If + Past Perfect, would/wouldn’t + have+V3
Conditional 2 is used to talk about imaginary situations in the past (e.g. to express a lucky situation in the past or, on the contrary, to express regret).
E.g. If I hadn’t applied for this course, I wouldn’t have met you (but I applied for it – a lucky situation!).
If I had studied more, I would have passed the exam (but I didn’t study enough – regret).
Would you have believed me if I had told you the truth?
Note:
1.The contracted form for ‘had’ and ‘would’ is ‘d
If I’d (had) followed your advice, I’d (would) have accepted the invitation.
2.We can use could or might instead of would to express ability or probability respectively:
If they had trained more, they could have won.
If he hadn’t dropped out, he might have become a doctor.
3.We can use Past Perfect Continuous instead of Past Perfect to express a continuous action
If you had been looking where you were going, you wouldn’t have walked into the wall (criticism).