0) ZERO/PRESENT CONDITIONAL
if + present simple, present simple/imperative
- used to refer to conditions which are always true, are scientific facts; or to give instructions
- in zero conditional when or whenever can be used instead of if
Ex.: Mike feels sick if he reads on the train.
If you put paper on the fire, it burns quickly.
If the phone rings, answer it.
1) FIRST CONDITIONAL
if + present simple, will + infinitive
- used to predict likely or probable results in the future, to express promises, warnings and threats
- based on facts in real time
- may and must can be used instead of will
- should and happen to can be used in the condition clause to suggest that something is unlikely to happen
- when will appears in the condition clause, it expresses willingness, refusal or insistence (when it expresses insistence, it is stressed and never contracted) If you will wash the dishes, I'll put them away.
Ex.: We will/may miss the train if we don't leave now.
If you happen to see Peter, tell him I need to talk to him.
2) SECOND CONDITIONAL
if + past simple, would/could/ might + infinitive
- used for imaginary or improbable situations, to express advice or refer to unreal situations
- were is often used instead of was, especially in formal style
- used to make suggestions sound more polite
Ex.: You'd have to have several injections if you went to Africa.
If you worked harder, you might pass the exam.
I wouldn't drive so fast if I were you.
3) THIRD CONDITIONAL
if + past perfect, would/might/could + have + past participle
- used to speculate about possibilities in the past that did not happen
Ex.: If I had known it, I wouldn't have gone there.
I'd have sent you a postcard if I had known your address.
You might have not crashed into the bus if you'd been driving more slowly.