The English perfect conditional expresses something that would have happened. It's commonly used in the main clause of a would have-condition (also known as a 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.