(Simple and Progressive)
The English perfect conditional expresses something that would have happened. It's commonly used in the main clause of a would have-condition (aka 3rd conditional or Type III conditional), which refers to an an impossible condition in the past and its hypothetical result. The simple perfect conditional is conjugated as would have + past participle.
- If you had worked harder, you would have passed the exam.
- She would have baked cupcakes if she had had known you were coming.
The progressive perfect conditional indicates a hypothetical result as an unfinished or continuous action and is conjugated as would have been + past participle.
- I would have been sitting in the garden if the sun had been shining.
- If Johnny had known it was dangerous, he wouldn't have been climbing the tree.