Learn Portuguese (Portugal): Alguém terá deixado a pegada na lama. - Someone must have left the footprint in the mud.

Alguém terá deixado a pegada na lama.

Someone must have left the footprint in the mud.

Breakdown of Alguém terá deixado a pegada na lama.

to leave (behind) / to quit / to let (allow)

Questions & Answers about Alguém terá deixado a pegada na lama.

Why does the Portuguese sentence use a future tense (terá deixado) to talk about a footprint that was already left in the past?

This is the exact focus of your current lesson! In Portuguese, the Futuro Composto (future perfect) is frequently used to express an assumption, probability, or deduction about something that happened in the past. Even though it literally translates to "will have left", in this context it means "must have left" or "probably left".

Could I use the verb dever to express this same "must have" idea?

Yes, absolutely. You could say Alguém deve ter deixado a pegada na lama, which means exactly the same thing. Using the Futuro Composto (terá deixado) is simply a more elegant, slightly more literary alternative to deve ter deixado, which is very common in everyday spoken Portuguese.

Do I need to include a word like provavelmente (probably) for the sentence to make sense as an assumption?

You don't need to! The compound future tense itself already builds the "probably" or "must have" meaning into the verb. Adding a word like provavelmente wouldn't be grammatically wrong, but it is entirely unnecessary because terá deixado carries that deductive meaning all on its own.

Since a pegada (the footprint) is a feminine noun, shouldn't the past participle agree with it and become deixada?