Third conditional: when and how to use

How to form

Structure of third conditional
positive negative question
If I'd (I had) known you were coming, I would have waited for you. If she hadn't (had not) been ill, she would have gone to the cinema. Would you have told me if you'd (you had) known about it?

When to use

We use the third conditional to express a theoretical past situation and its theoretical result in the past:

[past theory] [theoretical result]
If I had studied more, . . . I would have passed the exam.
If I hadn’t come to America, . . . I wouldn’t have met you.
The third conditional – common mistakes
Common mistakes Correct version Why?
if I would have asked If I had asked him, he would have helped me. In the if-clause we use the past perfect (had + past participle). We don't use would or would have in the if-clause.
she would tell you If you had spoken to my mother, she would have told you where I was. The structure of the main clause is would + have + past participle.

Practise this grammar

upper-intermediate level: Third conditional exercise >>

intermediate level: Third conditional exercise >>