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Hi there,

Please I looked for the use of unless but I didn't find when NOT to use it .

1)Unless is used here.. I'll be back tomorrow unless there's A plane strike.

2) it's written that unless can't be used but I actually don't know why.

I'll be glad if she doesn't come this evening.

Could you please explain when NOT to use it, thanks A million

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"X unless Y" usually implies that X is the normal/default/expected case, that will occur provided Y does not intervene to prevent it. In the "I'll be glad" sentence, being glad is not something that will occur as a default unless prevented: it will occur only in the specific case that she does not come.

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مسك الياسمينwhen NOT to use it.

There may be other reasons not to use "unless", but this idea explains the example you quoted. Generally speaking you don't use "unless" after "will be" plus an adjective that describes how someone's feelings will be affected if something happens.

1) I will be glad if she doesn't come this evening. OK.
2) I will be glad unless she comes this evening. No.

2) is the rephrasing of 1) using 'unless' instead of 'if', but it doesn't work in this context.


Similarly, we don't use 'be worried unless', 'be sad unless', 'be surprised unless' as in the following.

Tom's mother will be worried unless he is home by midnight. No.
Martha will be sad unless she gets a letter from Fred. No.
I'll be surprised unless George is late. No.

These should be phrased as their counterparts with 'if', thus:

Tom's mother will be worried if he isn't home by midnight. OK.
Martha will be sad if she doesn't get a letter from Fred. OK.
I'll be surprised if George is on time. OK.


These adjectives of emotional reaction sometimes occur with 'unless' when they occur with a negative polarity item, however.

The broker won't be happy unless the fund makes a lot of money. OK.

And they sometimes occur with 'unless' when an affirmative is a general claim:

Film-goers will be completely surprised unless they have already read the book. OK.

CJ

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Comments  

These adjectives of emotional reaction sometimes occur with 'unless' when they occur with a negative polarity item, however.

The broker won't be happy unless the fund makes a lot of money. OK.

And they sometimes occur with 'unless' when an affirmative is a general claim:

Film-goers will be completely surprised unless they have already read the book. OK.

CJ

Please what do you mean when you wrote that unless occurs with negative polarity item?

Also in this sentence ,isn't there an emotional state here? And you said that will be + emotional state can't be used with unless.

Film-goers will be completely surprised unless they have already read the book. OK.

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مسك الياسمين

Please what do you mean when you wrote that unless occurs with negative polarity item?

Also in this sentence ,isn't there an emotional state here? And you said that will be + emotional state can't be used with unless.

Film-goers will be completely surprised unless they have already read the book. OK.

Negative polarity items:

not (n't), never, no, none, etc.

The last two examples show you cases where the general rule (given at the beginning of my post) does not apply.

CJ