Right about now, we are probably going to get some objections from both sides on our presentation.
Objections from Synoptic scholars
On the one hand, scholars are going to object that we haven't examined the details of Luke's treatment of Mark (or vise versa), which provide critical (and perhaps conflicting) evidence, and paint a much more complex picture of how these books were composed. Furthermore, they will object that we haven't taken into account the other gospels, which, depending upon where they are placed chronologically, in a 'dependance' tree, might have more to say on who copied what and when.
Objections from Fundamentalist Believers
On the other hand, our Christian brothers and sisters are going to demand some sort of explanation of how Divine Inspiration, Preservation, and Biblical Inerrancy are supposed to fit into this picture.
Since those who are first will be last, and those last first, we will deal with scholarly objections first (hoping they will end up last! - a small joke).
Scholarly Objections Discussed
Have we really adequately and fully explained the relationship between Mark and Luke?
Of course not.
To do so would require a minute analysis of both gospels (and indeed all the others etc.) section by section, and verse by verse.
But we have not here 'glossed over' the details. We have simply taken on the more modest goal of presenting the basic outline of correspondence and positioning of the main sections of each gospel.
A complete analysis would take 20 volumes of discussion, and a lifetime to compose.
But there is a much more reasonable objection which can be addressed in the here and now:
Who Copied Who
How do we know that Luke copied Mark, and not vice versa (the other way round)?
This is a fair question, and one that we can apply some evidence and arguments to.
Along with the two possible scenarios, we also have two possible motivations and purposes to explain:
(1) If Luke copied Mark: In this case, we can easily account for Luke's purpose, because he has important new material, namely a collection of Jesus' teachings to incorporate into Mark and share. As well, it is an opportunity to make the gospel more universal and useful to non-Jewish Christians and potential converts.
(2) If Mark copied Luke: What possible motive could Mark have for deleting twelve whole chapters of Luke? Well, we could suppose he wanted to produce a "Reader's Digest" version of the gospel, a kind of "Luke for Dummies".
But against this idea of Mark stripping down Luke into a kind of newspaper synopsis are the following facts:
(a) Mark's version of each incident is usually bloated with unimportant incidental details that add little to the story. If Mark's goal was to shorten Luke, it would counter-productive to expand every remaining section to make it longer, without any new insight or even improvement in sense. On the other hand, Luke appears to have cleaned up Mark's diction immensely, deleting the irrelevant and making for an efficient telling of the story. Where Luke does add glosses (i.e., Luke adds 19:14, 22, 27 to the Parable of the Minas/Talents: Luke 19:11-27 = Matt. 25:14-30) they are plainly explanatory. Mark just appears wordy.
(b) Most of the deletions, substitutions and insertions in Luke have simple explanations if Luke copied Mark. But it would be difficult to explain why Mark would remove the milder dispute at the Last Supper (Luke 22:24-30) and replace it with the harsh bickering over princely thrones (Mark 10:35-45), or why Mark would delete the 2nd Lamentation of Jesus (Luke 19:41-44) and replace it with the cryptic Fig Tree lesson (Mark 11:12-14, 20-26).
(c) Luke tells us he is fully aware of those who have written previous accounts, and about his goal of making a more complete account. Since the evidence from Mark also fully supports Luke's claims, it is the obvious, most reasonable interpretation of the facts. Luke used something that looks almost identical to Mark as a base, and we might as well admit it was in fact Mark that Luke used.
These considerations are equally convincing for believers and unbelievers, scholars and fundamentalists. That is why a majority of scholars believe Mark came first, not Luke.
It makes no sense to insist that Mark copied and mutilated Luke, and besides flying in the face of the plain evidence, it cannot be a satisfactory position to take for fundamentalists either, since it would paint Mark as either an idiot or a vicious satirist intent on spoofing or attacking the gospel of Luke.
Common sense, scholarship, and faith work together to support our view that Mark came first, and Luke used him reverently as a basis for his own gospel.
EDIT:
Mr. Scrivener has turned the first page of posts here into an html file, and created a special section on our website which will relate the Synoptic Problem to the question of the Authenticity of John 8:1-11. You can download a more convenient form of the material there:
Part I: Mark and Luke <-- Click Here.