1

I think in the sentences below, “by” doesn't work and the only proper preposition is “until”, because all of these sentences are negative where “by” doesn't make any sense at all.

-A- She won’t be back until 5 o’clock.
-B- He will not return until Monday.
-C- Why didn't you come until 12 o’clock?
-D- I won’t be ready until Tuesday.
-E- I can’t be ready until 8 p.m.
-F- You mustn't be at home until 7 o’clock.

Whereas If we change the negative forms of these sentences to positive, we will see that "by" would be the proper preposition and then "until" would not work. Am I right?

5

This is a complicated question: it involves unstated implications and shifting ‘meanings’ which can only be sorted out by considering the aspect of the verbs involved.

First, the easy part.

Both by and until take as their object a point in time. I’ll call this Tterminal, because it is the endpoint of a timespan TS whose beginning is defined in your context. For instance:

She won’t be back until 5 o’clock. ... TS starts ‘now’, at the time of speaking.
Why didn’t you arrive until 12 o’clock? ... TS started (we may presume) at the point you started waiting for him.

Both by and until are used to locate an event in time. I’ll call this event E, and the time when it occurs TE.

The first important difference between by and until is that they signify different locations in time for E:

  • With by, it is asserted that TE occurs during TS: ... TETterminal.

    John will arrive by 5 o’clock. ... asserts that he will be at his destination at or before 5 o’clock.

    The negative asserts that TE does not occur during TS:...TE>Tterminal.

    John will not arrive by 5 o’clock. ... asserts that he will not be at his destination at 5 o’clock or at any time before that.

    Note that it is not asserted that he will arrive after 5 o’clock: he may never arrive.

  • With until, it is implied that TE occurs at the end of TS: ... TE=Tterminal.

    John will not arrive until 5 o’clock. ... implies he will be at his destination at 5 o'clock.

    Note, however, that his arrival at 5 o'clock is not an entailment, a necessary understanding. The only entailment here is that John will not arrive before 5 o'clock. His arrival at 5 o’clock is an implicature, an understanding which may be ‘cancelled’ or qualified by further specification:

    John will not arrive until 5 o'clock, maybe later.

And now the hard part:— Why is this permitted only in the negative? Why can you employ the positive with by but not with until?

okJohn will arrive by 5 o’clock.
John will arrive until 5 o’clock.

The answer lies in a consideration of verbal aspect—specifically, in the distinctive use of by and until with telic non-telic, and stative verbs.

  • Telic (‘goal’) verbs are those such as learn or arrive which have a change of state ‘built in’ to their meanings. Non-telic verbs are a) statives, which name states (know, be), and b) activities (run, sleep)—these do not change but just keep on going until they stop.

Here is the other important difference between by and until:

  • by marks E as a change of state within TS. When it is used with a telic verb, E is the culmination of that verb, the change of state it names:

    John will arrive by 5 o’clock. ... John’s journey will be complete at or before 5 o’clock.
    John will learn the results by 5 o’clock. ... *John

    When by is used with a nontelic verb, E marks the entry into the state named by that verb:

    John will know what to do by 5 o’clock. ... John will learn or figure out what to do at or before 5 o’clock.
    John will be here by 5 o’clock. ... John will arrive here at or before 5 o’clock.

    Note, however, that activity verbs resist this use. For instance, these uses would sound strange to most contemporary speakers:

    ? John will sleep by 5 o’clock.
    ? John will run by 5 o’clock.

    Our first inclination is to ‘recategorize’ sleep or run here in a telic sense: John will finish his allotted time of sleeping or running. To overcome this awkward sense, we cast the verb in the progressive mode, which recategorizes the verb as a stative:

    okJohn will be sleeping by 5 o’clock.
    okJohn will be running by 5 o’clock.

  • until marks E as the end of a state which persists throughout TS. With activity verbs this is straightforward:

    John will run until 5 o’clock. ... John’s state of running will end at 5 o’clock.
    John will sleep until 5 o’clock. ... John’s nap will end at 5 o’clock.

    Many stative verbs are uncomfortable with until, because we think of the states they signify as more or less permanent—know, love, like. Others like have and be, accommodate until when they are understood to signify temporary states:

    John will have this room until 5 o’clock. ... After 5 o’clock you may use the room. John will be busy until 5 o’clock. ...After 5 o’clock he will be free to see you.

    Telic verbs denote events, not states, so they usually do not work with until when used positively. The above example, for instance, John will arrive until 5 o’clock, only works if we can think of arrive as an activity, arriving repeatedly between now and 5 o’clock. That is extremely unlikely; but this would work:

    okJohn will arrive at 8 o'clock every morning until May.

    However, telic verbs can work with until when used negatively.

    okJohn will not arrive until 5 o’clock.

    This is because John is understood to be in a state of non-presence until he finally does arrive at 5 o’clock.


There are various sorts of telic verbs—accomplishment, achievement, semelfactive—but we won’t distinguish these.

