"Ah, but I didn't say that the big bang must be 'NO natural mechanism.' I said, 'No KNOWN natural mechanism. There are sound empirical reasons for ruling out known natural mechanism.' An important distinction."
Then I'm confused. When I wrote my first post, I said that the history of science was against Buckna's suppositions because in the entire history of science no phenomenon had ever been discovered that could not be explained by natural explanations, even though there were several candidates that could have fit that bill. My point was that historically speaking the "no natural mechanism" conclusion was a failure. Your reply was, "There is one event. The Big Bang." That sounded, and still sounds like, you meant that the Big Bang was the one known phenomenon that might require a "no natural mechanism" conclusion. Now you are saying that was not what you meant, but if that is true then you have just lent support to my claim that Buckna's "no natural mechanism" conclusion is not tenable.
"Science can study some unrepeatable events. Science can try to determine, to the best of its ability, what the conditions were before the event, what the conditions were after the event, and what natural mechanisms might have been operating during the event."
OK, let me try to explain this again. The purpose of science is to explain natural phenomena. Any explanation science develops must be testable. Yet the only way that science can test an explanation is if the phenomenon being explained is repeatable, either in nature or on demand in a laboratory. In your above example you make very clear that the event in question is unrepeatable; therefore science could never develop an explanation for it because science could never test that explanation. At best science might be able to describe what happened; these descriptions are called schemes. But a scheme could never substitute as an explanation, because we could never know if the same pattern described in the scheme would have occurred again if the event had repeated itself. So science cannot explain unrepeatable events, even if certain scientists might investigate them to try to describe what happened. Such events, however, are trivial as far as overall science is concerned.
"By contrast, in the case of first life on earth --- another 'unrepeatable' event (unrepeatable given our present level of knowledge)...."
But abiogenesis is not an unrepeatable event. Explanations can be tested because we can recreate the events that might have occurred in the laboratory. What you mean is that the exact history of the emergence of life on earth is an unrepeatable event; that can only be described. But the mechanisms that were involved and the steps that were most likely taken can be repeated and so can be explained. We may never be able to prove the exact history of abiogenesis on earth, but we can prove how it most likely happened.
"Given enough of this kind of information, scientists could potentially conclude that some unrepeatable event happened via 'no known natural mechanism.'"
But they could never scientifically prove it, because they never explained how it happened; all they could ever do is describe what happened. As such, any conclusion would be meaningless.
However, I also see what the problem may be. When I offered my comments on this thread, I discussed only the third of Buckna's three options, the "no natural mechanism is possible" option. Your previous posts seemed to be defending this as a viable conclusion. So I tried to point out that in fact it wasn't. Since then, however, you have been ignoring it and instead been discussing the "no known natural mechanism" options. In essence, we have been discussing apples and oranges. So let me ask you point blank: Do you believe that the "no possible natural mechanism" option is viable?
"If someone can offer sound empirical models ruling out all known natural mechanisms, I would call that positive evidence for the 'no known natural mechanisms' hypothesis."
You are avoiding the question. Models are not themselves evidence; rather like hypotheses and theories they are based on evidence. You are also equivocating. I am not talking about the second of Buckna's conclusions -- "no known natural mechanisms" -- but the third -- "no natural mechanism is possible." So again I ask you, what kind of positive empirical evidence could there be that would convince you that the only viable explanation is the "no possible natural mechanism" conclusion?
"Now, suppose I do conclude 'no known natural mechanism' for some phenomenon or historical event. Moreover, suppose I conclude that the scientific data, theological data, and other relevant data strongly favors the 'supernatural miracle' hypothesis."
In any scientific investigation, the only relevant data is scientific data. If you are going to claim that some phenomenon is best explained by invoking supernatural forces, you are going to have to offer scientific data to support that; theological or other non-scientific data will be irrelevant. So what kind of positive scientific data could you find that would convince you that the best explanation would be a supernatural one?
"At that point, I would suspend searching for naturalistic explanations. I would devote my scientific energy elsewhere, to other problems on which I think I could more usefully spend my time."
Unless you were independently wealthy, the realities of the politics involved in modern scientific research would not allow you to do that. It is regrettable, but it is also true. Very few scientists could afford to simply drop a line of research and switch to a completely different line of research, especially if their only excuse was, "I can't explain how it works right now." By necessity they would continue to look for natural mechanisms, and you know what? Considering again the history of science, no one has ever found any evidence that convinced them that any particular phenomenon or event could only be explained by supernatural forces. With that kind of precedence it is highly unlikely that any scientist would in fact follow your example.
Kevin L. O'Brien