The assumption here seems to be that because we do not know who authored the four gospels they therefore cannot be historical documents. It is true that scholarly consensus holds that the gospel authors are anonymous, although some scholars have forwarded reasons why they think we can know the authors by name. However, we shall go with the consensus on this one.
It misses the point to argue that because we do not know the name of the authors of the gospels that they therefore must be unreliable. Firstly, authorship isn’t the only the criterion for reliability, there is other criterion too that historians take into account. For instance, as long as historians can discern the traditions behind the gospels to be reliable then it is immaterial who authored it. If the gospels are early, corroborated by archaeological evidence, have ample manuscript attestation, and match in the core details then there is no reason why one should reject them. Exegete and philosopher William Lane Craig captures this, writing that “when you think about it, the names of the Gospels’ authors are quite immaterial. At most what matters is that the author, whether named Luke or Joshua or Herkimer or what have you, was in a position to deliver historically reliable information about the historical Jesus” (1).
A second point that skeptics often miss is that anonymity does not equate to “not knowing” about something. The fact that we don’t know who penned the Gospel of John doesn’t mean we don’t know things about the author. We may never know his name but we can know a number of things about him. Based on internal evidence we can know that he was a Jew, that he wrote for a Jewish audience, and that he knew about Jewish customs, Jerusalem & Jesus’ ministry. Although he was a Jew he is also evidently hostile to the Jewish enemies of Jesus. We can also know approximately when he, and our other gospel authors penned their works. In reference to Matthew’s author it is likely that he was a Christian Jew, that he was familiar with Jewish history, customs, ideas, and the classes of people as well as with Palestinian geography. Luke’s author was clearly educated, probably lived in the city, wasn’t a Jew or a Palestinian, and was a person who respected manual work. Mark wrote for a Greek & a gentile audience as seen in the author’s need to explain Jewish traditions and translate Aramaic terms. This audience was likely made up of Greek-speaking Christians probably in Rome although Galilee, Antioch, and southern Syria have also been suggested as alternatives (13).
Historians have a criterion they judged reliability with and such a criterion isn’t hampered if they don’t know the name of an author. It would have been nice to know the name, but it doesn’t entirely matter if we don’t. We also saw that anonymity doesn’t mean we don’t know things about an author. We can judge from the author’s own testimony who he was, where he probably lived, who his audience was, and when he was writing.
Craig, W. 2014. Gospel Authorship – Who Cares? Available.