grammar
I'm wondering about usage of the word "save" when it's about saving a file (in a computer).
When we can't save a file, what do we say?
"The file doesn't save."
"The file isn't saving."
"The file isn't being saved."
I think that #3 is correct, but the word "save" can also be intransitive. I would like to know if I can use it in that way too (like #1 and #2).
The form, X is [number] times the size of Y always means X is [number] times bigger than Y.
The form, [number] times smaller is perfectly acceptable, clear (not ambiguous in any way), and is often more popular or even the only idiomatic form in common usage. I'll call this the Times Smaller Form. The preference (aka "popularity") for this usage (instead of the Fraction Form) grows as [number] gets bigger. This is demonstrated in the following Google Ngrams.
Google Ngram Three, Four
In these Ngrams, positive values means the Times Smaller Form is more popular and negative values means the Fraction Form is more popular. (See footnote #1 for an explanation of the Ngram equations.1) Note above that the only instance (in this Answer) where the Fraction Form is more popular than the Times Smaller Form is "one third the size". In all other cases (in this answer), the Times Smaller form is more popular.
Google Ngram Five, Ten
Note that these are at about 50%, which is higher than three and four.
Google Ngram One Hundred, One Thousand
Again, these are higher than the prior ngrams. +100% here means all instances are in the Times Smaller Form. The Fraction Form is non-idiomatic in this case.
Google Ngrams for Ten Thousand and One Million also show +100% of usage is in the Times Smaller Form indicating this is virtually an idiomatic form. On the other hand, it's grammatically correct to say "ABC is one ten-thousandth the size of XYZ". Interestingly, the Fraction Form doesn't strike me as odd or wrong in any way, but the searches in Google Ngram (and various corpora at http://corpus.byu.edu/) suggests this usage is rare.
Also note that the Times Smaller Form has even more usage than shown here since it has two variants for large numbers: a hundred times smaller, one hundred times smaller, a thousand times smaller, one thousand times smaller, etc. For example, it's natural to say "This is a thousand times smaller than that." See Google Ngram Variants
FOOTNOTE 1: Normalizing Google Ngram results.
In these Google Ngrams (A - B)/(A + B) shows a normalized difference from -1 to 1 (shown by Google Ngram as -100% to 100%).
A = Times Smaller Form, B = Fraction FormA, the Times Smaller Form) is more popular.A.) B, the Fraction Form) is more popular.B.).This method allows us to compare widely different result-counts on a common scale.
A=15, B=5. (15 - 5) / (15 + 5) = 10 / 20 = 50%. The difference 10 is 50% of the total 20.
Pair #2 is A=3000, B=1000
2000 is 50% of the total 4000.Even though Pair #2 is far more common than Pair #1, they both demonstrate that A is more popular than B, and in the same relative ratio. A potential weakness is that smaller result counts are less accurate. For example, A=3, B=1, also results in 50%, but this would be too small to be reliable.
Ironically, one of the things that makes learning English tense challenging is the fact we have fairly few forms. Also, the question "is this grammatical" is tough to answer for short utterances without context, as we can almost always come up with some scenario when a native speaker might say it and be understood by other native speakers without anyone noticing anything out of place. A better question is "Does this mean what I think it means" and "Is this what native speakers would say."
So with that in mind, let me actually answer the question you asked!
These two sentences are very similar, so it is not surprising that you would be confused. There is a subtle technical distinction, but the more important distinction is a difference in meaning, which I'll get to.
Grammatically this is fine by itself. I would take it to mean someone has asked you what would happen given some specific circumstances, e.g.:
a. "If I ran naked down the street, would someone call the authorities?"
b. "I'm sure that would happen."
Again, grammatically this is fine by itself. To me the most obvious context would be someone is asking you about your prediction of future events. E.g.:
a. "If I run naked down the street, will I be arrested?"
b. "I'm sure that will happen."
or, "What's the difference?"
I intentionally chose two examples that are very close together to make a point about agreement, not so much between verbs but between speakers: in the first example, person A says "If I RAN down the street". That "ran" is expressing a hypothetical circumstance (I believe it's technically known as "conditional II" because it's using a past tense verb to indicate something counterfactual). So it is only natural that person B would reply treating it as a hypothetical circumstance, too. Person A didn't say he was going to do it, he just wondered what would happen if he did.
In the second example, person A says "If I RUN down the street". This could still be hypothetical; in fact it probably is, since people don't usually run naked down the street. But because it's being phrased as an action that the person is actually contemplating, it seems a little more natural for person B to respond with "will". But note: "I'm sure that would happen" would also be a perfectly appropriate response.
In all the examples I used, everyone is still talking about things that haven't happened. By definition, then, these are "imagined events or situations" like it says in your grammar book. The difference is really based on how definite or how likely the imagined events seem to the speakers. Someone who says "I will" is implying that their imagined event is going to become reality, in a way that someone who says "I would" is not.
If you have a more detailed context, we can probably give you more definite advice to distinguish between the two.
For further reading, please see https://en.wikipedia.org/wiki/English_conditional_sentences which discusses a LOT of different possible uses of conditional in English (with sentence patterns).
Best Answer
The intransitive use of "save" is an example of an unaccusative verb, an intransitive where the agent is removed and the patient becomes the subject. There are many in English (eg "He cooks the food" -> "The food cooks").
The Oxford English Dictionary specifically lists this intransitive meaning (16 b.): "intr. Of data or a program: to be preserved by copying from main memory to a hard drive or other storage medium, allowing subsequent retrieval as required. Of a file or storage medium: to be replaced by a changed version residing in main memory." The first example given is from 1992: " If the file won't save, try saving it under a different name."
Thus all three of your examples are fine, according to the OED.