Marcan priority

So if we know they were copying, from whom were they copying? Alongside the documentary solution to the Synoptic Problem, the most broadly accepted tenet in the study of the Synoptic Gospels is that Mark was first.

Or to use the scholarly jargon, Markan priority.

Markan priority is the supposition that Mark was written first, and according to virtually all scholars working on the synoptic problem today, the authors of Matthew and Luke copied extensively from Mark's gospel.

Why do scholars think this? First, the idea that Matthew and Luke used Mark is more plausible than the alternative, that Mark used Matthew and Luke.

That is, based on everything we know about first-century Christians and these gospels, it's easy to understand why someone would write Matthew or Luke if they had a copy of Mark in front of them.

Why would Mark conclude his gospel without including those stories? And it's important to note that this is not reversible.

It makes all the sense in the world why Luke reading a copy of Mark would make the additions that he did.

You would read through Mark and be like, "Whoa, where is the birth story? Where are the post-resurrection appearances to his disciples? I better add to this in my own version." This is only the first line of evidence that supports Markan priority.