If + Present tense, … will/won’t …
– We use the first conditional to talk about things that we think might happen in the future.
– E.g.: If I find your watch, I will tell you.
(You’ve lost your watch, and I’ll look for it – perhaps I’ll find it)
If + Past tense, … would/wouldn’t …
– We use the second conditional to imagine unreal things in the present:
a) We use it to imagine things that we don’t expect to happen
e.g.: If I found a watch in the street, I‘d (= I would) take it to the police.
(No-one has really lost a watch – I’m just imagining the situation)
b) We use it to imagine things that can’t be true
e.g.: If I lived in Hawaii, I‘d go swimming every morning.
(I don’t live in Hawaii – I’m just imagining it)
– In second conditionals, we can use were instead of was. This is used in a more formal style, and also in the phrase If I were you:
e.g.: If I were you, I’d see a doctor.
If + past perfect tense, … would/wouldn’t have (done)
– We use the third conditional to imagine unreal things in the past
– E.g.: If I’d known (=had known) you were alone, I would have visited you.
(Unfortunately I didn’t know, so I didn’t visit you.)
– E.g.: I would have been upset if they hadn’t invited me to the party.
(In fact they did invite me, so it was all right.)
– We can mix second and third conditionals in one sentence. One part can refer to the present (second conditional) and one part can refer to the past (third conditional)
– E.g.: If I’d (= I had) remembered to buy some petrol, we’d (= we would) be home by now.
(You didn’t remember, so we are not home now.)