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
Unreal conditionals can be used to give advice if they begin with "If I had been you". The if clause is often omitted. Unreal conditionals sound more polite and are more indirect than advice phrased with should have.
Advice with Past Unreal Conditionals
(If I'd been you,) I would not have bought the dress.
Advice with Modals
You shouldn't have bought the dress.
Restating Past Unreal Conditionals with But
Often, a sentence with would have is used without an if condition. Instead, the main clause is joined to a true (not imaginary) sentence with but. As you can see in the sentences below comparing the unreal conditional and the sentences with but, they mean the same thing.
True Sentence with But
I would have come to the movie, but I had to work.
I would have called you, but my cell phone didn't work.
Past Unreal Conditional
I would have come to the movie if I hadn't had to work.
I would have called you if my cell phone had worked.
Exercise
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