The gospel of Thomas has parallels to both synoptic parables. But unlike the canonical gospels the analogies of the mustard and the leaven are not paired as they were in the synoptic sayings source [Q]. Is their separation the result of secondary editing by the composer of this sayings collection? Or does it indicate that Thomas drew these parables from oral tradition in which they were not linked rather than from a canonical text? If the latter, then Thomas is evidence of the mechanics of orality rather than scribal plagiarism.

While both parables in Thomas are similar enough to their synoptic counterparts to reveal some kind of kinship, neither is close enough to prove parentage. 

Thomas’ parable of the mustard shares more common wording with synoptic versions. But its features do not consistently favor one gospel model more than another. 

• Like Mark and Luke (but unlike Matthew) it is introduced by a question. Yet unlike any synoptic version, the question is posed by the disciples rather than Jesus.
• Like Matthew (but unlike Mark and Luke) the analogy is to the kingdom “of heaven” (rather than “of God”).
• Like Matthew and Mark (but unlike Luke) the mustard is characterized as “the smallest of all seeds.”
• But unlike any synoptic gospel Thomas does not envision a human sower. Rather than being sown the seed “falls” on its own into the “prepared soil.” Thus the analogy is to an accident of nature rather than a deliberate product of agriculture. 
• Like Mark (but unlike Matthew and Luke) the germinated mustard “plant” is characterized as “large.” Yet it is not described as a “shrub” (as in Mark and Matthew) much less a “tree” (as in Matthew and Luke). Thomas’ characterization of mustard --- an annual herb rather than a perennial with a woody stalk -- is actually more accurate than any of the synoptics’ choice of nouns.
• While Thomas’ mustard plant provides (temporary) “shelter” for “birds of the air,” unlike all synoptic authors he does not describe these aerial vagabonds as “camping” in its shade, much less “nesting” in its branches.

 Thus, since

• Thomas’ performance of the parable of the mustard seed does not follow any synoptic model close enough to identify a particular canonical gospel as his script and
• his description of the mustard is closer to observation of nature than any of the synoptics,

it is simpler to conclude that he was recording from an oral tradition that was not only independent of but ostensibly older than any canonical narrative.

Not only is Thomas’ version of the parable of the leaven separated from that of the mustard by more than 75 pericopes, its wording resembles the synoptic parallels even less. While Matthew & Luke give near verbatim performances, Thomas’ rendition is better characterized as a variation on a familiar theme. By calling the kingdom “of the Father” it invokes a more domestic setting than either Matthew’s “of Heaven” or Luke’s “of God.” But its most striking divergence is that it draws an analogy between the paternal realm and a woman who took leaven rather than the leaven which was taken. Unlike the synoptic authors, Thomas does not specify the amount of flour in which the “little leaven” was buried. Instead of focusing attention on the organic activity of the hidden leaven itself, Thomas’ telling stresses the baker’s productivity in making “large loaves of bread.” Thus, it is evident that this version of the parable of the leaven is at best a distant cousin of the synoptic parallels and was not derived directly from any canonical text.

If the divergence of the Thomasine versions of these parables from the parallels preserved by synoptic authors is witness to the vagaries and fluidity of early oral Christian tradition, then it becomes all the more evident that the closely worded pairing of the mustard and the leaven in Matthew and Luke indicates their dependence on the same written source.