...so is there such a thing as "historical fact?" And where do you draw the line between "historically probable" and "historically factual"?
That's a good question. Strictly speaking, no, there is no such thing as a historical fact. But of course that doesn't work well when we go to talk about history, simply because we'd have to throw in "allegedly" every second word
As for when it crosses the line from "probable" to "factual", it would likely have to be around the point when there's no serious academic opposition to the event/whatever in question. Even that's subjective, but it's the best you can do.
Anyways, I mentioned in the other thread about how I was writing an essay about sources from the early Roman Republic. There's a figure in the history of the Roman Republic named Gnaeus Marcius. He is referred to in almost every available source (Pictor, Livy, Plutarch, Appian) as a Roman noble who won renown in a war against the Volscians during the siege of the town of Corioli, and was bestowed the title "Coriolanus." Then almost every source goes on to recount his exile from Rome and his assumption of the leadership of the Volsci in another war against Rome. The sources claim he won a series of victories, and led his forces to the gates of Rome until he was turned away by the pleas of his wife and mother who still lived in the city.
Now, despite nearly every source recounting the latter part of that story (after the victory at Corioli), many historians now believe it didn't happen, and doubt the existence of the man himself. It's a case, BrotherH, where you can't take a historian's word at face value. Ultimately, a historical account (especially before the spread of historiographical writing, although Luke as a historian is in this category) is merely a basis for further research. One doesn't gauge historicity by drawing a "For" and "Against" column for a given historical (or non-historical) event. It's a lot more complicated than that.