Third Conditional — Exercises on If I Had Known
Practice the third conditional: if I had known, I would have come; could have, might have — imagining a different past that can no longer change.
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We left home late yesterday. If we ___ earlier, we would have caught the train.
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had left
Yesterday is finished and we can't change it → third conditional: 'if' + past perfect ('had left'). 'Would have' belongs only in the other half of the sentence.
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I didn't know it was your birthday. If I'd known, I ___ you a present.
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would have bought
The birthday is in the past and I didn't buy anything → third conditional result: 'would have' + past participle ('would have bought').
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Luckily you reminded me. If you hadn't, I ___ to call my mum on her birthday.
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would have forgotten
You did remind me, so I called her — the result is an imagined past → 'would have forgotten'. 'Had forgotten' is the form for the 'if' part, not the result.
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We ___ lost on that walk last Sunday if we had taken a map with us.
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wouldn't have got
Last Sunday is finished: we didn't take a map and we got lost → third conditional result: 'wouldn't have' + past participle ('wouldn't have got').
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We ___ the match last Saturday if our best player hadn't been injured.
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would have won
The match was last Saturday and we lost → result in the past: 'would have won'. 'Would win' would be about now or the future.
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I'm so sorry — if I'd known you were vegetarian, I ___ chicken last night.
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wouldn't have cooked
The dinner was last night and I did cook chicken → unreal past result: 'wouldn't have cooked'. 'Hadn't cooked' is an 'if'-part form, and 'wouldn't cook' would be about now.
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If you'd told me the meeting was cancelled, I ___ all the way into the office this morning.
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wouldn't have driven
I drove in this morning and the trip is over — an unreal past result → 'wouldn't have driven'. 'Hadn't driven' is an 'if'-part form.
Third Conditional: Imagining a Different Past
The third conditional is if + past perfect with would have + past participle: If we had left earlier, we would have caught the train, If I'd known it was your birthday, I'd have bought you a present. Both halves describe the past, and both are the opposite of what really happened: we left late, and we missed the train. Because the event is finished, the third conditional is often used for regret, criticism or relief: If you hadn't reminded me, I would have forgotten. Could have and might have replace would have for ability or possibility. In speech, 'd stands for had in the if clause and for would in the result: If I'd known, I'd have come. The two common errors are would have in the if clause (If I would have known) and a missing have in the result (I would come to your party last week).
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