The Grammaring Guide to English Grammar with Exercises

Third conditional

IF + PAST PERFECT SUBJUNCTIVE | WOULD + PERFECT INFINITIVE

The third conditional describes an unreal situation with reference to the past. We imagine a hypothetical situation, something that did not happen:

If the driver

had fastened

his seat belt, he

would

probably

have survived

the accident.

Here If the driver had fastened his seat belt means that he did not fasten his seat belt.

In the if-clause, we use the past perfect subjunctive form of the verb, which is identical to the past perfect tense:

If we

had booked

our flight earlier, it would have been cheaper.

If you

had taken

a taxi, you would have caught the train.

If I

had revised

more, I would have done better on my exam.

Quotes:

If the Romans had been obliged to learn Latin, they would never have found time to conquer the world. - Heinrich Heine

Related topics:

Past perfect subjunctive

The modal WOULD to express unreal situations

Wishes about the past

AS IF / AS THOUGH

WOULD RATHER / WOULD SOONER + perfect infinitive

WOULD RATHER / WOULD SOONER + clause with the past perfect subjunctive

Past perfect continuous subjunctive in the third conditional

The past perfect continuous subjunctive can be used in the if-clause of a sentence in the third conditional to express an unreal action in the past which is imagined as continuous:

If the driver

had been wearing

a seat belt, he would probably have survived the accident.

If I

had been living

in New York at the time, I would have gone to the show.

If I

hadn't been working

all day, I would have gone jogging.

Modals in the third conditional

Main clause

We can use modals other than would in the main clause of a sentence in the third conditional:

If I had had the right tools, I

could have fixed

my bike.

(ability)

If the weather had been worse, they

might not have reached

the top.

(possibility)

If-clause

We can use could + perfect infinitive in the if-clause to express ability or possibility:

If he

could have got

to the station on time, he might have caught the train.

(ability)

If I

could have known

this would happen, I'd never have started dating him.

(possibility)

Were to + perfect infinitive is also possible in the if-clause; however, it is less common:

If he

were to have asked

me, I would have said yes.

Related topics:

Modals to express ability: CAN, COULD, BE ABLE TO

Modals to express possibility: MAY, MIGHT, CAN, COULD