Adverb clause of condition
The adverb clause of condition gives the circumstances under which the action in the main clause will take place.
Common subordinating conjunctions used to introduce adverb clauses of condition are: if, unless, whether, provided that, on condition that and so long as.
If it rains, we will not go out.
She will come if you invite her.
You won’t pass unless you work hard.
That’s Mathews, unless I am mistaken.
Note that unless means if not. Therefore, it would be wrong to use another not in clauses with unless.
Unless you give me the keys, you will be shot. OR If you do not give me the keys, you will be shot. (NOT Unless you do not give me the keys, you will be shot.)
We will have plenty to eat provided that no more than twenty people turn up.
You can take my car so long as you drive carefully.
There will be no trouble as long as you keep your mouth shut.
She will take this medicine whether she likes it or not.
I will forgive you on condition that you don’t do that again.
Difference between whether and if
We do not usually use if in a two-part question with or; however, it is possible.
Let me know whether you can come or not. OR Let me know if you can come or not.