My question is not new. I just wanted to answer someone’s question about how to pronounce Thebes but I couldn’t find it after I signed up.
I had to look at several answers to explain this. I used to call it Theebs and so do most people and most posts advise that it is said that way but I used to work with a man from Egypt and he didn’t recognise what I was saying. He then said ‘Oh Tebeez’. No ‘Th’ as in ‘the’ just starting with ‘T’. I have since found some pronounciations the same as how he said it. I also read that this is probably the Greek way to say it. Greece occupied Egypt for some time and many things are named in Greek. If you can transfer my comment to the original question, that would be good but if you can’t, sorry for the extra question.
Th in Greek, and many other languages outside of English, represents an aspirated T. So the city in of Thebes in Greece and the one in Egypt both start with θ (theta) and not T (tau). That gets transliterated into English as th.
This is not a straightforward question, because you need to clarify which Thebes you’re talking about and the context for the discussion.
The ancient Egyptian city wasn’t even called Thebes — this was an external name imposed and used by the Greeks (kind of like how Germans call their country Deutschland but English speakers say “Germany” while French speakers say “l’Allemagne”). So if the question is about how to correctly pronounce the original local name of this place in a technical archeological discussion, it will have nothing to do with “Thebes.”
However, in a modern and casual discussion, the “theebz” pronounciation has been widely accepted and normalized in English, so as long as you accept descriptivism over prescriptivism, “theebz” is, let’s say, correct enough.
In between those two extremes, you have the modern Greek pronunciation, which (if I understand correctly) is in the neighborhood of “THEE-vuh” (as evolved from the ancient Greek “THEE-vai”).
So just say “theebz,” but don’t be surprised if an annoying pedant calls you on it (and be prepared to out-pedant them).
“Theebz” is clearly an acceptable exonym for a city whose name is pronounced differently in the original language. But that’s the point of an exonym: It‘s correct in the other language. Same reason why “Paris” is no pronounced the French way in English.
Theta is pronounced like an English th in Modern Greek, btw.