Greek/ilion & ilios
Having never seen a text of the Iliad in Greek, I'm confused over why the authentic name of "Troy" (never the Latin "Ilium") is expressed in the two ways: "Ilion" and "Ilios."
Did Homer himself use, in the actual Greek, one or the other, or both; and if both, did he use one form much more than the other; and again, if he did that, can you suggest to me your thoughts on why he might have done so? Do the two terms perhaps reflect merely different forms of speech? Is one perhaps the formal and the other less so, like a "nickname?"
thank you for your question. Homer uses the version "Ilion" a hundred times or so, whereas "Ilios" no more than ten. The city was named after its founder Ilus, of whom we know through a mythological tradition that has survived. So, Ilios (as a feminine noun) means "belonging/referring to Ilus". Same does Ilion, which is just another grammatical instance of the word. I wouldn't say it is a different speech or dialect, but it rather shows in how many ways one can form words in Greek or - depending on which version prevailed among speakers - that Ilion was the famous version of the time. It is a denominal adjective that is used as a noun and it could, theoretically, occur in all three genders with all possible endings. The interesting part is not in these, though, but in the co-existence of the name "Troia".
"Troia" derives from the pre-existent form "Troas", which is the name of the land that was reigned by Tros, great-grandson of Zeus - according to the same tradition - and father of Ilus. The city of Troia or Ilion was founded later. We can take for granted, that a land's or a wider region's name is principally older than a city's. I am afraid that I cannot tell for sure why both versions survived, but an assumption would be that at the time that the Iliad was orally composed, there must have been a preference to "Ilion" as most common town-name to refer to, even if "Ilios" sounds to me more "correct", as it is feminine and matches better the common town gender. Apart from that, Ilion could also be a "vernacular" version, let's say, as the neutral article as second occurence to an existing noun also makes it more "cute, canty and sweet", so as to match the loss of and to praise the "sweet and beloved Ilion".
Finally, I just wanted to mention that archaeological evidence has proved that the city/settlement where Ilion used to be, had already been inhabited for at least 1500 years before Homer's Troia. This is contradictory to the mythological tradition regarding what name occurred first against what name survived in the tradition (i.e. Troia vs Ilion). And it would be an interesting topic to research :)
Hope I answered some of your questions.