Past Unreal Conditionals
Past unreal conditional sentences are used to express imaginary situations that were not true in the past. The past perfect tense in the if clause shows that the situation was unreal in the past. In the main clause, would have, could have, or might have show that the result was also unreal in the past.
If I had been the employee, I would have defended myself. (I wasn't the employee, so I didn't defend myself.)
Both could have or might have in the main clause indicates one of several possible imaginary outcomes. On the other hand, would have is used to express a more certain imaginary outcome.
If you'd had left earlier, you would have caught the bus.
If you'd had left earlier, you might not have missed the bus.
If you'd had left earlier, you wouldn't have missed the bus.
Could have and might have both express one of several imaginary outcomes, while would have indicates a more certain imaginary outcome.
Giving Advice
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