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  • I've watched 10 movies until now.
  • He should have been here by now
  • I think in the first sentence, "by" doesn't work and using it will not be idiomatic. This applies to the using "until" in later sentence too. For me using "until" will not be be a correct usage. Instead the "until" in the first sentence and "by" in the second sentence fit the best. Am I right?
1

The difference is that 'by' refers to an event that happens at a moment in time, whereas 'until' refers to an event that happens for a period of time. They can't usually be used as alternatives of each other - except perhaps when used with negation.

Using your second example, to say "He should have been here by now" means that at some point in time, prior to this moment, he should have come here. To say "He should have been here until now" would mean that from some earlier time, continuing to this moment, the person should have stayed here.

To reply to your 3rd comment to whatever's answer, no, you cannot substitute by for until in all those examples. As mentioned, it doesn't mean the same thing, but in those cases it makes nonsensical sentences.

In the examples of: She won’t be back (by) 5 o’clock. - She won’t be back (until) five o’clock, they almost mean the same and can be substituted. This is the negation I was referring to. Technically, "She won’t be back (until) five o’clock" could mean that she will turn up at five o'clock on the dot, whereas "She won’t be back (by) 5 o’clock" means that time she will come back will be after 5 o'clock.

Edit for comments:

...whenever we have a negative sentence (negation conditions), (always) "by" and "until" work and mean the same?

Not always, and they're not exactly the same.

...She won’t be back (until) five o’clock

This means she won't be back before 5:00. Generally this means she will get back at 5:00 or some short time after.

I've watched 3 movies (until) now vs I've watched 3 movies (by) now

Either of these will work depending on context, but neither are really natural. If you were discussing the total number of movies you've ever seen, you might say: 'I'm going to a 5-movie marathon tonight. I've only watched 3 movies until now.' Alternatively, if you were explaining how long something took by comparison you could use the second example: Where has taken you so long? You were only supposed to be going to the snackbar for popcorn. I've watched 3 movies by now.' But in the first instance you are more likely to say 'I've only ever watched 3 movies' and in the second instance 'I've watched 3 movie since then'.

With 4) the inconsistency you see is because of the negation. "She won't be back by 5.00". At that point in time she won't be here. But after that point in time, for a continuous period she will be here. Similarly, "she won't be back until 5.00" says for the period of time from now til 5.00 she won't be here. After 5.00 (i.e., from that point in time) there is a likelihood that she will be here.

I think the negation trick is the only way to use them as alternatives to each other. I can best show this by example. Given the situation of a boss asking two employees about their previous workday. Firstly, positive:

"I was there by 5.00pm and I worked til midnight." vs "I was on the day shift and I was there until 5.00."

Then negative:

"I wasn't there by 5.00 because my bus didn't show up on time. But I was only a few minutes late." vs "I wasn't there until 5.00, because that's when my shift starts."

Now, there's no way the two sentences in the first example can mean the same thing. The two employees might have met in the staff room as one clocked off and the other clocked on, but they were doing two clearly different shifts.

The second example has a similar outcome, i.e., that at some time after five o'clock, both employees were at work, but the circumstances are somewhat different. In the first case '... was not there by...' means 'was there later than', in the second, '... was not there until ...' , means 'was there at'.

I hope this clears it up.

  • Thank you very much Mcalex. But first, do you mean that whenever we have a negative sentence (negation conditions), (always) "by" and "until" work and mean the same? Second, does "She won’t be back (until) five o’clock" mean "she will turn up (at) five o’clock sharp" only or it can mean "she will turn up (before) five o’clock" too? – A-friend Apr 14 '14 at 21:50
  • Third, according to what you mentioned ("'by' refers to an event that happens at a moment in time, whereas 'until' refers to an event that happens for a period of time."), using "by" in my following example is incorrect and only "until" will work in this sentence: • I've watched 3 movies (until) now. Because we are referring to a period of time, while "by" is used for a specific dot in time. Am I right? – A-friend Apr 14 '14 at 21:56
  • (4) You had mentioned: ("Technically, "She won’t be back (until) five o’clock" could mean that she will turn up ((at five o'clock on the dot)), whereas "She won’t be back (by) 5 o’clock" means that time she will come back will be ((after 5 o'clock.))"). I think this is inconsistent with what you had mentioned formerly: ("'by' refers to an event that happens at ((a)) moment in time, whereas 'until' refers to an event that happens for a ((period of time.))"). How do you justify them Mcalex? :-/ – A-friend Apr 14 '14 at 22:28
  • 5) I need to know whether only in negative form of the sentences we can interpret sentences in the way you mentioned above or in positive sentences we can interpret sentences in that way too? The problem is that if we can interpret them in that way in positive form of the sentences, we should believe that in all of my examples above (1-6) they both can work, but just using each one changes the meaning of its sentence. While I was thinking that in all positive (not negation condition) we are able to use only one of these two and therefor we have to choose the proper one based on the context. – A-friend Apr 14 '14 at 22:42
-1

You're right. It sounds natural and is grammatically correct.

Just the explanations are wrong. By and until are idiomatic for both sentences but require different tenses and/or continuous/simple form.

  • Thanks whatever, but I wonder if you could explain a little bit more. I mean why it's like that? – A-friend Apr 12 '14 at 21:23
  • The second one for sure is right, because "He should have been here until now." is absolutely wrong (wrong tense). The first one, however, I have placed in a context which can be changed, so it could be "I've watched 10 movies by now." With 'by', the first sentence means - My whole life (or in context specified time) I've watched only 10 movies. With 'until', the first sentence means - I've watched 10 movies all the way until now. Or more clearly (and more commonly) - I've BEEN watching 10 movies until now. So, I've been watching whole day these 10 movies, until now. – whatever Apr 12 '14 at 21:31
  • Do you mean using "until now" is more idiomatic, when it is used in Perfect Continuous tense and though it is not grammatically correct to use it in Perfect tense, but it is not a natural way to use it? – A-friend Apr 12 '14 at 21:42
  • So I won't be able to use "by" in even one of the following sentences as a substitution for "until": - I have been watching these 10 movies until now. - He’s been living in that apartment until today. - I had been working in that building until last week. Am I right? – A-friend Apr 12 '14 at 21:49
  • Hi there Could you please be kind enough to answer my questions bellow: -------------------- 1) In the following example of mine, is it possible to substitute "until" for "by" or not? - You must be home by7 o’clock. I guess until doesn't work here. ----------------------------------------- 2) Do the following examples mean the same thing? Are they all grammatically correct? Why you (hadn’t) come (until) 12 o’clock? Why you (hadn’t) come (by) 12 o’clock? Why you (didn’t) come (until) 12 o’clock? Why you (didn’t) come (by) 12 o’clock? – A-friend Apr 14 '14 at 5:47

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