Which source hypothesis has a simpler explanation of this data?

Any source theory needs to be supported by redaction criticism. It must be able to account for both narrative transpositions as well as any parallels or variations in content. To be considered plausible, a hypothesis should be consistent with each gospel's editorial tendencies at other points.

In the case of this particular pericope, an adequate explanation of why Luke decided to introduce the parable of the mustard (& the leaven) in a narrative context that differs from that provided by both Matthew & Mark is in order.

A hypothesis that presupposes that Matthew is the primary literary source of the synoptic material (Augustine or Griesbach) must also be able to account for the fact that both Mark & Luke:

• omit different details of this segment stressed by Matthew & yet
• introduce the parable of the mustard with rhetorical questions not used by Matthew.

A hypothesis that presupposes that Mark is the primary synoptic literary source needs to explain why both Matthew & Luke agree in material not recorded by Mark.  Most significant are:

• virtually identical versions of the parable of the leaven; &
• description of the mustard plant as a tree.

A	Did Mark edit Matthew?

Casual comparison of this section of the synoptic gospels seems to favor a source theory that presupposes the priority of Matthew.  For Matthew's version has most of the details associated with the parables of the mustard seed & the leaven presented by either Mark & Luke, particularly.:

• description of the mustard plant as both a large shrub (as in Mark) and a tree (as in Luke);
• the parable of the leaven (as in Luke);
• a narrator's summary about Jesus' teaching in parables (as in Mark).

Thus, the material in this pericope might be cited as evidence supporting Augustine's claim that Matthew's gospel was the ultimate literary source of this material. The shorter parallels in Mark & Luke could then be interpreted as selective revisions of the Matthean account. 

Augustine's characterization of Mark as an epitome of Matthew, however, is not an accurate description of the actual details of these passages.  True, there are 25 fewer Greek words in Mark 4:30-34 than in Matt 13:31-35.  Yet, this relative verbal economy is achieved not by Mark's condensation of the Matthean narrative but, rather, by Mark's omission of whole elements from Matthew's composition. 

Greek Word Count	Matt	Mark
mustard	50	57
leaven	23	--
summary	16	25
Ps 78:2	18	--
Total	107	82

As this table shows, the Markan versions of both the parable of the mustard & the narrator's summary are actually longer than the parallel passages in Matthew.  Therefore, if Mark edited Matthew he chose to elaborate on these two elements of this section of Matthew while dropping two others.

One can, of course, suggest plausible reasons for omission of the parable of the leaven & the citation of Ps 78 in Mark 4:30-34:

• the metaphor of leaven does not fit well with the seed motif of the three prior parables; &
• Mark does not often quote from Jewish scripture.

Therefore, if Mark knew the text of Matthew, his omission of these elements could be viewed as a deliberate editorial decision to make this section more consistent with both the dominant motif in this section on parables & with Mark's own general style. 

Likewise, Mark's omission of Matthew's description of the mustard plant as a "tree" can easily be viewed as an editor's elimination of surrealistic details from the Matthean version to keep the imagery of that parable in conformity with nature.

If Mark exercised such sound critical judgment, however, in polishing this section of Matthew, then the rhetorical & grammatical lapses in his presentation of the parable of the mustard seed are all the more difficult to explain.  For if Mark rewrote Matthew's parable of the mustard he would have

• doubled the length of the introduction to the analogy of the mustard seed by replacing Matthew's succinct declaration "The kingdom of heaven is like..." with two rhetorical questions ("How shall we compare...? What parable shall we use...?") that are redundant & out of place at this point in his narrative; and
• replaced Matthew's grammatically correct Greek (two complete well-formed sentences) with a very clumsy construction (an incomplete sentence -- with no explicit subject or main verb -- beginning with a free-floating prepositional phrase ["As a grain of mustard"] followed by a hodge-podge of relative & independent clauses); and
• introduced redundant wording that was not derived from the text of Matthew: i.e., "when it is sown...yet when it is sown" [Mark 4:31-32] & "upon the earth...upon the earth" [Mark 4:31].

Such rhetorical & grammatical clumsiness is hard to reconcile with the claim that Mark edited Matthew.  For Matthew's constructions are more literary than are Mark's. If Mark had direct access to a copy of the gospel of Matthew, it is a complete mystery why he took so much liberty in replacing Matthew's polished wording with flourishes that are both stylistically inferior & logically superfluous.

