The ambiguous "until"

As a non-native English speaker, It seems to me that the word "until" is quite ambiguous. It's been told that when it's used with a date it includes the date. (Does "until [date]" mean "before that date"?)

But it's still unclear to me.

"X will be there until the 11th." When will X leave? On the 12th, right?

"X won't be there until the 11th." When will X be there? On the 11th, right?

If so, can anyone explain why it differs? Does it depend on whether it's negative and positive?

And how about other periods of time, like high school.

"X hasn't done it until high school" In this case X did it at some time during high school, right?

"X has been doing it until high school" In this case it seems to be unclear when X stopped. During high school or before starting high school.

Then with an attempt of clarification:

"X has been doing it until he entered high school" Does it mean X stopped doing it before or just after he entered high school? Or could it be both?

Is this clear to native speakers or is it just me?

Edit: Seems like a lot of my confusion was made by this answer. http://answers.yahoo.com/question/index?qid=20130205142054AAIqP06

Solution 1:

"X will be there until the 11th." When will X leave? On the 12th, right?

X would leave on the 11th.

"X won't be there until the 11th." When will X be there? On the 11th, right?

Yes, they would arrive on the 11th.

"X hasn't done it until high school" In this case X did it at some time during high school, right?

Yes, it means that X did something for the first time when they were in high school.

"X has been doing it until high school" In this case it seems to be unclear when X stopped. During high school or before starting high school.

To me, it clearly means that X stopped doing something when they started high school.

Then with an attempt of clarification:

"X has been doing it until he entered high school" Does it mean X stopped doing it before or just after he entered high school? Or could it be both?

It means that X stopped doing something when he entered high school. Writing it this way is a possibility but, not really necessary. It was expressed sufficiently with the previous quote.

Is this clear to native speakers or is it just me?

That is clear and sentences that use the word until, like that, are used regularly by native speakers.

Solution 2:

You are right in that there is (sometimes) ambiguity in the meaning.

Some expressions have one possible interpretation:

"I (had) never played squash until / before I went to university" is clear enough - I played squash only after going up (if at all, but this would be a quirky take).

They do not have to be negative statements:

"We played squash until 1 pm" is non-negative but still unambiguous.

It's when the time reference itself is imprecise that possible ambiguity arises.

"John will be there until the 11th." What time on the 11th? The exact moment the day starts? (unlikely). We use this sort of expression rather loosely to indicate that you may or may not find him there if you go looking for him at some time on the 11th. He may leave at the start of the day, in which case you'd miss him; he may leave at noon, in which case you might catch him. You're only really sure to catch him on the 10th (9th, 8th...) (and assuming he's not at the cinema etc, of course).

With negative statements, it's clearer:

"John won't be there until the 11th." You won't catch him on the 10th, 9th... But you've a chance on the 11th. More so later in the day.

'Up to and including' and 'until and including' are widely used to show that the end-point of the interval in question is meant to be included, but with a 'wide end-point' (like 'the 11th', a certain amount of uncertainty is bound to remain.

Solution 3:

Until generally means up to this point. It is unabmiguous when the point referred to is an exact demarcation.

I am here until 2PM (at 1:59:59 I am still here; at 2:00:01 I am gone)

When referring to a condition or state of affairs that has a duration, it suggests the change will occur at or near the start of the duration

I am staying away until he is gone (I will return immediately upon his departure, or soon thereafter)

It is especially ambiguous when used with a time specific reference that has a significant duration

I will be there until Thursday (leaving at minute after midnight Thursday morning? at noon? by 11:59 PM?)

This last example might even mean

I am there through Wednesday, but will be elsewhere on Thursday

Context often helps. When used with a negative, and refering to a period with a duration, it often means the start of that duration.

I will not be back until Thursday (I will be back on Thursday, probably all day, although exactly when is not clear)

Solution 4:

I think it's fair to say that until always indicates the end of a period of time, but:

It will happen until ... is specifying the end of a 'positive' period of time, i.e. the event will continue until the specified date (or period), and presumably then finish.
Hence a positive until is indicating the end of the event in referred to.
E.g. The season continues until the end of September means The season finishes on or about 30th September.
Analogous to Edwin's example: I swam regularly until I went to university means I stopped swimming regularly when I went to university: it didn't happen while I was at university.

It will not happen until ... is specifying the end of a 'negative' period of time, i.e. the event will continue to 'not happen' until the specified date (or period), and presumably then start happening.
So a negative until is in fact indicating the start of the event referred to, i.e. the start of the positive period.
E.g. The season doesn't start until the beginning of June means The season starts on or about 1st June.
To borrow Edwin's example: I had never played squash until I went to university means I started playing squash while at university: it did happen while I was at university.

Whether the period in question is inclusive or exclusive of the mentioned date is often ambiguous, but may be apparent from the context. I offer the following as 'general guidance' (but certainly not to be relied upon when the actual date is critical to you):

A positive until normally includes the specified date (or period).
E.g. The show is on until 28th June would usually mean that 28th June is the last night on which you can see the show.
Thus, the 'positive' period includes the date.

A negative until normally excludes the specified date (or period).
E.g. The show is not on until 28th June would usually mean that 28th June is the first night on which you can see the show.
Thus, the 'negative' period excludes the date, and hence the immediately following 'positive' period necessarily includes the date.

In both cases, the event you are actually interested in, namely "the show" is inclusive of both dates.

As Edwin has indicated, where the time of day is more critical, as in He is / isn't here until ..., there is an ambiguity as to the precise time, but normally both dates would be inclusive of the period that he is here.

He is not here until the 11th = He arrives on the 11th.
He is here until the 15th = He departs on the 15th.
Thus, his period here includes (at least part of) both days.