Third conditional [가정법 과거완료] 9A

Third conditional 
: If past perfect , Would have + past participle(과거분사)


1. 과거의 상황이 어떻게 달라졌을 지에 대해 말할 때 사용한다.
for hypothetical(가상의)/ imaginary situations.
Compare :
Yesterday I got up late and missed my train. (=the real situation)
If i hadn't got up late yesterday, I wouldn't have missed my train.
(= the hypothetical or imaginary past situation) 

2. If + past perfect(had + p.p), would(could, might) have + p.p

3. had 와 would는 'd 로 줄일수 있다. 
(the contraction(축소) of both had and would is 'd.)

4. 결과를 덜 확실하게 만들 때 would를 대신해서 might 또는 could를 사용한다. 
If she'd studied harder, she might have passed the exam. 

출처 : https://blog.naver.com/zak001/221297458825