Is the Medieval French "the same language" as the modern French? It is French after all, right?
Is a 80 year old person the same person and with the same ideas, abilities, look, as when he was a 15 year old person? He has the same name after all.
Same language doesn't mean you can necessarily speak it without learning the new words, forgetting some stuff that went deprecated, learning some syntactic sugar and new features. If you were born in 1400 and lived to today, you'd be going from speaking from Medieval French to modern French with hardly noticing the difference...
Looks like Clinton was right saying that “it depends on what the meaning of ‘is’ is.”
Well, I think that's a reasonable analogy, except that with spoken language evolution, the unintelligibility tends to be mutual, whereas with Fortran there's substantial compatibility in one direction (i.e., GFortran will happily compile anything from f77 to Fortran 2008)
A modern C program doesn't compile in old C compilers. That doesn't mean it's not C. You can change tons of ergonomics and keep the language the same. Or you can keep the spirit the same (which in a language are its core semantics and concepts).
>I believe GP simply didn’t develop their argument effectively.
GP just casually said it's a whole new language in the casual, everyday sense, that a e.g. you can say "it's a brand new car now" after you redid the interior and did some repairs on your 10-year old car.
(And I got in with the Ship of Theseus thing to humor the objection -- not that I really consider the GP statement to have to be taken at face value).