The third conditional describes an unreal situation with reference to the past.
Imagine a Hypothetical situation, somthing that did not happen:
|If + Past Perfect Tense||would have + past participle|
If I had had enough money , I would have gone to Japan.
- Nature: unreal
- Time: Past (so we are talking about a situation that was not so in the past.)
e.g. If you had warned me, I would not have told your father about that party.(But you didn’t, and I have).