Future perfect or conditional to talk about the past?

Question

Isn’t it ten simple conditional that is used to make supposition about the past?

Silvia Piriz · Accepted Answer

Hola Sally L.
Great question! Both the simple conditional and the future perfect can be used to make suppositions about the past, but they express slightly different things.
The simple conditional (e.g. estaría, tendría) is often used to make a general guess about the past, especially in indirect speech or reported thoughts.
For example:
Pensé que estaría en casa. (I thought he might be at home.)
The future perfect (e.g. habrá llegado) is used to make a supposition about something that you think has already happened, even if you're not sure:
Habrá llegado tarde. (He must have arrived late / He probably arrived late.)
So yes — you're right that the conditional can express a guess about the past, but the future perfect is also used that way, specifically when you’re speculating that something already happened.
Hope that helps clear it up!
Un saludo
Silvia