Structure of third conditional

Structure of the 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 done it if you'd (you had) known earlier?
The third conditional - common mistakes
Common mistakes Correct version Why?
If I would have asked him, he would have helped me. 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.
If you had spoken to my mother, she would tell you where I was. 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.
test_inter4 Practise this grammar (intermediate level): Third conditional exercise
test_upper4 Practise this grammar (upper-intermediate level): Third conditional exercise