I am a humble country parson and no philosopher or biblical scholar. But since this comes up so often especially in regards to religious discussions, I thought I should take a stab at this.
What is naturalism? As I am hearing it, naturalism is a presupposition or assumption that the supernatural does not exist. Appeals to divine agency or miracles regarding natural or historical events are automatically ruled out. There could be (and probably are) scientists and historians who are naturalists in this sense--absolute naturalists, I guess you could call them.
In Perry Kea's article, The Road to the Jesus Seminar, he writes:
The quest for the historical Jesus was a product of the Enlightenment. The Enlightenment was an intellectual movement in eighteenth-century Europe and North America that promoted reason as the sole standard for establishing matters of truth. The ramifications were enormous. The political underpinnings of the American and French revolutions were established by Enlightenment figures (for example, Locke and Voltaire). The scientific method was born out of the Enlightenment. The privileging of reason over other modes of knowledge (such as tradition) meant that history was brought "down to earth" so to speak. The reasons why things happened in the past had to be sought within the space-time continuum of human life without appeals to divine agency. Just as the scientist could not appeal to supernatural forces to explain natural events, so the Enlightenment historian could not claim that historical events happened because "God so willed it."Does this make Perry Kea an absolute naturalist? I don't know. Perry could be one, but I don't think this statement is necessarily an argument for absolute naturalism.
When scholars informed by the Enlightenment considered the figure of Jesus in the gospels, they began to ask if the claims made for Jesus could be supported by rational evidence or arguments. So began the quest for the historical Jesus.
One of my commenters used the phrase practical naturalism. Practical or pragmatic naturalism does not automatically rule out the supernatural. In order for science and history to be consistent, we work with the assumption that natural events and historical events can be evaluated and explained by natural forces as opposed to supernatural ones.
What is the alternative? You could appeal to special revelation or tradition but this ends up being confusing. If we thought we could appeal to divine agency to explain things, where do we stop? How are we proven wrong? You can say most anything. People often do.
I think the charge of "naturalism" against the Jesus Seminar or other scholars of Christian origins is misplaced.
First, most of those who will use that label are in fact naturalists themselves when it comes to someone else's religion. John Loftus, author of Why I Became an Atheist says something to the effect that most Christians are atheists. They don't believe in the gods of other religions. Those whom they in turn call atheists are simply people who don't believe in one more god. These Christians are naturalists for everything in the universe except they suspend it for their own religion.
Second, historians and scientists don't need to resort to naturalism to deal with events. Most of the time we ask what is probable? What is the probable reason for the existence of this text that reports this event? Sure, it is possible that God answered Elisha's call by summoning bears to maul 42 boys for calling Elisha "baldy." It is possible that Jesus walked on water, turned water into wine, turned clay birds into real ones, and ascended to heaven. It is possible that Muhammad ascended into heaven to join him. All of these "events" are possible. Historians ask what is probable regarding how these stories came to be told.
I don't expect to convince anyone. I just wanted to put my thoughts down.
It does lead to the question of faith. What is faith? Is faith a belief in the supernatural? Is faith the suspension of naturalism when it comes to our preferred religious texts? Must you have this kind of faith in order to be a Christian?
Some say yes I suppose.
I am fine if folks believe that. Personally, I think faith is something different. But I am not exactly sure what that something is. It is for me related to these texts (of my religion mostly), but of other religions as well. Something in them summons something in me. Not only texts. The natural world in all its mystery summons me as well. It makes me more comfortable in my own skin and helps put one foot in front of the other. I call that faith. For now, I am OK with that.