I saw this phenomenon illustrated recently in a discussion over at Dagoods' blog about dating the composition of the Acts of the Apostles. The book ends with Paul awaiting trial in Rome. Anette Acker, who blogs at Grace and Miracles, argued that Acts was written around 62 A.D. because it doesn't mention important events that occurred after that date. Dagoods and I argued that the author had other reasons for ending the story there. We argued that the book must have been written after the destruction of temple in Jerusalem in 70 A.D. because the author has Jesus foretell that event in the Gospel of Luke.
Anette insisted that our conclusion was being driven by our presuppositions about the impossibility of the supernatural:
The real question is this: How likely do you think it is that scholars would date Acts after the fall of Jerusalem if Jesus had not predicted it in Luke? Do you think that if it was written several decades later, it’s likely that Acts would have ended a) while Paul was in house arrest in Rome pending appeal, b) without mentioning the death of Paul, c) without mentioning the persecution of Nero, and d) without mentioning the Great Revolt and the fall of Jerusalem?Here’s the problem I see for the apologists who make this argument (and Anette is certainly not alone in doing so): The argument that Acts was written in 62 A.D--i.e., before Paul’s death, the Neronic persecution, and the fall of Jerusalem--depends upon the assumption that it is a human book. Only when a finite human writes a book can we infer from its silence about a particular event that the author doesn't know about the event and was, therefore, writing before the event occurred. God, on the other hand, knows everything that ever happens throughout all eternity. If a supernatural book omits mention of a particular event, we cannot conclude that its author doesn’t know about it or that it hasn’t occurred yet. That argument depends on the natural assumption that human beings cannot see into the future.
This is the problem: Biblical criticism is the study of the Bible as a human creation. By itself that is no problem, because the Bible can certainly be studied that way, like any other series of historical documents.
However, this means that everything is presumed to have a natural explanation. In other words, because Jesus “predicted” the fall of Jerusalem, critical Bible scholars have to date the Gospels—and by extension Acts—after 70 AD.
The real problem with this is that if you look to critical Bible scholars to help you decide whether the Bible is the word of God, they will give you only one possible answer: No. Why is that? Because the answer is already assumed in biblical criticism, which is “the treatment of Biblical texts as natural rather than supernatural artifacts” (Wikipedia).
Do you see the circularity in this approach if your question is whether the Bible is the word of God or just a human construct? In biblical criticism the presupposition is that the Bible is an entirely natural text.
So if you're approaching this in a neutral way, then the question is: Apart from the "prediction" of Jesus, what is the most likely explanation for why Acts ends the way it does?
However, if we assume that the Acts is a human book, then how can we avoid making the same assumption about the Gospel of Luke? If the assumption that human beings don't see into the future is valid when dating Acts, we have to conclude that that the detailed descriptions of the fall of Jerusalem in Luke are strong evidence that it was written after 70 A.D. It is conceivable that the author of Luke simply recorded the canny predictions of an astute military and political analyst, but I don't think that the historian can assess that as more likely than the much more common phenomenon of someone claiming to have foreseen important events only after the fact.
The real problem is that apologists want to apply the methodology of critical scholarship--i.e., methodological naturalism--only so long as it supports the conclusion that they wish to reach. As soon as it poses a barrier, they deride it as closed-minded and biased.