5

My wife will be angry, unless I'm home by 7.00.

In the sentence above the "unless" should not be used. The correct conjunction is supposed to be the "if". Compare this sentence:

I'll come at 5 unless there is a traffic jam.

Here "unless" is appropriate. Why is it not so in my example sentence?

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    Why do you believe you shouldn't use 'unless' in that sentence? It looks perfectly OK to me. Using 'if' would give it a different meaning, unless you add the word 'not'. "My wife will be angry, if I'm not home by 7.00." – ssav Sep 3 '15 at 11:39
  • In Practical English Usage by M. Swan this is the example of a mistake that make even very advanced students. Unfortunatelly, I do not have at disposal the full text of Swan so I do not know the explanation. – bart-leby Sep 3 '15 at 11:46
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    I used to use PEU often enough that I have reasons to believe that his book has a couple of flaws, and this is one of them. (This point, iirc, has been mentioned once or twice on ELL, if someone will try until they find it, it will be great.) It's not that his grammar point is invalid, but it's an unfortunate example. Another example is clearer: *I'll be surprised unless the car breaks down soon., which doesn't work with unless, but with if ... not, it works. In the wife example, I believe that Swan's wife is quite ideal. She's never been angry unless the husband is late. – Damkerng T. Sep 3 '15 at 13:38
  • But these days, I think it's not difficult to imagine a wife who is always angry at her husband, and the only way to better her mood is that the husband must arrive home in or on time. – Damkerng T. Sep 3 '15 at 13:42
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    I think the original sentence would look a bit better the other way around. "Unless I'm home by 7.00, my wife will be angry." I couldn't say why though. – ssav Sep 3 '15 at 15:51
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The reason that one of these examples is better than the other is not about grammar, it is about implications.

An implication is an idea that you might give to somebody, but that you didn't actually properly say. For example, if you say Give me my book back or I'll punch you, you are saying that you will punch the person if they do not give you back your book. But you are only implying that you will not punch the person if they do give your book back. But notice that you did not actually say this at all. Maybe you will punch them if they don't give it back and you will punch them if they do!

When we use the word if we often give people the idea that the situation in the main clause will be caused by the situation in the if-phrase:

  • It will break if you sit on it.

When we hear the sentence above, we understand something like:

  • If you sit on, it it will break because you sit on it.

Notice that that is just an implication. We did not actually say that!

When we use the word unless, we often give a different implication. Consider this sentence:

  • I play outdoor badminton on Tuesdays, unless it's cold outside.

In the sentence above, I am implying that the normal situation is that I play badminton on Tuesdays. I am implying that the situation you should expect is that I play badminton on Tuesdays. And I am also implying that somehow "it's cold outside" is an exception. It isn't what you would expect to happen. For this reason it would be very strange for me to say I play badminton on Tuesdays unless it's cold outside if I lived in the Arctic!

Getting it wrong

Implications are not usually accidents. People use implications to give people extra information without needing to use more words. If we want to show that some situation will cause another situation, it is better to use if than unless. Remember that chair sentence? Well if we use unless the sentence will sound very strange:

  • That chair will break unless you don't sit on it.

Now, if we are saying this to someone who is thinking about sitting down on a chair, this is a bit odd. This doesn't give the same implications as the if-sentence at all. It presents the chair breaking as something we might expect to happen, and it makes our not sitting on it sound like an unusual exception. The other reason it is odd is because if we wanted to imply that sitting on the chair would break it, we could just use the word if instead! It would be clear and effective. There is nothing wrong with the grammar in the unless-sentence. It just presents the information in a strange way, and doesn't use the implications of if or unless effectively.

It's important to remember that if and unless do not give opposite implications. They just give different ones. There are many situations where we could use either word and the implications would be useful.

Another thing to remember is that implications are very context-dependent. When the situation we use them in changes, the implications often change too. Also, the way that we arrange information in a sentence can give also different implications. This can change the types of implication that individual words would otherwise have.

The Original Posters examples

  1. I'll come at 5 unless there is a traffic jam.

  2. My wife will be angry, unless I'm home by 7.00.

The first example gives the implication that the listener should interpret the traffic jam as an exception to what is expected. The second example is not ungrammatical or untruthful. But if the speaker wants to say that not getting home by 7.00 will cause his wife to be angry it might be more effective to say:

  • If I get home after 7.00, my wife will be angry.

This is not the best example that Michael Swan could have given. But this is what he means.

  • I wonder if the "correct" answer is actually to use 'if...not' instead of just if. My wife will be angry if I'm not home by 7. (correct) My wife will be angry unless I'm home by 7. (not correct) My wife won't be angry, unless I'm late. (correct). I know that colloquially, it is OK to say "Dad will get angry unless I get home by my curfew." but it really isn't 100% correct. – ColleenV May 5 '16 at 16:41
  • @ColleenV Yes, that would certainly work too, and might be best. I don't think the others are wrong, but they're weird! – Araucaria May 5 '16 at 16:47
  • I meant that the comment in the question 'The correct conjunction is supposed to be the "if"' (according to PEU) may be a little misleading because the 'not' is missing - I don't have access to the full text, so I can't say what Swan meant exactly. It isn't a great example sentence regardless. – ColleenV May 5 '16 at 16:52
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My wife will be angry unless I'm home by 7

If I'm not home by 7, my wife will be angry

In some ways, these two sentences are equivalent. They mean that if you get home at 7:05, your wife will be angry.

However, there's a difference in the detail.

If I'm not home by 7, my wife will be angry

This assumes that your wife is not angry, and will only become angry if you are late.

My wife will be angry unless I'm home by 7

This assumes that your wife will be angry, and the only way to placate her is to arrive home early.

It's a fairly subtle distinction, and frankly I think your book is being over-zealous as any native speaker would understand the intended meaning without issue.


To transfer this to your other sentence

I'll be home by 5pm, unless there is a traffic jam

As above, the assumption is that you will be home at 5pm.

Again, "unless" gives the assumption that the former clause is always true with the exception of the situation in the second clause.

I will be home late if there is a traffic jam

Now the assumption is that the first phrase is only true if the second is also true.

In this example, both are relevant because the initial position is that you are home on time, not that your wife is angry.

The "wrong" version of this sentence would be something more like the following, which perhaps shows why it is wrong.

I will be home late unless I get home on time.

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