conditionnel zero

conditionnel zero

When we want to talk about things that are always or generally true, we can use

If/When/Unless plus a present form PLUS present simple or imperative.

If you press this button, you get black coffee.
When you fly budget airline, you don't expect to get anything to eat.
Unless you need a lot of leg-room, don't pay the extra for first class.
Notice that we are talking about something which is generally true, not a specific event.

In the condition clause, there can be a variety of present forms. In the result clause, there can only be the present simple or imperative.

If you visit Barcelona, look out for the spectacular architecture.
If unemployment is rising, people tend to stay in their present jobs.
If you've finished everything, go home.
When you go to Barbados, take plenty of sun cream.
When I'm working, please be quiet.
When I've written a new article, I run it through my spell-checker.
Notice that Unless means the same as if...not. Like if, it is followed by a present tense, a past tense or a past perfect (never by 'would'). It is used instead of if + not in conditional sentences of all types

Unless he asks you to continue, stop all work on the project.
Unless interest rates are rising, it's not a good investment.
You'll be sick unless you stop eating. (= You will be sick if you don't stop eating)
She would be here by now unless she was stuck in the traffic.
The elephant wouldn't have seen the mouse unless she'd had perfect eyesight

This is correct Soukayna! but one little thing : "Unless" means "if (and only if)" or "in the case when" not "if not".

"Unless he asks you to continue, stop all work on the project." => means that you'll have to stop all work on the project, but if (and only if) he asked you to continue, in this case, you have to continue.

thks for the information broth and i'll ask Mrs hilmi because i think that unless means if...not
for ex:You'll be unhappy unless you break up with her" = "You'll be unhappy if you don't break up with her."

Subconsciously, what you have just said is correct. However, the problem isn't about substitution, but the meaning slightly varies when add "if not" :
Let's review your last example :

- You'll be unhappy unless you break up with her.

If we replace "unless" with "if not" it would be :

- You'll be unhappy if you don't break up with her.

Both statements are grammatically acceptable, but there is a nuance :
The first statement suggests that breaking up with her is the only way to make you feel happy, the focus is on the act of breaking up (which is pitched) and the stress is more on the word "Unless". On the other hand, the second claims that not breaking up with her makes you unhappy. Here the focus is more on the result and the pitch is lower as the sentence advances. Moreover, the sentence also refers that there can be other events to cheer you up, not only breaking up with the girl! (in Arabic it is translated as "إلاّ إذا")

I hope I was clear enough.

unless=if not=الا ادا
what you have to understand is that the meaning of if not is الا ادا

I was interested in your discussion about the meaning of "unless" and its usage.You're both right ;
Unless = if … not. This is a good example of a 'rule of thumb' – one that is easy to remember and apply, but it's better to think of unless as meaning “except if…; except under these circumstances…”. So:

I’ll be at your place at 9.00, unless [= except if] the bus is late.
The front room was never used, unless [= except if] we had important visitors.

In the first sentence there is only one reason why I might be prevented from being at your place at 9.00, and that would be the bus being late. Likewise, in the second sentence there was only one circumstance when the front room was used: when we had important visitors.

But unless is unlikely here:

I’ll be angry if the bus isn’t on time.

In this sentence the bus not being on time is the reason for my being angry.The following sentence: "I’ll be angry unless [ = except if] the bus is on time."means: the only thing that will prevent me from being angry is the bus being on time – which sounds strange to say the least. Here are some more examples like that, where unless isn’t possible:
1. If you don’t like it, you can leave.
2. If she wasn’t so bossy, she’d be quite nice.
3. If I didn’t know a word, I’d look it up.

Here is an exercise that attempts to discriminate between these two meanings of if…not. Which of these sentences could you re-write with unless?

1. If you don’t have an umbrella, I’ll lend you mine.
2. If you don’t take an umbrella, you’ll get wet.
3. He’ll fail his exam if he doesn’t study.
4. I’ll be very disappointed if he doesn’t study.
5. Will it be all right if I don’t wear a tie?
6. They won’t let you in if you don’t wear a tie.
7. If it doesn’t rain in August the tourists will be happy.
8. If it doesn’t rain this August, there will be water shortages.
9. In the old days people never travelled if they didn’t really have to.
10. You’d sleep better if you didn’t drink coffee before bed.

Answers:

You can substitute if…not with unless in sentences 2, 3, 6, 8 and 9. Notice how unless seems often to occur in the context of bad or unfortunate things happening: is this perhaps a clue to how it's used – and a possible - more reliable – 'rule of thumb'?)