To the rule of Mark being middle term there are important exceptions: there are a handful of instances where Mark is clearly not the middle term. These passages where Mark is not the middle term constitute the most difficult phenomenon in the Synoptic Problem, because it so blatantly blurs the basic distinction between Triple and Double Traditions, thus more than anything else preventing the easy classification of everything into clear-cut, convenient categories that would otherwise be possible.
A good representative of this phenomenon can be found the Parable of the Mustard Seed (Matthew 13:31-32; Mark 4:30-32; Luke 13:18-19). where Matthew and Luke agree
against Mark in places.
Matthew: “The kingdom of heaven is like a grain of mustard seed that a man took and sowed in his field. It is the smallest of all seeds, but when it has grown it is larger than all the garden plants and becomes a tree, so that the birds of the air come and make nests in its branches.”
Mark: “With what can we compare the kingdom of God, or what parable shall we use for it? It is like a grain of mustard seed, which, when sown on the ground, is the smallest of all the seeds on earth, yet when it is sown it grows up and becomes larger than all the garden plants and puts out large branches, so that the birds of the air can make nests in its shade.”
Luke: “What is the kingdom of God like? And to what shall I compare it? It is like a grain of mustard seed that a man took and sowed in his garden, and it grew and became a tree, and the birds of the air made nests in its branches.”
One would notice some clear agreement between all three Synoptics (“
like a grain of mustard seed;” “
the birds of the air”), some agreement between Matthew and Mark (“
smallest of all the seeds…larger than all the garden plants”) and between Mark and Luke (“
What is the kingdom of God like?”). What is striking however is that there is also agreement between Matthew and Luke against Mark (“
which a man took and sowed…becomes a tree…in its branches”).
Also interesting is the placement of this parable. As we’ve mentioned countless times, Mark is usually the common element which means that one tends to not to find agreements in order between Matthew and Luke. Matters are different here, however, since both Matthew and Luke pair this with the Parable of the Leaven (Matthew 13;33; Luke 13:20-21), which does not appear at all in Mark.
Passages like this in which Mark is not the middle term appear in all three Synoptics and feature substantial agreement, either (or sometimes, both) in order and wording, between Matthew and Luke. Such are not very common and isolating them is not always straightforward, not least because the matter of agreement between Matthew and Luke is simply a question of degree. Every Triple Tradition passage features some agreement between Matthew and Luke against Mark; what one has to decide is whether to consider the agreement major, as in the passages we are now discussing, or minor, as in the majority of Triple Tradition material. Other passages which people have taken the agreement to be major include John the Baptist (Matthew 3:11-12; Luke 3:15-17; cf. Mark 1:7-8), the Testing in the desert (Matthew 4:1-11; Luke 4:1-13; cf. Mark 1:12-13), the Beelzebub controversy (Matthew 12:22-37; Luke 11:14-23; cf. Mark 3:22-30) and the mission of the disciples (Matthew 10:1-15; Luke 9:1-6, 10:1-12; cf. Mark 6:6b-13).
To sum, a review of the various data which comprise the Synoptic Problem.
1.) Triple Tradition: Found in all three Synoptics. The order of this material is similar across the three Gospels.
2.) Double Tradition: Found in Matthew and Luke but not in Mark. The order tends to vary between the two Gospels.
3.) Special Matthew (M): Found in Matthew alone.
4.) Special Luke (L): Found in Luke alone.
5.) M in Triple Tradition: Material unique to Matthew embedded in Triple Tradition material and would make no sense outside of context.
6.) Lukan Triple Tradition: Three pericopes which have parallels in Matthew and Mark and might be described as Lukan versions of Triple Tradition material.
7.) Not Quite Triple Tradition: Material found in Matthew and Mark but not in Luke or in Mark and Luke but not in Matthew. These are not, strictly speaking, Triple Tradition pericopes since they occur in only two Gospels, but they are akin to Triple Tradition because they appear in the Markan order.
8.) Mark being not the middle term: Some material halfway between Triple and Double Tradition. Appears in all three Synoptics but unlike Triple Tradition, features substantial agreement between Matthew and Luke against Mark.