Thus, the Augustinian hypothesis of Markan dependence on the text of Matthew results in portraying Mark as a literary butcher, who, instead of summarizing his supposed source, inflated it with superfluous wording that ruined the clarity of the Matthean text.

B	Did Mark conflate Matthew & Luke?

Griesbach's synoptic theory can resolve one of the problems with the traditional Augustinian source hypothesis by crediting the non-Matthean rhetorical questions that introduce Mark's parable of the mustard seed to the influence of Luke.  In Luke 13, those questions about an appropriate parable for the kingdom of God are perfectly in order.  For, unlike Matthew & Mark, Luke does not append the parable of the mustard to other seed parables or kingdom sayings.  Rather, Luke deliberately distanced the analogy of the mustard seed from his presentation of Jesus' discussion of the parable of the sower (Luke 8) by introducing it five chapters later. [For the precise relative position of these pericopes in each gospel, see my synoptic outlines.] In fact, since Luke reports none of Matthew's parables of the kingdom except the parables of the mustard & leaven, it makes eminent sense for him to introduce this pair of parables with Jesus' twofold question about a fit analogy for the kingdom.  So, Mark's decision to preface the parable of the mustard with rhetorical questions might be interpreted as evidence of his knowledge of Luke.

Why Mark would borrow this particular Lukan rhetorical flourish, however, is a redactional mystery. For, like Matthew but not Luke, he

• links this parable to his discussion of the parable of the sower &
• appends it directly to a parable that explicitly uses seed imagery as a metaphor for the kingdom of God.

Thus, Jesus' invocation of these rhetorical questions at this point in Mark represents a mental lapse on the part of both author & subject.  For it is a logically awkward & unnecessary interpolation in the Markan narrative that creates the impression that Jesus was a speaker who could not remember what he had just said.

A further problem with Griesbach's hypothesis is that none of the other details in this segment support the idea that Mark conflated the other synoptics, since Mark regularly omits elements that are the same in both Matthew & Luke's versions of this pair of parables. Not only does Mark not report the parable of the leaven at all -- despite the fact that practically all the wording in the other two synoptics are virtually identical --, his version of the parable of the mustard seed also lacks phrases in which Matthew & Luke's texts are in virtual verbatim agreement:

• "...which a man took...." [Matt 13:31//Luke 13:19]
• "...and becomes/became a tree..." [Matt 13:32a//Luke 13:20]
• "...in its branches" [Matt 13:32b//Luke 13:20].

While there are 18 Greek words that are identical in Matthew's & Luke's versions of the mustard seed parable, only 6 of these -- κόκκῳ σινάπεως ("grain of mustard seed") & τὰ πετεινὰ τοῦ οὐρανοῦ ("birds of the air") -- are found in Mark.  In fact, aside from the pair of rhetorical questions introducing this parable, Mark does not share any wording with Luke that is not also found in Matthew. Moreover, Mark's formulation of these rhetorical questions differs from that found in Luke.  

So there is no clear verbal evidence in this pericope to support the idea that Mark was in any way dependent upon the written text of Luke. Not only does Mark introduce the parable of the mustard seed at a point in his narrative syntax that is parallel to Matthew rather than Luke, the Markan wording of this parable is much closer to the Matthean version. In cases where Luke diverges from Matthew, either by omitting words or presenting variants, Mark's wording regularly parallels Matthew's. For example, both Mark & Matthew

• describe the mustard seed as "sown" (Luke has "tossed") 
• characterize it as "the smallest of all seeds" (not in Luke)
• characterize the full grown plant as "the greatest of shrubs" (not in Luke)
• conclude "so that (not in Luke) the birds of the air...make nests" (Luke uses a past tense).

Moreover, since Mark omits phrasing common to Matthew & Luke, Griesbach's hypothesis forces one to conclude that Mark was so opposed to the Lukan version of this parable that he used it as a negative filter, deliberately deleting from Matthew most of the details that Luke reports (except for mustard seed & birds) & leaving only elements of Matthew's description that had no parallel in Luke.  