  • Thank you very much @stoneyB. Accordingly do you confirm that the following sentences are wrong? - John will have this room (by) 5 o’clock. - John will be busy (by) 5 o’clock. - John will not arrive (by) 5 o’clock. – A-friend Apr 21 '14 at 6:59
  • @A-friend It depends on what you want to say. These say: 1.John will have this room starting at 5 o'clock, or earlier. 2. John will be busy starting at 5, or earlier. 3. John will not get here at 5 o'clock, or earlier. – StoneyB Apr 23 '14 at 1:30
5

In these cases, 'by' can be used but it changes what the speaker is expressing.

She won't be back until 5 o'clock.

expresses that Penelope will return at exactly 5 o'clock.

She won't be back by 5 o'clock

expresses that Penelope will return sometime after 5 o'clock. There is also an implication that something else will happen at 5 o'clock that Penelope will miss.

She won't be back until after 5 o'clock.

expresses that Penelope will return sometime after 5 o'clock, but nothing else is happening for Penelope to miss.

She will be back until 5 o'clock.

expresses that Penelope was away, then returned, is here now and will leave again at 5 o'clock.

She will be back by 5 o'clock.

expresses that Penelope will return sometime before 5 o'clock.

  • Thanks, but there is one more contradiction!!! One part of your statements is contrary to what @AdmiralAdama had mentioned: "-A- She will be back until 5 o’clock. - NO" – A-friend Apr 20 '14 at 17:04
  • It may seem like that, but "She will be back until 5 o'clock." makes perfect sense to a native speaker. It expresses that she was away, then returned (as in came back), and will leave again at 5 o'clock. – Johns-305 Apr 20 '14 at 19:17
  • (1) I need to say "she will be back at 5 o'clock or later than 5." What should I say: A- She won't be back until o'clock. B- She won't be back by o'clock. (2) I need to say "we will return on Monday or later." What should I say: A- We will not return until Monday. B- We will not return by Monday. (3) He came at 11 o'clock or even later. How should I ask him the reason? A- Why didn't you come until 11 o’clock? B- Why didn't you come by 11 o’clock? (4) I need to say I will be ready on Tuesday or even later. What should I say: A- I won’t be ready until Tuesday. B- I won’t be ready by Tuesday. – A-friend Apr 22 '14 at 10:56
  • (5) I need to say I will be ready at 8 o'clock or later. How should I say it: A- I can’t be ready until 8 p.m. B- I can’t be ready by 8 p.m. (6) I need to ask my roommate to be out by 7 PM. and come back at 7PM. or later. What should I say: A- Please don't be at home until 7 o’clock. B- Please don't be at home by 7 o’clock. I think in all cases the correct answer is 'A'. Do you agree with me? ------ I think in all of my questions above, only 'A' is correct and 'B' doesn't work at all. Do you confirm it? – A-friend Apr 22 '14 at 10:56
  • Sorry, these are pretty difficult to read. You should create a new thread where you can format for clarity. – Johns-305 Apr 22 '14 at 11:05
1

It's ok to use both "by" and "until" in negative sentences, but these two words have different meanings. "By" indicates a deadline (and includes the deadline) for some action and "until" indicates a period of time where something is true that ends at a specific point. They are similar but they are not the same.

Both "by" and "until" are combined with a time phrase that means a point in time, for example:

by 8pm
until 8pm
by Friday
until Friday

If I say "This test must be completed by 8pm", that means that the deadline is 8pm for this test. You can finish the test at 8pm or any point before 8pm. "By" always includes the deadline time. Notice that this indicates an action, usually very short, which is completing the test.

If I say "He is giving a presentation at the theater until 8pm", that means that I can hear him talk the whole period before 8pm, but not at 8pm. Notice that this indicates a state (something that is true or false) or an action over a period of time, for example the presentation. "Until" does not include the end time, because this is when the state stops.

The meaning of "He is giving a presentation at the theater by 8pm" would be different. It means that at some point before or at 8pm this person will give a presentation, but not all the time in this period before 8pm. "Until 8pm" means the whole period before 8pm. Conversely, you can't say "This test must be completed until 8pm" because completing a test is a short action and doesn't make sense for it to happen over a long period of time, which is what "until" implies.

Does this make sense?

[Edit - Adding some points that were elaborated in comments.]

