What's the big contradiction?

A language can still be a thing after decades while looking very different.

Ever heard of the Ship of Theseus?

I understood the Ship of Theseus to have been rebuilt with new materials, not with a new design. I suppose the interpretation is somewhat flexible but I don’t think it quite applies to this case. If a modern program doesn’t compile on an older version, I would interpret that as being a significant change in the language, the referent of “FORTRAN”. I believe GP simply didn’t develop their argument effectively. 1970’s Camaros aren’t interchangeable with 2010’s. To the public they are both Camaros, but to a mechanic they are very different.

>If a modern program doesn’t compile on an older version, I would interpret that as being a significant change in the language, the referent of “FORTRAN”.

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).

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)

Sure, from the general public standpoint, by the sound of it, Fortran is still a thing...

That would suggest that, for example, C11 should not be referred to as the C programming language, since it introduces some new features? Similarly, if I said “I have a Camaro” to you, would you expect that I have a 1970s car or something more recent?

C11 still looks like (and still is) C, despite the new features. In contrast, to say that the new Fortran is the same 'thing' as the old Fortran is disingenuous. For example, the old Fortran did not support recursion (which fact I consider a feature rather than a "bug").

ANSI C looks pretty different to K&R C, especially in the function declaration syntax. The only difference is Fortran had its facelift just a little later.

>For example, the old Fortran did not support recursion (which fact I consider a feature rather than a "bug").

So? C# 1.0 didn't support 90% of the cool features of C# whatever it is now, not even LINQ, the bread and butter of C# programmers.

Java up to 1.4 didn't have generics, closures, streams, modules, and tons of other stuff besides. Soon it will be getting many more.

Is it a different language for that?

On the other hand, C was given a different name when classes were added to it.

Thing is, adding and/or removing features may have an impact on the implementation, can potentially introduce subtle changes to the semantics of the existing constructs and therefore their behavior at run time, have general performance implications (e.g. due to a change in what optimizations are possible), etc. Is it "the same language"? Not quite. It is a "super-language," at best. If it's 100% backwards compatible, that is (which is not guaranteed).