* You can use a modal in a conditional clause.
* You use `unless’ to mention an exception to what you are saying.
1 You sometimes use modals in conditional clauses. In the main clause, you can still use a present tense for events that happen often, `will’ for events that are quite likely in the future, `would’ for an event that is unlikely to happen, and `would have’ for events that were possible but did not happen.
If he can’t come, he usually phones me.
If they must have it today, they will have to come back at five o’clock.
If I could only find the time, I’d do it gladly.
If you could have seen him, you would have laughed too.
`Should’ is sometimes used in conditional clauses to express greater uncertainty.
If any visitors should come, I’ll say you aren’t here.
2 You can use other modals besides `will’, `would’ and `would have’ in the main clause with their usual meanings.
She might phone me, if she has time.
You could come, if you wanted to.
If he sees you leaving, he may cry.
Note that you can have modals in both clauses: the main clause and the conditional clause.
If he can’t come, he will phone.
See Units 79 to 91 for more information.
3 In formal English, if the first verb in a conditional clause is `had’, `should’, or `were’, you can put the verb at the beginning of the clause and omit `if’.
For example, instead of saying `If he should come, I will tell him you are sick’, it is possible to say `Should he come, I will tell him you are sick’.
Should ministers decide to hold an inquiry, we would welcome it.
Were it all true, it would still not excuse their actions.
Had I known, I would not have done it.
4 When you want to mention an exception to what you are saying, you use a conditional clause beginning with `unless’.
You will fail your exams.
You will fail your exams unless you work harder.
Note that you can often use `if…not’ instead of `unless’.
You will fail your exams if you do not work harder.
When you use `unless’, you use the same tenses that you use with `if’.
She spends Sundays in the garden unless the weather is awful.
We usually walk, unless we’re going shopping.
He will not let you go unless he is forced to do so.
You wouldn’t believe it, unless you saw it.
5 `If’ and `unless’ are not the only ways of beginning conditional clauses. You can also use `as long as’, `only if’, `provided’, `provided that’, `providing’, `providing that’, or `so long as’. These expressions are all used to indicate that one thing only happens or is true if another thing happens or is true.
We were all right as long as we kept our heads down.
I will come only if nothing is said to the press.
She was prepared to come, provided that she could bring her daughter.
Providing they remained at a safe distance, we would be all right.
Detergent cannot harm a fabric, so long as it has been properly dissolved.