Third conditional

The third conditional: if + had + past participle (past perfect), would have + past participle. We use it to imagine the past turning out differently — both the condition and the result are unreal, because it has already happened.

Short forms: If I'd known (had), I'd have come (would), I would've come. In fast speech, would have sounds almost like “would-ə”.

💡'd in the if-clause is had (If I'd known); in the result it is would (I'd have gone). And because would've sounds like “would of”, people often misspell it — always write would have.

1. Imagining a different past — what really happened was the opposite

• If I had left earlier, I wouldn't have missed the train.

  I left late and missed it

• If Lan hadn't helped me, I would have failed the course.

  but Lan did help me

2. Regret or blame about something in the past

• If you'd told me it was your birthday, I'd have bought you a cake.

• We would have won if we hadn't made so many mistakes.

3. Relief that something bad didn't happen

• If the neighbours hadn't smelled the smoke, the whole house would have burned down.

• If you hadn't reminded me, I would have forgotten my passport.

In the result you can use could have + V3 (= would have been able to) or might have + V3 (= would perhaps have) instead of would.

• If we'd booked earlier, we could have sat together.

  could have = would have been able to

• If she had applied, she might have won the scholarship.

  might have = would perhaps have

Work out the time of each clause. A clause about the past → had V3 / would have V3; a clause about now → past simple / would + verb. When the two clauses are about different times, you get a mixed conditional.

• If I had studied medicine, I would be a doctor now.

  past → present

• If we hadn't moved to Da Nang, we wouldn't know each other.

  past → present

• If he were more organised, he wouldn't have forgotten the meeting.

  present → past

• If I didn't have to work tomorrow, I would have stayed at the party longer.

  present → past

💡Mixed 1 often has now, today, still in the result. If you see “now” and the if-clause has had V3, the result takes would + verb, not would have.

In formal English you can drop if and put had before the subject: Had I known = If I had known. The negative is Had … not + V3 (not shortened to Hadn't I…). See the lesson “Inversion”.

• Had we known the road was closed, we would have gone another way.

• Had she not called, I would have waited all night.

  not: Hadn't she called

• ✗If I would have known, I would have come.

  ✓If I had known, I would have come.

  The if-clause takes had + V3. “If I would have…” is heard in casual speech but is not standard.

• ✗If I knew you were in hospital, I would have visited you.

  ✓If I had known you were in hospital, I would have visited you.

  It's about the past → had known.

• ✗We were late. If we had taken a taxi, we would arrive on time.

  ✓We were late. If we had taken a taxi, we would have arrived on time.

  The result is also in the past → would have + V3.

• ✗If she had took the medicine, she would have felt better.

  ✓If she had taken the medicine, she would have felt better.

  had + past participle (taken), not the past simple.

• ✗If she had asked me, I would of helped her.

  ✓If she had asked me, I would have helped her.

  would've sounds like “would of”, but it is always have.

• ✗If it had not rained, we would have play tennis.

  ✓If it had not rained, we would have played tennis.

  would have + past participle.