SPROUL: There are different methods. The main method is through external sources, by looking at what the ancient extra-biblical writers would quote. For example, if a text of Scripture was quoted by Eusebius, and you know when Eusebius lived, then that helps to date the book. You also do this by looking at internal references and first-century history to see where the weight of the evidence falls.
Of course, this becomes a matter of huge controversy with higher criticism. The higher critics have, for the most part, forced the majority of the New Testament writers into the second century, although there has been some softening of that critical aspect in more recent years.
THOMAS: Yes, external sources for sure help with this. In many cases, we would have some very specific information about when certain books were written. There has been a great deal of discussion about the New Testament books. In the earlier part of the twentieth century, there were those dating them fairly late, but now, even liberal scholarship has moved those dates way back into earlier parts of the first century and therefore within the period of the Apostles who purportedly wrote the New Testament books.
SPROUL: Sometimes philosophical and critical theories are in play. For example, Old Testament books include predictive prophecies that naturalists believe are impossible. They will argue for the theory that these books are vaticinium ex eventu, that is, these statements had to be written after the history had been fulfilled, because they just don’t believe in predictive prophecy. So, those theological and philosophical considerations play into the dispute as well.