Third conditional

Form

if + subject + past perfect tense, subject + modal + have + past participle
If- (or dependent) clause, main clause
(Condition clause, result clause)

subject + modal + have + past participle + if + subject + past perfect,
main clause + if- (or dependent) clause
(Result clause + condition clause)

Use the third conditional for unreal events in the past

Discussing causes of past events or expressing feelings about them

We use the third conditional to talk about past events that did not happen as an alternative to what did happen. This is common when discussing the causes of events, especially when expressing regret or criticism when something bad happens or relief after we avoid something bad.

If we'd booked in advance, we would have got a table.
Reality: We didn't book in advance, so we didn't get a table.
Context: Explaining the failure to get a table.

If you hadn't been so careless, you wouldn't have lost your wallet.
Reality: You were careless, so you lost your wallet.
Context: Criticising the listener for losing his wallet.

If a passer-by hadn't called an ambulance, I would have died.
Reality: A passer-by called an ambulance and I didn't die.
Context: Expressing relief at being saved.

If we'd done more advertising, more people would have come.
Reality: We didn't do much advertising, so not many people came.
Context: Discussing the disappointing turnout for an event.

If we'd delayed the launch, I don't think it would have been so successful.
Reality: We didn't delay the launch and it was successful.
Context: Analysing reasons for the success of a product etc.

Mixed conditionals

Some conditional sentences do not follow the time relationships shown above. See mixed conditionals for more details.

Use could, may, might and other modals in the result clause when appropriate

It is common to use other modals besides would in the result clause to express various ideas. These all use the same modal perfect form: modal + have + past participle

Less certain results

If you'd fallen, you would have been killed.
Certain result.
If you'd fallen, you may / might / could have been killed
Uncertain result.

Possibility

If I'd studied harder at school, I could have gone to university.
Possible result - It would have been possible to go to university.

Third conditional sentences can be made without if

Various alternative structures and phrases can be used to make third conditionals.

Had [I] (not)...

This is used in a more formal style.

Had she known about the problems, she wouldn't have bought it.
If she had known about the problems, she wouldn't have bought it.

Had I not taken out insurance, it would have cost me a fortune.
If I hadn't taken out insurance, it would have cost me a fortune.

But for... / If it hadn't been for...

These forms are used to emphasize that someone or something was responsible for a particular outcome (good or bad)

But for Cynthia, we would all have got lost.
If it hadn't been for Cynthia, we would all have got lost.
Cynthia saved us from getting lost.

But for the time we wasted looking for a petrol station, we would have got there on time.
If it hadn't been for the time we wasted looking for a petrol station, we would have got there on time.
If we hadn't wasted time looking for a petrol station, we would have got there on time.

A noun or noun phrases follows for in both structures.

ESL quizzes for third conditional

quiz

Wishes - regrets - conditionals analysis quiz

Wishes - regrets - conditionals - completion quiz

Past conditionals, wishes and regrets quiz