Main points

* You use conditional clauses to talk about a possible situation and its results.

* Conditional clauses can begin with `if’.

* A conditional clause needs a main clause to make a complete sentence. The conditional clause can come before or after the main clause.

1 You use conditional clauses to talk about a situation that might possibly happen and to say what its results might be.

You use `if’ to mention events and situations that happen often, that may happen in the future, that could have happened in the past but did not happen, or that are unlikely to happen at all.
If the light comes on, the battery is OK.
I’ll call you if I need you.
If I had known, I’d have told you.
If she asked me, I’d help her.

2 When you are talking about something that is generally true or happens often, you use a present or present perfect tense in the main clause and the conditional clause.
If they lose weight during an illness, they soon regain it afterwards.
If an advertisement does not tell the truth, the advertiser is committing an offence.
If the baby is crying, it is probably hungry.
If they have lost any money, they report it to me.

WARNING: You do not use the present continuous in both clauses. You do not say `If they are losing money, they are getting angry.’

3 When you use a conditional clause with a present or present perfect tense, you often use an imperative in the main clause.
Wake me up if you’re worried.
If he has finished, ask him to leave quietly.
If you are very early, don’t expect them to be ready.

4 When you are talking about something which may possibly happen in the future, you use a present or present perfect tense in the conditional clause, and the simple future in the main clause.
If I marry Celia, we will need the money.
If you are going to America, you will need a visa.
If he has done the windows, he will want his money.

WARNING: You do not normally use `will’ in conditional clauses. You do not say `If I will see you tomorrow, I will give you the book’.

5 When you are talking about something that you think is unlikely to happen, you use the past simple or past continuous in the conditional clause and `would’ in the main clause.
If I had enough money, I would buy the car.
If he was coming , he would ring.

WARNING: You do not normally use `would’ in conditional clauses. You do not say `If I would do it, I would do it like this’.

6 `Were’ is sometimes used instead of `was’ in the conditional clause, especially after `I’.
If I were as big as you, I would kill you.
If I weren’t so busy, I would do it for you.

You often say `If I were you’ when you are giving someone advice.
If I were you, I would take the money.
I should keep out of Bernadette’s way if I were you.

7 When you are talking about something which could have happened in the past but which did not actually happen, you use the past perfect in the conditional clause. In the main clause, you use `would have’ and a past participle.
If he had realized that, he would have run away.
I wouldn’t have been so depressed if I had known how common this feeling is.

WARNING: You do not use `would have’ in the conditional clause. You do not say `If I would have seen him, I would have told him’.