Third and mixed conditionals

The third conditional imagines a different past: if plus the past perfect, then would have plus the participle: if I had left earlier, I would have caught the train.

A mixed conditional links a past condition to a present result: if I had studied medicine, I would be a doctor now. Or a present condition to a past result: if she were braver, she would have spoken.

In speech, would have sounds like would of, but it is always written have, or shortened to would've. Never write would had.