This article was actually posted on Farrell Till’s II Errancy Discussion List. I have reformatted it for inclusion on my site. John Kesler’s commentary will follow his name, the material to which he is responding from Turkel will follow Turkel’s name.

TURKEL (http://www.tektonics.org/qt/twodonkeys.html)

Matthew 21:7 And brought the ass, and the colt, and put on them their clothes, and they set him thereon.

Matthew's variation from the other Gospels on this point raises two questions -- was there one donkey or two, and did Jesus ride one or two? Strictly speaking, one could point out for the first question that there is no technical, logical contradiction, since the other Gospels do not say there was only the colt there -- they merely don't bother mentioning the mother. Yet her presence is likely in this context, even if it is not mentioned. Keener [Matthew commentary, 491] notes that an unbroken colt
"might require the mother's presence to keep it calm amid shouting crowds" -- we know well enough from American rodeos what chaos an unbroken animal might cause. Then comes the question, Is Jesus riding on both donkeys? The question may be varied to say, was Jesus riding them in alteration, or (if the skeptic has a sense of humor) on both at once -- maybe one on top of the other? Not really -- this is just an amusing grammatical ambiguity; the "them" on which Jesus sat could refer back to the
clothes, not the animals.

KESLER
Turkel's "solution" is probably the most common one offered-that "them" refers to the clothes, not the animals. This may seem plausible until we analyze Matthew 21:7 more closely: "they {Jesus' disciples} brought the donkey and the colt, AND PUT THEIR CLOAKS ON THEM {donkey and colt}, and he sat on them." If Jesus actually was only going to ride one animal and the second creature was simply a "mother's presence" to calm the ridden beast, why would the disciples put cloaks on both animals? Also, a comparison with the other synoptic accounts lends credence to the belief that Matthew meant that both animals were ridden. I will put Mark, Luke, and Matthew's versions next to each other for easy comparison.

Mark 11:7 Then they brought the colt to Jesus and threw their cloaks on it; and he sat on it.

Luke 19:35 Then they brought it to Jesus; and after throwing their cloaks on the colt, they set Jesus on it.

Matthew 21:7 they brought the donkey and the colt, and put their cloaks on them, and he sat on them.

Mark and Luke clearly say that Jesus sat on IT, the colt, even though both gospels, like Matthew, make mention of cloaks, plural. And even if it is allowed for argument's sake that "them" refers to the cloaks, how could Jesus, by riding one animal, sit on cloaks that were placed on two separate animals?

TURKEL CONTINUES:
A final consideration: Some suppose that Matthew includes momma because he is wrenching out a bad meaning from Zech. 9:9: "...riding upon an ass, and upon a colt the foal of an ass." This is unlikely. The Hebrew of Zech. 9:9 renders the "ass" in the male gender -- and Matthew's knowledge of the Hebrew text elsewhere shows that he knew this was the case [ibid.]. (For
more on harmonizing, see here: http://www.tektonics.org/harmonize/demoniactale.html)

KESLER
This is a blatant example of begging the question of Matthew's accuracy. Even conceding that Matthew shows "knowledge of the Hebrew text elsewhere," this is not proof that an error wasn't made in Matthew 21. A historian may demonstrate great knowledge of world history, but this would not preclude that person's making a historical error. Every alleged error needs to be considered and judged on its own merits, regardless of one's accuracy in other matters. Farrell Till also address this colt/donkey issue here, http://www.infidels.org/library/modern/farrell_till/prophecy.html and points out that Matthew is the only synoptic gospel writer who alleged that the "triumphal entry" fulfilled Zechariah 9:9, making it likely that Matthew would try to force fit Jesus' donkey ride to Zechariah's prophecy. The URL that Turkel provides makes the usual "if there were two (animals, angels, demoniacs, etc), then there had to be at least one" argument which is also addressed in Till's article. Matthew thought that two animals were intended, so he was going to make Jesus ride two animals no matter how silly the outcome.