  • Of course @AliumBritt. But I am sure "This test must be completed until 8 p.m." doesn't make any sense in English. Also "He is giving a presentation at the theater by 8 p.m." is not correct too. Right? – A-friend Apr 20 '14 at 12:34
  • 1
    @A-friend - The meaning of "He is giving a presentation by 8pm" would be different. It means that at some point before or at 8pm this person will give a presentation, but not all the time in this period before 8pm. "Until 8pm" means the whole period before 8pm. This is why you can't say "This test must be completed until 8pm" because completing a test is a short action and doesn't make sense for it to happen over a long period of time the way "until" implies. – Alium Britt Apr 20 '14 at 12:41
  • I exactly know what you are getting at @AliunBritt. But "completing a test" can be a process like "giving a presentation". If you can help me to distinguish these two, I guess it can be very helpful step to finalize this problem. – A-friend Apr 20 '14 at 12:48
  • 1
    @A-friend - You are confusing "completing a test" with "taking a test". Completing is only the finish of the test, which should be a short amount of time. Taking the test can be very long and that can be used with "until". Think of it like crossing the finish line in a race. The race takes a long time but crossing the finish line does not. – Alium Britt Apr 20 '14 at 12:51
  • Ahah. Got it. Excellent. It was the point I needed here. thanks a zillion @AliumBritt. ;) – A-friend Apr 20 '14 at 12:55
0

-A- She won’t be back until 5 o’clock. - YES

-B- He will not return until Monday. - YES

-C- Why didn't you come until 12 o’clock? - YES

-D- I won’t be ready until Tuesday. - YES

-E- I can’t be ready until 8 p.m. - YES

-F- You mustn't be at home until 7 o’clock. - YES

-G- I don't need the apartment to myself until 8PM. - YES

These all look good. However you can replace "until" with "by" in some of these and get a meaningful, grammatically correct sentence.

-A- She won’t be back by 5 o’clock. - YES

-B- He will not return by Monday. - MAYBE

-C- Why didn't you come by 12 o’clock? - MAYBE

-D- I won’t be ready by Tuesday. - MAYBE

-E- I can’t be ready by 8 p.m. - YES

-F- You must not be at home by 7 o’clock. - NO

-G- I don't need the apartment to myself by 8PM. - MAYBE

"By" and "until" have different meanings here. If the time in question is 5PM, "by 5PM" means 1PM, 2PM, 3PM, 4PM, and 5PM. "Until 5PM" means 5PM, 6PM, 7PM, 8PM, etc. This is why you can change "until" to "by" in some of these sentences and they still make sense. Not all of them... the ones marked MAYBE seem a bit illogical if you use "by", and the one marked NO is a negative command so you cannot use "by". But the ones marked "yes" can definitely be changed. They just have a different meaning.

Now let's take a look at the positive forms of these sentences...

-A- She will be back by 5 o’clock. - YES

-B- He will return by Monday. - MAYBE

-C- Why did you come by 12 o’clock? - NO

-D- I will be ready by Tuesday. - MAYBE

-E- I can be ready by 8 p.m. - YES

-F- You must be at home by 7 o’clock. - YES

-G- I need the apartment to myself by 8PM. - YES

Some of the sentences above would sound much better with a preposition that is neither "until" nor "by". You want to turn them into statements of fact rather than using periods of time.

-A- She will be back at 5 o’clock. - YES

-B- He will return on Monday. - YES

-C- Why did you come at 12 o’clock? - YES

-D- I will be ready on Tuesday. - YES

-E- I can be ready at 8 p.m. - YES

-F- You must be home at 7 o’clock. - YES

-G- I need the apartment to myself at 8PM. - YES

Finally, let's take a look at some positive sentences used with the preposition "until".

-A- She will be back until 5 o’clock. - NO

-B- He will return until Monday. - NO

-C- Why did you come until 12 o’clock? - NO

-D- I will be ready until Tuesday. - NO

-E- I can be ready until 8 p.m. - NO

-F- You must be at home until 7 o’clock. - NO

-G- I need the apartment to myself until 8PM. - YES

Most of these constructions are not allowed, but as you can see -G- is an exception.

This is a complicated subject and I do not have the grammar rules memorized. Hopefully these examples are helpful, and somebody else who knows the grammar rules can also post an answer.

  • 1
    Thanks a million because of this effort of you to help me to realize my needed point. I really appreciate this concern of you. Just another American Native had told me, "You mustn't be at home until 7 o’clock." is a completely unnatural sentence in English language. These types of contradictory remarks are causing me to doubt about this topic. – A-friend Apr 20 '14 at 12:31
  • 1
    I cannot concur in your last set: any of these is possible. Just for instance: "She will be back until 5 o'clock, but then she's leaving again." "You must be at home until 7 o'clock; after that you're free to leave." – StoneyB Apr 20 '14 at 12:41
  • 1
    No. Be back may designate a change of state OR a state. "She came back this morning. She will be back [i.e. will continue to be back] until 5 o'clock, and then she's leaving again." – StoneyB Apr 20 '14 at 12:48
  • 2
    @A-friend "Duuuuude! My girl is coming over tonight. I need the apartment to myself until 8PM. Don't come back until after 8PM." Hmmmm. Affirmative + "until". This works. Looks like the pattern is broken. Maybe we should add "I need the apartment to myself until 8PM." to the question as -G-? – AdmiralAdama Apr 20 '14 at 12:52
  • 1
    @A-friend - Both of those are correct, because "be at home" is a state. – Alium Britt Apr 20 '14 at 13:05

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