Can it be done without a "Rosetta Stone"?

[Sam G]

I think it's important to make a distinction between whether it's the script that's unknown, the language that's unknown, or both.

In the case of Palmyrene, it sounds like the language itself was pretty close to other forms of Aramaic and the script was pretty similar to other Semitic scripts, so presumably it would have been cracked eventually even without a bilingual inscription.  Basically it would be the same as solving as a simple substitution cipher.

In the case of Linear B, it was mainly the script that was a mystery - the language was just an early form of Greek.  But because the script was a syllabary, the fact that it was written in Greek was not immediately obvious.  A lot of work had to be done on internal comparisons to establish which glyphs shared the same consonant but had a different vowel and vice versa before the identification of proper names in the text allowed researchers to assign sound values to the glyphs and read the text as Greek.

In the case of the VMS, the problem seems to be that the language is simply one that has not left any other known record.  The script is not completely understood either, but I think it's clear that it's an alphabetic script, and also certain things like the distinction between consonant and vowel seem mostly clear, and we could probably make reasonable guesses about some other things.  It's true that we don't know exactly which sound values to assign to the letters.  However, the structure of words and the rules governing how letters may be arranged in sequence to form words in the VMS are very distinctive.  Because these rules do not depend on the sound values assigned to the glyphs, we can simply look for the presence or absence of the same or similar rules in a given language to determine whether or not it can be the language in which the VMS is written.  There is certainly no known match, and I've personally checked many languages.  It certainly can't be any "major" language though obviously not every language in the world has been tried.  But my guess is that we don't have any other record of this language.

If it's the language that's unknown, then without a bilingual text I'm pretty sure it's never been done.  It's difficult to imagine how it could be done even in theory.  The best-known example where a language unrelated to any other has been deciphered is Sumerian, and that was done through bilingual texts.  So the question then becomes whether or not the illustrations can function as a bi-text of sorts, allowing us to infer the meanings of individual words and entire blocks of text based on context.  I'm guardedly optimistic that this is actually possible, and this is my main approach to trying to understand the text.