The 10th and last round of negotiations between Iran and the six world powers was held in Vienna in a bid to strike a final deal. However, after the sides failed to agree on a final deal they decided to extend the negotiations until / by July 1, 2015.

In the original text the preposition until has been written. I am, however, wondering if we could use by instead, if so, is there any difference semantically?

Any help would be greatly appreciated

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    Delightful question. I hope a good answer will also address how the meanings change with negation: "They decided not to extend the negotiations until / by July 1, 2015"
    – Adam
    Feb 5, 2015 at 18:22
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    I didn't address your query about stative and dynamic verbs. The reason is, I don't think it makes any difference whether the verbs are stative and dynamic. I was just having a think about that before I wrote anything in my answer! But I am sure it doesn't make any difference! Feb 7, 2015 at 17:19

5 Answers 5


The time preposition by basically means before. So:

  • We need to finish the report by 5pm.


  • We need to finish the report before 5pm.

Until signifies the minimum duration of a situation or activity. So:

  • Stay in the office until 5pm

Means that the "staying in the office" situation should continue till 5pm. In other words the sentence means:

  • Only leave the office after 5pm.

The Original Poster's example:

Imagine that it takes some time to extend negotiations. Perhaps everybody needs to fill in many forms. There's a lot of administration to do, if you want to extend negotiations. Now look at this sentence:

They decided to extend the negotiations by July 1, 2015.

This sentence means that they decided to finish all the administration for the extension before July 1, 2015.

Now look at this sentence:

They decided to extend the negotiations until July 1, 2015.

This means that the minimum duration of the negotiations is from now to July 1, 2015. The negotiations will not finish till July 1, 2015.

Hope this is helpful!


The two prepositions are not interchangeable: to extend by indicates the additional length, but to extend until indicates the new limit.

"... extend the negotiations by another week ..."

"... extend the negotiations until the end of the month ..."

Hope that helps!


There is no reasonable situation where "by" would be an acceptable substitute for "until" in your example sentence. As others have pointed out, the only cases where you could use "by" are:

  1. They decided to extend the negotiations by (x), where x is an AMOUNT of time

  2. they expect to decide by (x) whether to extend negotiations where x is a DATE

Neither of these have the same meaning as your original sentence with "until". The second rendering above would mean that they have NOT yet agreed even as to how long to extend. (But your original sentence clearly indicated that they HAVE decided that question; i.e., they decided to extend the ending date of the negotiations to July 15.)

I suspect your puzzlement might not be with understanding how "by" and "until" work, but rather with understanding how "extend" and "postpone" work. To "extend" negotiations means to let them continue from now to a later date than expected. To "postpone" (or "suspend") negotiations means to stop negotiating now, but agree to "resume" at some future date.

They could agree to EXTEND, negotiations "until" (or "to") some date. This means negotiations will continue "until" then (they are expecting to finish "by" then.)

Or (and this is what I suspect you really meant) they could POSTPONE (or, more accurately, SUSPEND) negotiations "until" some date. This is the same as agreeing to stop negotiating now, and to RESUME talks "by" (on) that date. No ending date for the negotiations is implied.


They have decided to extend the negotiations until July 1, 2015.

They have decided to extend the negotiations by July 1, 2015.

When you use the preposition "until", it means "up to the time of". In other words, it expresses the continuity of an action. So the first sentence means that they have decided to extend the negotiations that may continue up to July 1, 2015.

On the other hand, you use the preposition "by" for a deadline to mean any time before a particular time, but not later than that. In other words, it's a one time action. So the second sentence means that they have decided to extend the negotiations any time before/at the deadline of July 1, 2015.


In my view two possiblities for the same idea. "Until/till" gives a time limit and "by + date" as well. The question remains how "by" can develop this special meaning. But the two words are not always interchangeable.

  1. The ticket is valid until March.

In 1 you can't use "by" which means "not later than /date + at the latest"

  1. The documents need to be ready by next Friday.

Here "until" would have the same meaning.

There is a somewhat different use of "by" in:

  1. By the end of the day we had sold 2000 tickets. (towards the end of the day)

and in:

  1. By the time we got home we were tired and hungry (When finally we got home).

By the way Longman DCE has 23 uses of by, preposition and 6 of by, adverb.

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