Introduction
Uncertain events and situations
In clauses after if, we usually talk about uncertain events and situations: things which may or may not happen, which may or may not be true, etc.
- Ask Jack if he’s staying tonight. (He may or may not be staying.)
- If I see Annie, I’ll give her your love. (I may or may not see Annie.)
Conditions
An if-clause often refers to a condition – something which must happen so that something else can happen.
- If you get here before eight, we can catch the early train.
- Oil floats if you pour it on water.
Clauses of this kind are often called ‘conditional’ clauses.
‘first’, ‘second’ and ‘third’ conditionals; other structures
Some students’ grammars concentrate on three common sentence structures with if, which are often called the ‘first’, ‘second’ and ‘third’ conditionals.
| ‘first conditional’ | |
|---|---|
| if + present | will + infinitive |
| If we play tennis, | I’ll win. |
| ‘second conditional’ | |
|---|---|
| if + past | would + infinitive |
| If we played tennis, | I would win. |
| ‘third conditional’ | |
|---|---|
| if + past perfect | would have + past participle |
| If we had played tennis, | I would have won. |
These are useful structures to practise. However, students sometimes think that these are the only possibilities, and become confused when they meet sentences like If she didn’t phone this morning, then she’s probably away (‘What’s this? A fourth conditional?’). It is important to realise that if is not only used in special structures with will and would; it can also be used, like other conjunctions, in ordinary structures with normal verb forms. (A research study carried out in the 1990s found that less than 25% of if-conditional sentences follow the traditional ‘first’, ‘second’ and ‘third’ patterns.)
Position of if-clause
An if-clause can come at the beginning or end of a sentence. When an if-clause comes first, it is often followed by a comma.
Compare:
- If you eat too much, you get fat.
- You get fat if you eat too much.
For other meanings of if, (see here).
For if and whether in indirect speech, (see here).
For if not and unless, (see here).
For more information about would/should, (see here), (see here), (see here).
For the difference between if and in case, (see here).
For even if, (see here).
How good are the rules?
The ‘rules’ given in this Section are intended to be useful for learners. They describe what happens most of the time, and are generally valid for formal speech and writing. However, usage is far from fixed, and educated speakers and writers quite often mix structures. So if a sentence is crossed out in one of the following explanations (e.g. If I would know her name, I would tell you) this means that it should be avoided in contexts like formal letters or examination scripts. It may not strictly speaking be wrong.
I’ll give her your love if I’ll see her. (see here)
If you asked me, I had told you. (see here)
If I would know his address I would tell you. (see here)
If I knew they had a problem, I could have helped them. (see here)
If I were to know his address, I would tell you. (see here)
Hadn’t we missed the plane, we would all have been killed in the crash. (see here)
It would of been better if we had started earlier. (see here)
If only I would know more people! (see here)
I only she didn’t tell the police, everything would have been all right. (see here)
I’ll be surprised unless the car breaks down soon. (see here)
I’ve bought a chicken in case your mother will stay to lunch. (see here)