The first three gospels in our NT are called the ‘synoptic’ gospels. They share a lot of material, and it seems very clear they were written with a great deal of mutual influence. Unpicking the particular pattern of influence is a tricky puzzle, commonly called the “Synoptic Problem”. Currently the most widespread view is that Mark was first (known as “Markan priority”), then both Luke and Matthew used Mark as a source, along with another shared source (known as “Q”, short for the German “quelle” which just means “source”) that Mark did not have access to. I’m not so sure, I tend towards a more complex picture that is somewhere between this and the “Farrer” hypothesis, which says that Mark was first, then Matthew used Mark, then Luke used Matthew*.
These debates are played out based on the patterns of sharing between the gospels. Obviously the same stories are found in multiple gospels (although, surprisingly very few are shared between the Synoptics and John – other than a couple of key events, John seems to have a conspicuously different life of Jesus). But beyond the same stories, the exact same words are often used, in idiomatic ways that are very unlikely to be coincidence. At other times there are signs that one writer has copied another, wanting to make intentional changes, and then got bored as they wrote (known as ‘Fatigue’). For example in the well known parable of the talents, Luke (19:17) has the servants given “cities” initially, but is obviously copying the same text Matthew uses (Matt 25:21 doesn’t say specifically what they are given), because by the end of the parable Luke has reverted to calling them talents as Matthew does.
When you learn about the synoptic problem, your homework is to colour in synoptic parallels: versions of the gospels printed with the same story from each gospel printed side by side. In this way you can see the material and the phraseology that is unique to each gospel, that is shared between each pair, and that is common across all three.
Now in the modern age, we can program computers to do our homework for us. And behold: a complete colour map of the synoptic gospels.
In this map the three columns represent the three gospels, Matt first, then Mark, then Luke. Each small square (2×2 pixels) in the diagram is one Greek word (from the Nestle-Aland 27 diplomatic edition), so the size of the column tells you the relative size of the gospel (Mark is by far the smallest). The words are from left to right and top to bottom, just as you’d expect.
The color of the pixels tells you whether the word is shared in that story between the gospels (so there’s some complicated matching behind the scenes to compare equivalent stories, no matter which order they appear, and then map them back out into the proper order for diagramming). The color key is:
Red – Matthew’s gospel only.
Green – Mark’s gospel only.
Blue – Luke’s gospel only.
The other colors are combinations of Red, Green and Blue light:
Red+Green = Yellow – Matthew and Mark only.
Red+Blue = Magenta – Matthew and Luke only (so called “Double tradition” material, normally associated with the Q source).
Green+Blue – Cyan – Mark and Luke only.
And finally all three gospels agreeing is shown in black (I know, it should be white, but white is difficult to distinguish from the Yellow and Cyan).
So the diagram tells you an awful lot about the gospels: it shows that virtually none of Mark is unique to Mark. It shows the big block of magenta material near the start of Matthew and Luke which is the sermon on the mount and other so called “sayings” material of Jesus – the stuff that is thought to come from Q. It shows there is a lot more Yellow than Cyan, so Matthew sticks to Mark far closer than Luke does. And it shows there is more Magenta than Cyan, so Luke sticks far closer to Matthew than to Mark (giving further credence to the idea that Luke used Matthew who used Mark). You can also see that the birth narratives at the start of Matthew and Luke are very different, and that Matthew and Luke also have a number of other large blocks of original material.
So the colouring scheme used here is based on words in stories. there are other ways of dividing this up. In particular you can divide it just by which stories are shared. This doesn’t tell you as much historically, since we can’t tell if the stories were copied from one another or just in common circulation. But if you colour that way you get very different amounts of each color. You get much more black, for example – which is to say that the gospel writers often all write the same story, but in quite different words.
The final thing to say is about John. I said John is very different. How different? Well I couldn’t put John in the same diagram as above, because I didn’t have enough distinct colours to clearly show the 15 different patterns of sharing between 4 gospels. But here is John on its own. In this diagram the brown color is the stuff that is only in John. The other colors are as before: the stuff that John shares with Matthew (red), Mark (green), Luke (blue), Matthew and Mark (yellow), Matthew and Luke (magenta), Mark and Luke (cyan), and all three of them (black). Clearly John is a totally different beast.
Anyway, I’ve written enough on this. I love diagrams like this – diagrams that are incredibly complicated and specific, but that the overall patterns can be seen from those details.
* If you know anything about this topic, then it might not surprise you to know that I was a student of Mark Goodacre, who is one of the most evangelical proponents of the Farrer hypothesis. I’m not sure I totally agree with Farrer, however, I tend to favour a more complex pattern of sources.