IT'S MORE OF A PUZZLE, REALLY
The word "synoptic" comes from the Greek and literally means "seen together." The Books of Matthew, Mark, and Luke are called the "Synoptic Gospels" because they contain much of the same material and largely follow the same outline. They can be laid out in parallel columns for comparison and study. These three Gospels can be seen together.
The Gospel of John goes its own way. It is made up mostly of unique material and doesn't lend itself easily to comparison with the other Gospels.
The Gospel of Matthew contains roughly 90% of the Gospel of Mark. Luke contains a little more than 50% of the Gospel of Mark. Matthew and Luke also have some material, mostly teachings of Jesus, in common that is not found in Mark. All of the synoptics have some material found in none of the others.
The "Synoptic Problem," as scholars call it, is the question of just how these three Gospels are related.
The most commonly held solution to the Synoptic Problem is the so-called "Two Document Hypothesis." This theory postulates that Mark was written first. Matthew and Luke both had copies of Mark which they used as one source for their own writings. Matthew and Luke also had another common source, a hypothetical, probably written, collection of sayings that scholars call "Q."
The designation "Q" probably comes from quelle, a German word meaning "source." The simplest definition of "Q" is material found in both the Gospels of Matthew and Luke but not in Mark.
So, the Two Document Hypothesis holds that Matthew and Luke, working independently, both used Mark and the hypothetical Q as sources for their own Gospels. They also included a certain amount of their own material, referred to as "M" for Matthew, and "L" for Luke. The Two Source Hypothesis is often illustrated with a diagram like this one:
Although the existence of Q is strictly hypothetical, the International Q Project, a group of notable New Testament scholars, worked to reconstruct its text as nearly as possible. Using their knowledge of how Matthew and Luke used Mark, they built what they believe to be the nearest possible approximation of what an actual Q source would have looked like. Based on this work, some scholars claim to have found two (or is it three?) layers of tradition in the Q material and have even proposed a structure for what the community that produced Q would have looked like. It is fascinating work (at least to a New Testament geek like me) but seems an elaborate structure to build on the shaky foundation of a hypothetical document.
There are other possible solutions to the Synoptic Problem. The strongest contender is the "Farrer Hypothesis" (also known as the "Farrer-Goulder-Goodacre Hypothesis" after some of the prominent scholars who have championed it). The Farrer Hypothesis does away with the need for hypothetical sources. In this scenario Mark was written first, Matthew expanded upon Mark, and Luke was written using both Mark and Matthew as sources.
Other possible solutions to the Synoptic Problem have been proposed, but the Two Document Hypothesis and the Farrer Hypothesis have the best scholarly support. There are also highly nuanced variations of these two hypotheses.
As a student of the Bible, I find all of this quite fascinating. As a preacher, I am less concerned with the solution to the Synoptic Problem than its very existence. Paying attention to the way that Matthew, Mark, and Luke handle the same material helps me better understand what each author is trying to say. Understanding a text is a necessary step before proclaiming it.
Coming soon: The Real Solution to the Synoptic Problem. I found the illustration of the Two Document Hypothesis at this website.