A guess about an earlier past
You already guess about the past with the future perfect: Se habrá ido = he has probably left. When you are back in a past moment and guess about something even earlier, the verb moves back one step, to the conditional perfect: habría + participle.
| guessing from now | guessing from a past moment |
|---|
| No contesta: habrán salido. | No contestó: habrían salido. |
The call is past, and the leaving came before it.
As a question, it is the worry you had at the time:
In reported speech
When you report words that were in the future perfect with a past verb (dijo, prometió), they move back to the conditional perfect, just as terminaré becomes terminaría.
| what was said | reported later |
|---|
| «Para el lunes habré terminado.» | Dijo que para el lunes habría terminado. |
Both promises were about a moment that was still ahead when they were made.
Hubiera for habría
For what would have happened, or what you would have liked, Spanish can also use hubiera + participle. Me habría gustado and Me hubiera gustado mean the same, and in Spain you will hear hubiera very often in conversation. Only in this sense, though: for a guess (habrían salido) or in reported speech (dijo que habría terminado), hubiera is not possible.
This is a common way to ask for someone's opinion about a past decision.
