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 notes that an unbroken colt "might require the mother's presence to keep it calm amid shouting crowds" -- we know well enough how much 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 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.

A final consideration: Some suppose that Matthew includes the mother because he is extracting an inaccurate 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.

Objection: 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?

As Albright and Mann note, the whole purpose of the cloaks was to show honor to the rider. To use a modern comparison: If a dignitary rides to town in a limousine, and another vehicle follows, will what follows be a beat-up jalopy? Will it even be a limousine that looks bad compared to the first?

Of course not. By the same token the appearance of honor could only be maintained if BOTH animals were similarly accoutremented.

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.

World history is an enormous field with ranges of subjects over immense geographical and chronological ranges; knowledge of the Hebrew OT, in contrast, is a more focused discipline, especially for one like Matthew who shows clear knowledge of a variety of OT texts and rabbinical exegetical techniques.

To make this objection work, one would need comprehensive evaluations of Matthew's knowledge of the Hebrew text rather than pursuing generalities. Otherwise, it amounts to making an ad hoc exception simply to support a specific thesis.

The commentator Buchanan says that if the colt is so small it still needed its mother, it would not be a donkey that would be ridden at all.

How big and heavy were people at this time? The average height was no more than a little over 5 feet; on a diet that was significantly more sparse than ours, weights were probably similarly low. Without historical or experimental evidence regarding the carrying capacity of ancient donkeys over time, this assumption remains speculative.