Page 211 - Advanced English Grammar in Use

I f . . . n o t a n d u n l e s s ; i f a n d w h e t h e r , e t c .

A if ...not and unless
Unless is used in conditional sentences with the meaning 'if...not':
• There's no chance of you getting the job unless you apply, (or ...if you don't apply.)
• You can't travel on this train unless you have a reservation, (or ...if you don't have...)
With unless we use present tenses when we talk about the future:
• Unless it rains, I'll pick you up at 6.00. (not Unless it will rain...)
In most real conditional sentences (see Unit 99), we can use either unless or if...not with a
B
similar meaning. However, we use if...not but not unless:
• in most unreal conditional sentences:
• He would be happier if he didn't take things so seriously, (not ...unless he took...)
• If she hadn't gone to university, she would have gone into the police force, (not Unless she
had gone...)
• when we talk about emotions:
• I'll be amazed if Christie doesn't win. (not ...unless Christie wins.)
• in most questions:
• If you don't pass the test, what will you do? (not Unless you pass...)
We use unless but not if...not when we introduce an afterthought.
• Without Philip to run it, the course can't continue - unless you want the job, of course, (not
... - if you don't want...)
In written English, the afterthought is often separated from the rest of the sentence by a dash.
if and whether
We can use if or whether to say that two possibilities have been talked about, or to say that
people are not sure about something:
• They couldn't decide whether/if it was worth re-sitting the exam.
• I doubt whether/if anyone else agrees with me.
Whether can usually be followed directly by or not. Compare:
• I didn't know if Tom was coming or not. (not ...if or not Tom was coming.) and
• I didn't know whether or not Tom was coming, (or ...whether Tom was coming or not.)

We prefer whether rather than if:
• after the verbs advise, consider, discuss:
• You should consider carefully whether the car you are interested in is good value.
• before to-infinitives and after prepositions:
• I couldn't decide whether to buy apples or bananas.
• We argued about whether women are more liberated in Britain or the USA.
• in a clause acting as a subject or complement:
• Whether the minister will quit over the issue remains to be seen.
• The first issue is whether he knew he was committing a crime.
• in the pattern noun + as to + whether to mean 'about' or 'concerning':
• There was some disagreement as to whether he was eligible to play for France.
Other nouns commonly used in this pattern are debate, discussion, doubt, question, uncertainty.

These sentences include other words and phrases used to introduce conditional clauses:
6) • We'll have the meeting this afternoon, provided/providing (that) no-one objects.
• Supposing (that) they ask me why I resigned from my last job - what should I say?
• I'll write to you every week - as/so long as you promise to reply.
Whether =» IfflTTl Conditionals (1) and (2) =