It wasn't Mohammed who founded Islam.

[Rayaan]

Then what you need is to establish evidence that such a name was in use prior to islam. I know of no such evidence.

I have no evidence for that either, but that doesn't necessarily mean that "Muhammad" couldn't have been used as a proper name. There's no good reason to think why it can't be so, is there?

Muhammad's children were all given the same name, too, which shows that it was a proper name and not just assigned to Muhammad only:
Faṭimah bint Muḥammad
Ibrahim ibn Muhammad
Qasim ibn Muhammad
Zainab bint Muhammad
Umm Kulthum bint Muhammad
Ruqayyah bint Muhammad

So the name "Muhammad" has an honorary meaning and it was used as a proper name as well, such as the ones above.

I'm still not claiming that Mo is a prophet, so I'm still on the same side!

That wasn't what we were debating about, and you know that. I know you're not claiming that Muhammad is a prophet, but you claimed that his Prophethood was most likely attributed to him by someone else (unknown).

I keep presenting possible scenarios (maybe even contradicting ones), but none requiring any god talking to a man in a cave.

Again, same response as above. Don't think you're so sneaky and you can divert the argument now.

And if the source is, as I find often, someone already trustworthy by all or most? And if it was... dead? Like Mo himself was dead and some of his family took over the business.... and you then get some hadiths or parts of the qur'an where the reports of the claims of such relatives of Mo got recorded.
Would they question that source?
Kinda difficult, huh?

Then there has to be an explanation as to why it's more likely that some of his family would do that (i.e. attach a Prophetic role to Muhammad), as opposed to Muhammad himself claiming to be a Prophet.

"Command from on high" could be from Moses, from Jesus, from the previous leader of the tribe... who knows what he meant?!

But you yourself said that Sebeos is biased towards God, so what makes you think that the words "Command from on high" is more likely a reference to Moses or Jesus (or someone else) than God?

Very well.... do you think it likely that Mehmet was an actual prophet (even if only claiming to be so) instead of just a preacher of the law of Moses (as is well patent in Sebeos' account)?

Yes, and I do believe that he was an actual prophet. But, once again, that's not the issue that we've been discussing so far.

I was defending the view that Muhammad claimed himself to be a Prophet (which you said was possible), but you were defending the view that someone else claimed Muhammad to be a Prophet.

And if the latter view started off as a rumor, and no one knows how those start, as you said here:

If, on the other hand, we're dealing with a rumor, and who knows how those start, then it is far far easier for an individual to take it from rumor to fact, if that person is in a position of some power.

Then it's not possible for a person to take it from rumor to fact since he himself doesn't know whether the rumor is really true or not (before he turned it into 'fact').