If-Clauses in English Grammar: Third Conditional

The third conditional, also known as type III if-clause, refers to past situations and their outcomes and imagines them as different. It is also known as the impossible conditional because it talks about pasts situation that did not happen.

Construction

Rule 1: To form the third conditional, we use a past perfect for the if-clause, and would have + past participle for the main clause. If and would never appear in the same clause.

Note: We can reverse the order of the clauses with no change in meaning. But, if the if-clause comes first, it should be separated by a comma. If the main clause is first, we don't need a comma.

Rule 2: We can use the modal verbs could and might instead of would in the third conditional, but we do not use should.

Usage

Rule 3: We can use the third conditional to express regrets.

Rule 4: We can use the third conditional to give feedback and criticize.

Rule 5: We can use the third conditional to reflect on the past.