Third Conditional

The third conditional is used to express the past consequence of an unrealistic action or situation in the past.

The first action (studying hard) did not happen. But in the case that it happened, the consequence was passing the exam. 

The third conditional is very similar to the second conditional.

But while the second conditional refers to something unrealistic now or in the future, the third conditional refers to something unrealistic in the past.

If + past perfect, would/wouldn’t have + past participle.

Example: If you had told me about the meeting, I would have come.