Finally, rather than reproduce Matthew's succinct syntax, Mark introduces redundant wording & altered imagery not found in either of his alleged sources:

• "when it is sown...when it is sown" [Mark 4:31-32]
• "on the earth...on the earth" [Mark 4:31]
• "it rises up and becomes" [Mark 4:32]
• "and puts forth large branches" [Mark 4:32]
• "in its shade" [Mark 4:32]

These variants combine with Mark's redundant non-Matthean rhetorical questions to inflate his version of this parable, making it longer & rhetorically more cumbersome than those presented by either Matthew or Luke. Thus, this pericope does not confirm Griesbach's contention that Mark "tried to be brief", or that he "followed Luke."  If Mark was trying to be brief, he should have followed Luke's shortest version of the mustard seed parable itself, introduced it like Matthew without redundant rhetorical questions & refrained from adding superfluous wording of his own invention.  The fact that he did none of this indicates the difficulty of accounting for the evidence in this pericope on the basis of the Griesbach hypothesis.

C	Did Luke use Matthew?

Since Mark presents the most grammatically awkward version of the parable of the mustard seed & lacks the parable of the leaven, any synoptic source hypothesis that presupposes Markan priority is easier to defend than those that posit Matthean priority. For polishing & insertion of thematically relevant material are normal editorial practices. 

In Matthew the mustard seed parable & the generalizing summary regarding Jesus' use of parables are worded more economically than the parallel elements in Mark [see chart above].  Yet Matthew includes logical elements not derived from Mark:

• "which a man took" [Matt 13:31]
• "and becomes a tree" [Matt 13:32]
• "to the crowds" [Matt 13:34].

The fact that the first two of these elements & the non-Markan parable of the leaven are found virtually verbatim in Luke may seem to favor Farrer's thesis that Luke knew & used the gospel of Matthew. Yet that hypothesis is the simplest solution only in accounting for added non-Markan wording common to Matthew & Luke. If one supposes, that Luke used the text of Matthew as well as that of Mark, then one must also be prepared to explain 

• why he omitted elements in the parable of the mustard seed shared by both Matthew & Mark [see above] & 
• why he placed this pair of parables in a narrative context far removed from that of both his alleged sources. 

For a source hypothesis is only as cogent as its ability to support a plausible explanation of all the alterations an author ostensibly would have made to the texts on which he was allegedly dependent.  

Luke obviously decided not to preserve Mark's formulation or use of the mustard seed parable. For Luke's own description of the growth of the mustard plant

•  differs in practically every detail from Mark's  &
•  is introduced five chapters after Luke had quit following the Markan discussion of Jesus'  teaching in parables.

Thus, the "dependence" of Luke's version of this parable on the text of Mark is far from obvious. True, there is a formal parallel between the pair of rhetorical questions about an appropriate analogy for the kingdom of God that introduce the mustard seed in both gospels.  But aside from their common reference to the "kingdom of God" the Lukan & Markan formulae are phrased quite differently. The level of verbal agreement between Luke's & Mark's versions of the mustard seed analogy is even lower. Thus, Luke's version of this parable is not even a paraphrase of Mark's. If Luke recalled the abstract rhetorical structure of a formula that Mark cites in a different context, why did he not recall or choose to use any of the details of description of the growth of the mustard seed stressed by Mark?

The fact that the phrases invoked by Luke to describe the mustard plant echo only insertions introduced in Matthew's alteration of the Markan parable makes Luke's failure to follow Mark all the more problematic. For Luke's version of the mustard seed analogy is more succinct than Matthew's precisely because it omits elements of the description that Matthew simply copied from Mark ("the smallest of seeds" becoming "the greatest of shrubs").  So, if Luke based his wording of this parable on the canonical text of the gospel of Matthew, then he must have used Mark's version as a negative filter, deliberately deleting most of the wording that Matthew & Mark had in common. Moreover, his opposition to the Markan presentation of this parable must have been so strong that he decided to transfer it (along with Matthew's non-Markan parable of the leaven) to a narrative context that had none of the catchword motifs found in either of the other synoptic gospels.  

Yet, Luke did not simply favor all of Matthew's alterations of Mark either.  For instead of echoing Matthew's single declarative statement introducing the mustard seed analogy, he chose rather to preface it with a pair of rhetorical questions -- a rhetorical strategy also used by Mark.  Thus, if one presupposes that Luke derived his material from Matthew as well as Mark, his version of the parable of the mustard seed seems to be a bizarre hybrid, a fragment of a Matthean parable, purged of Markan elements yet sporting a Markan preface, planted in a conceptual field totally unrelated to either alleged source.

