Btw, here's Morris's response to my comment:
"Amusing thought! For this to be credible, we’d need evidence that the word, or something very like it, was used in that milieu before the conquests; I don’t believe that’s the case. Anyway, we don’t have to posit such outside influence, because we’ve a paradigm right now that makes good sense of the evidence. Thanks for reading; I’m so glad you enjoyed it."
The more I've thought about it, however, the more the spelling issue bothers me. Why? Because clearly there was a tradition of Syriac and Pahlavi orthography, predating any of the Arabic texts we have, which spelled the name with an emphatic t rather than a non-emphatic d. Think of it this way: When the first coins mention Muhammad, and some of them are combinations of Pahlavi and Arabic, why is the Pahlavi still "mhmt" while the Arabic is "mhmd"? This is inconceivable unless there is an older tradition of writing the name in Pahlavi as mhmt; if a scribe were starting anew, or was not constrained by a pre-existing strong orthographic tradition, he would've written the same letters in both Aramaic-derived scripts (Pahlavi/Arabic).
So one must explain why there was such an orthographic convention, which seems consistently and broadly reflected in all of the earliest sources across a variety of languages and scripts (Syriac, Pahlavi, Armenian). Calling this widespread "variant spelling" does not resolve the problem for me, for reasons akin to those that Al-Jallad capably states while blasting the idea that Qur'anic orthography did not reflect actual pronunciation differences from later Classical Arabic: "One cannot explain this y as a mater lectionis for ā by appealing to Arabic orthography. We have no reason to believe that this was simply an orthographic convention at this early stage; indeed, orthographic conventions are almost always rooted in an older stage of pronunciation." (p. 37 n. 116).
http://www.academia.edu/7583140/Graeco-Arabica_I_the_southern_LevantLikewise, it seems to me that one must explain how this emphatic t orthographic convention arose and persisted so long and widely. Morris rightly argues that it is common for names to be spelled differently in different languages, but that is exactly the point: We can give good explanations for why the name "Ian" might be spelled differently in different languages. But if we found that name spelled "Ied" in German, we would require a good explanation as to how that can possibly have happened -- orthographic shifts and conventions have explanations behind them, they are not generally random. For example, we can readily explain why "l" and "r" might be mixed up in a Japanese Romaji transliteration of a name. But the very fact of this explanation reflects a deep linguistic difference; if you just said "Lobelatu" is a variant Romaji spelling of "Robert," the source of that variation can be explained as a product of linguistic differences.
Now, "Muhammad" in the Classical Arabic reading is based on a well-known shared Semitic triliteral stem 'hmd' that exists in many other Semitic languages (albeit rather strangely not in Syriac itself). So the original Arabic pronunciation reflected in the Qur'an must surely have reflected the non-emphatic 'd' pronunciation. There can be little question that 'mhmd' reflects some sort of older Arabic terminology. But then why the switch, and why are the earliest texts mhmt? I don't know. I'd be curious what a Semiticist like Al-Jallad would say on this subject.
This ties into the rather mysterious nature of the term "mhmd" itself. Gabriel Said Reynolds gives a good discussion of the issue in his book on the Qur'an's biblical subtext, concluding (I think rightly) that it was likely an epithet of some sort. What kind of epithet? To my mind, Christological, with Mohammed viewing himself as marching on Jerusalem like a second Jesus, whose Qur'anic descriptions are terminologically parallel to the few explicit uses of the term mhmd. I will be interested to see what is argued along those lines by Carlos Segovia, who seems to be on the verge of publishing several articles and books on the subject.
https://www.academia.edu/3372907/A_Messianic_Controversy_Behind_the_Making_of_Mu%E1%B8%A5ammad_as_the_Last_Prophet_2015_Upcoming_Conference_PaperAnother puzzling fact about our original source here. Thomas the Presbyter was evidently writing from within Syria itself around 640, which at the time was already overrun (according to him) by Arabs. So why would he get the spelling wrong (and it is in fact wrong to use emphatic t, unless there were variant pronunciations circulating at the time, in which case one would need an explanation of that)? It's not like the Arabs were aliens, they had been controlling his area for years. A further puzzling fact. Around 640 AD, Thomas writes about how in 634 the "tayyaye d-mhmt" attacked the Byzantines in Palestine. But when he earlier writes about the Arabs attacking and taking over Syria in 636/37, he does not refer to those Arabs as the "tayyaye d-mhmt," just as Arabs. This suggests that the tayyaye d-mhmt were seen as a Palestine-centered subgroup of the overall tayyaye conquest, which it seems to me is probably correct. Thomas was probably writing from a Syria controlled by tayyaye who did not see themselves as part of the earlier mhmt movement in Palestine -- a comparatively narrow Palestine movement which (following Shoemaker) ended in somewhat ignominious failure when their prophet-leader died and the apocalypse no came. It would take decades before that failure became steadily transformed into new narratives with wider significance, a la Early Christianity.
Topic: Misspelling Muhammad - Why Robert Spencer is wrong about Thomas Presbyter