Do "finché" (and "fino a che") mean "until" or "as long as" (or both)?

Question

I know we're not supposed to ask questions that can be looked up in a dictionary here, but I have already looked up dictionaries, read blog posts and forum discussions, all of which have just confused me even more. So I just hope someone can clarify this for me. Please bear with me as I try to explain where exactly my confusion is.

First, I want to point something out. The expressions as long as and until, with regards to time, are both ways to specify the time period during which an event occurs with respect to another event. Other than this, they are complements (or negations) of each other. Since when I say A as long as B, I'm implying that the time of A intersects with the time of B. But when I say A until B I'm implying that the time of A does not intersect the time of B.

According to this blog post, finché just means as long as, and finché non means until, which would make perfect sense given what I mentioned above. In fact, I don't see the point of having a separate definition for finché non when that can be deduced from the definition of finché. That post also mentions that finché is sometimes, mistakenly used to mean until (but I guess finché non is never used to mean as long as). I even checked some translations of finché using reverso context and I see that it's in fact used both ways. But if I trust the blog post above, most of these Italian writers are just using it wrong (or colloquially).

That seemed good enough, but then I remembered the expression fino a che. I read somewhere that finché is just a shorter way to say fino a che. But when I translate this in Google, it says until. That's finché non, it's negation. So then I looked up fino a che on reverso context and saw that it's also used both ways!

Speri fino a che il tuo avversario si stanchi. = You wait until your opponent tires.

but also

Lo sarò fino a che potrò. = I'll be one for as long as I can.

So either these Italian writers are also using it wrong, or the blog post above is wrong. I'm starting to believe that both finché and fino a che can actually (and correctly) mean both as long as and until, and the only way to tell one from another is by looking at the context. My current understanding is that A finché B means A until B if B is an instantaneous event, like that start or end of something. And it means as A long as B when B is something that happen over a period of time.

So I guess to summarize, my questions are:

1. Can I use finché every time I'd use fino a che?
2. Can I use fino a che every time I'd use finché?
3. Is the blog post I mentioned correct in that finché only means as long as although it is sometimes mistakenly used to mean until?
4. If the answer to the above question is no, then is my current understanding of how to tell one meaning from another any good?

Answer 1

Treccani dictionary defines finché as:

Fino a che, fino a tanto che, fino a quando; indica il perdurare di una cosa o di un fatto per tutto il tempo in cui dura un’altra cosa o un altro fatto o non se ne verifica uno nuovo; generalmente usato con il modo indic.: f. c’è vita c’è speranza; restate f. volete; gridò fin che ebbe fiato in corpo; E tu onore di pianti, Ettore, avrai ... f. il Sole Risplenderà su le sciagure umane (Foscolo). In frasi negative indica invece che una cosa non può o non deve accadere fino al momento in cui non se ne verifica un’altra: non ti muovere f. non lo dico io; non aprì f. non l’ebbe riconosciuto.

So, it seems to confirm that finché would correspond to “as long as” (the contemporaneity of two actions of situations), while finché non would correspond to “until” (one successive to the other ones), and this is the traditional view.

However, other dictionaries adopt a somewhat more modern (and realistic) approach. De Mauro's dictionary, for instance, admits both uses of finché, and even says (my translation): “the adverb non may or may not be present, while the meaning does not change”:

fino a quando, fino al momento in cui, in proposizioni temporali all’indicativo o al congiuntivo in cui può essere presente o meno l’avv. non senza che il significato cambi: aspetterò qui finché non torni, finché andavano a scuola erano buoni amici, puoi stare con noi finché vorrai; fino al punto in cui: siamo andati avanti finché la strada si è interrotta

The more traditional, and quite authoritative, Grande Dizionario della Lingua Italiana also includes both meanings. You can see the complete article, but just to give two examples from good writers:

“as long as”: Finché hai dardi, scàgliali! (D'Annunzio)

“until”: Rimase a guardare ritto finché la luce disparve. (Comisso)

So, context is actually the only guide.

As for possible differences between finché and fino a che, as an Italian I don't find any, besides the exigences of a sentence's euphony. More to the point, dictionaries seem to agree in treating both the one-word form and the split form together: Treccani and GDLI (above) define finché as “Fino a che [and so on]”; furthermore, Treccani, in its article about fino, puts together “fino a che o fin che o finché”; see also “Finché or fin che?”.