If the only presumed sources for Luke's version of the parable of the mustard seed were the canonical gospels of Matthew & Mark, then Luke deliberately

• decided not to use it in the same narrative context where both Mark & Matthew recorded it,
• introduced it at a later point where it had no evident relevance to surrounding material his narrative,
• roughly paraphrased the rhetorical questions that introduced Mark's version of the parable yet
• chose not to repeat any detail of Mark's description of the growth of the mustard plant, but rather
• recalled Matthew's description of the mustard minus all phrasing that Matthew got from Mark, & then
• reproduced Matthew's parable of the leaven almost word for word, after paraphrasing its preface.

Such a puzzling picture of Luke's editorial activity is made more problematic by the observation that it does not follow Luke's normal redactional practice. Luke often paraphrases & condenses or omits Markan material & sometimes relocates a Markan passage to a logically preferable point in his narrative (see "Jesus' true kin"). Yet he usually keeps closer to Mark's verbal formulae rather than revisions introduced by Matthew (see "why parables"). Why would he have suddenly abandoned such an editorial strategy in the case of a parable where Matthew supports Mark's wording? 

Botanically, the common Markan & Matthean elements that are missing from Luke's description of the mustard plant (a "shrub" with bird "in its shade") are more accurate than the surrealistic details that he shares with Matthew (a "tree" with birds nesting "in its branches"). On the other hand, the scenarios of parables peculiar to Luke -- e.g., the Samaritan & Prodigal Son -- are quite realistic in detail. Luke regularly portrays Jesus as using parables as pedagogical examples. Thus, to imagine that he deleted credible naturalistic elements from an analogy designed to illustrate the kingdom of God which he found in two gospels & preserved only a fantastic image extracted from only one of them is to suggest that in this particular instance Luke was not only uncharacteristically capricious in revising his sources but pedagogically perverse. 

Finally, if Luke deliberately performed radical surgery on Matthew's version of the mustard seed parable to highlight its unrealistic details, why did he take over the mundane Matthean analogy of the leaven virtually verbatim? What plausible philosophical or aesthetic rationale could have prompted such editorial inconsistency on the part of Luke?  

The hypothesis that the extant canonical text of Matthew was Luke's direct source for the parables of the mustard seed & the leaven creates more puzzles than it solves. So, Farrer's solution to the synoptic problem is not as simple as it first seems. 

D	Are Matthew & Luke independent revisions of Mark & Q?

Any hypothesis which presupposes that the only sources available to the author of a synoptic gospel in the 1st c. CE were other canonical gospels that are still extant today is bound to have difficulty explaining the rationale for Luke's version of the parables of the mustard & leaven. For it must account for editorial decisions in Luke's alleged revision of the text of Matthew that border on the irrational.  The Two Source hypothesis offers a far simpler solution to the complex relationship of these synoptic parables by assuming 

• that Matthew & Luke probably had access to a source (Q) containing sayings of Jesus other than Mark & 
• that each independently added material from that source to the narrative framework provided by Mark.

Luke's lack of dependence on the text of Matthew is shown by the simple observation that he does not follow Matthew's presentation of the parables of the mustard & leaven.

Addition is always a simpler operation to explain than subtraction. In the case of this pericope, it is fairly obvious what material Matthew probably added to Mark.  Completely non-Markan elements that Matthew inserted are:

• the parable of the leaven &

• citation of Ps. 78:2.

Both are easily accounted for on the basis of strategies of composition that are characteristic of Matthew. For Matthew often traces a detail in the story of Jesus to fulfillment of some quotation from Jewish scripture that is not cited in other gospels (e.g. Isa 6:9 in his version of Jesus' rationale for using parables). He also frequently presents other sayings in a context where neither Mark nor Luke locate them (e.g., the paradox of the haves & have-nots, blessing of eyes that see, lamp & measure).

