Unless and if ~ not

Question

Could you tell me what the difference of the meaning is between these sentences below?

1) I'll be surprised if Tom doesn't have an accident. He drives too fast.

2) I'll be surprised unless Tom has an accident. He drives too fast.

I understand "unless = if not", so 2) can be said like:

3) I'll be surprised if not Tom has an accident. He drives too fast.

I think 3) is equal with 1) in the meaning, right??

Thanks a lot!

Ozzourti · Accepted Answer

2 would roughly mean that the only way to prevent the speaker from being surprised is Tom having an accident.

3 would mean more or less that the speaker will be surprised if some other person than Tom has an accident.

Of course 1 seems to work best in your context.

H M · Answer

Thanks a lot for your explanation!
It helps me a lot!

Now I would like to know the differences between 1) if Tom doesn't do something and 2) if not Tom dose something...

I'm a bit confused...

Thank you so much in advance.

Ozzourti · Answer

"not" negates the noun/noun phrase that follows.

"not Tom" --> "someone else"

if Tom doesn't do that = if Tom himself does not do that
if not Tom does that = if someone else does that

I'll be surprised if not everyone passes the test. = I will be surprised if somebody fails it.

Clive · Answer

Now I would like to know the differences between
1) if Tom doesn't do something and 2) if not Tom does something...

#2 uses an incorrect word order.

Clive

H M · Answer

Dear ozzurti,

Thank you very much for your explanation again!
I think I got it! :-)

H M · Answer

Dear Clive,

Thank you for your correction!

BTW,

you say, #2 uses an incorrect word order.

Which means that this sentence ( 2) if not Tom does something... ) doesn't make sence??

Thank you in adcvance!

Ozzourti · Answer

H MWhich means that this sentence ( 2) if not Tom does something... ) doesn't make sence??

Well, that hardly makes any sense. I had to rack my brains to figure out what it could technically mean. Just use "if Tom doesn't do something" as I'm pretty sure that's what you want.

Clive · Answer

Which means that this sentence ( 2) if not Tom does something... ) doesn't make sence??
Yes, it doesn't make sense.

Clive

CalifJim · Answer

H MI understand "unless = if not"

Not always. In "surprised if" it works a little differently, and "unless" doesn't work.

You're talking about a case where Tom may or may not have an accident.
If he doesn't, you'll be surprised. If he does, you won't be surprised.

Here's the equivalent that I think you are looking for.

I won't be surprised if Tom has an accident.

This is logically equivalent to I won't be surprised unless Tom doesn't have an accident, but nobody would say it like that because it's too hard to follow all those negations.

Besides that, I don't see this as a normal conditional structure. It's more like a different way of saying the following, which contains no ifs:

Tom's not having an accident will surprise me(, and Tom's having an accident will not surprise me).

H M3) I'll be surprised if not Tom has an accident.

You can't use this one at all. The grammar is not correct.

CJ
____________________

Bonus information: Some speakers even make this construction with a pleonastic negative (unnecessary negation). They say:

I won't be surprised if he doesn't have an accident.

when they mean:

I won't be surprised if he has an accident.

CJ

H M · Answer

Thank you so much for your explanations!!!

It helps me a lot to understand better!!! :-)

Have a great day!

Unless and if ~ not

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