition of one's hands] it is still possible that later readers of Mark [interestingly, apparently not Matthew] may have read Mark 7.19b as making it okay to eat pork, or perhaps even meat sacrificed to idols [cf. 1 Cor. 8-10]. If James is right, then all this is, of course, speculative. But he isn't right, so this isn't speculative.)
The point, then, is that if Mark is able at this instance to make Jesus' story relevant to his circumstances without rewriting Jesus, then this ought to affect the way we approach Mark's gospel as a whole. If Mark demonstrably avoids retrojecting what he wants Jesus to have said into his mouth, at least in this instance, then we should avoid the cavalier assumption that Mark retrojected his own circumstances onto Jesus' life without better argumentation. This is particularly the case with respect to Sanders' (and many others') view that the conflict stories, especially, reflect the early Christian communities' conflict with post-70 Judaism as the latter went about reconstituting itself after the destruction of Jerusalem. The significance of Jesus' conflict with his contemporaries was certainly apprehended from the point of view of later (emerging) Christianity, but I suspect the evangelists are hardly responsible for making up the theme as a whole. We should still be on the lookout for how the tradition appears to have developed in the Markan narrative, but we should also be just that much more confident that Mark was, in fact, interested in Jesus for his own sake.