If one notes the web of catchwords & motifs common to Matthew & Mark, it is easy to understand why Matthew chose to insert the analogy of the leaven where he did.  Following Mark, Matthew

• presented three consecutive parables about seeds (sower, harvest & mustard),

• two of which (harvest & mustard) are introduced as analogies of the kingdom of Heaven ( = God) &

• two of which (sower & mustard) stress phenomenal growth.

The leaven is also explicitly identified as a parable about the kingdom of Heaven & the large volume of flour in which it is placed (about 30 pounds) implies phenomenal growth. Moreover, Mark's sharp contrast (echoed by Matthew) between the minute size of the mustard seed & the huge size of the full-grown plant provided a perfect memory link for recalling a similar contrast between the little leaven & the inflated volume of a lot of flour. 

The fact that parables of the mustard & leaven are recorded in tandem in the gospel of Matthew illustrates the natural tendency of the human mind to compose material by associating similar wording or images.  This is a common phenomenon that is no more characteristic of Matthew than of any one else.  Thus, the mere fact that Luke also links the parables of the mustard & leaven is not sufficient evidence to conclude that he derived this pairing directly from the canonical gospel of Matthew. 

The differences between Luke's version of these parables & Matthew's are extensive enough to make any claim that the latter is the direct source of the former questionable.

• The mustard & leaven are woven into the surrounding fabric of the gospel of Matthew by an intricate network of catchwords; the parallels in the gospel of Luke are not.
• Luke introduces both parables with rhetorical questions; Matthew does not.
• Matthew stresses the contrast between the small size of the mustard seed & the large size of the full-grown plant, Luke does not.
• Luke does not echo any of the narrative prose that Matthew uses to introduce either the mustard or the leaven.

The similarity between some of the wording in both versions of each parable is great enough to suggest some kind of dependence upon a common literary source. Yet it is hardly enough to prove that that text was the gospel of Matthew. 

It would be clear that Luke used Matthew only if it was certain that Matthew himself invented the parable of the leaven & the surrealistic changes to Mark's description of the growth of the mustard plant (a tree with birds nesting in its branches).  But that is hardly the case.  

Matthew repeatedly stresses that Jesus' teaching fulfilled the Torah & the Prophets. The Hebrew prophet Hosea, however, represented God as comparing the corruption of Israel's leaders to the rising of leavened dough:

Hosea 7
1	"When I would heal Israel
	the corruption of Ephraim is revealed,
	and the wicked deeds of Samaria;
	for they deal falsely
	the thief breaks in,
	and the bandits raid outside...
4	They are all adulterers;
	they are like a heated oven,
	whose baker does not need to stir the fire,
	from the kneading of dough
	until it is leavened."

Is it likely, then, that Matthew would have deliberately created an analogy for the kingdom of Heaven that focused on a profane process that Hebrew scripture used as a metaphor for moral corruption? 

If Matthew did not fabricate the parable of the leaven de novo, then he must have gotten it from some source that identified it as a saying of Jesus. Such a sayings source -- which could be called "Q" -- would presumably have been known by other early Christians than Matthew.  The parallels in Luke's presentation of the parables of the mustard seed & leaven support this conclusion, while the differences in Matthew & Luke's performances suggest that each author used this common sayings source independently.

• The pairing of the parables of mustard seed & leaven is a compositional feature that can be credited to Q.
• Likewise, the description of the mustard plant as a tree with birds nesting in its branches is traceable to Q.

The simplest explanation of the differences between the Matthean & Lukan presentation of parables of the mustard & leaven is that each author inserted this pair of Q sayings into his narrative framework without using the work of the other.

• Matthew wove Q's description of the mustard plant together with Mark's to produce the bizarre image of a plant that became both a shrub & a tree. Since Mark had no parable of the leaven, Matthew simply copied that parable from Q.
• Luke omitted Mark's version of the parable the mustard seed but later inserted this pair of Q parables in a context where he was not following the outline of Mark's narrative.

Since Luke did not try to integrate the mustard seed & leaven into Markan material, his version of these parables is probably rhetorically closer to the original wording of Q than is Matthew's grafted hybrid. Thus, the Two Source hypothesis is the one leading solution to the synoptic problem that does not require one to suppose that Luke performed elaborate inexplicable surgery on the text of the other synoptic gospels. Rather, it simply supposes that he respected the integrity of the Jesus sayings he copied from one source (Q) as much or even more than the material he got from another (Mark).