The Gospel Authors' Witness To Each Other

We often think of the evidence for the authorship of the gospels in terms of internal evidence and external sources of the patristic era, like Papias and Irenaeus. But we should also think in terms of the testimony of earlier sources, including the evidence the gospel authors provide for each other.

An example is what a source cited by Papias, probably John the son of Zebedee, said about Mark's gospel. For more about that material in Papias, see here.

If Mark's gospel was used as a source by one or more of the later gospels, as is widely believed, then that tells us something about how those later sources viewed Mark. The traditional view that the gospel of Mark was written by a disciple of Peter, with Peter as that disciple's primary source, makes a lot of sense of the use of Mark by later authors. By contrast, the popular modern view that the gospel of Mark circulated anonymously for a long time, often thought to have happened until well into the second century, makes less sense of how highly Mark's gospel was regarded early on. This sort of consideration doesn't tell us who wrote Mark, but it does give us some significant information and increases the plausibility of the traditional view and weakens alternative views, like the anonymous gospels hypothesis.

Something else to consider here is that Mark is occasionally named in close proximity to Luke, with the two of them sometimes being close by or together (Colossians 4:10-14, 2 Timothy 4:11, Philemon 24). That increases the plausibility of their knowledge of and use of each other's work, particularly Luke's use of a gospel by Mark.

If Luke used Mark's gospel as a source, whereas Mark didn't use the gospel of Luke, as is most commonly believed, then the relationship between the two men and their gospels is more evidential in support of Mark than in support of Luke. Still, it reflects well on Luke to some extent. Mark was willing to associate with Luke in the manner we see reflected in Paul's letters, and Luke's use of Mark's gospel makes more sense if Mark had a higher rather than lower view of Luke.

Similarly, the gospels of Mark and Luke and Acts present a positive view of Matthew and John. Matthew portrays John positively, and John does the same with Matthew. None of them suggest that any of the gospel authors died too early to have written the work attributed to him or anything like that. None of them are portrayed as an apostate like Judas or as having died early like James the son of Zebedee. The comments about Peter in John 21:18-19 have him living to be "old", which goes well with his living long enough to have a disciple who would compose a gospel based on Peter's testimony in the timeframe when the gospel of Mark is thought to have been written.

Some of these factors are of less significance, and some are of more significance. John's comments on the gospel of Mark, as recorded by Papias, and Luke's use of Mark as a source are highly important, whereas the other factors I've mentioned are less significant. These points are all worth considering as part of a cumulative case, though.