Logical assumptions (deber de)

Wrapping and Guessing

When handling gifts, you might need to wrap (envolver) them or untie (desatar) a knot.

I want to wrap the gift, but I do not have the wrapping.
Quiero envolver el regalo, pero no tengo el envoltorio.
She unties the knot to open the mysterious package.
Ella desata el nudo para abrir el paquete misterioso.

If you are curious, you might guess (adivinar) what is inside if the package is lightweight (ligero) or by giving it a shake (agitar).

The package is very lightweight, can you guess what it is?
El paquete es muy ligero, ¿puedes adivinar qué es?

Logical Assumptions: deber de

To make a logical deduction or express strong probability, use deber de + infinitive.

While deber + infinitive expresses obligation (what someone must do), deber de + infinitive expresses a logical assumption (what must be true). Conjugate deber to match the subject of your deduction.

The box is very lightweight and must be empty.
La caja es muy ligera y debe de estar vacía.
The box is moving, it must be an animal!
La caja se mueve, ¡debe de ser un animal!

You can use this structure to guess the reason behind an action or to estimate the time.

He dropped the package because it must weigh a lot.
Se le ha caído el paquete porque debe de pesar mucho.
It must already be three o'clock and they have not arrived yet.
Ya deben de ser las tres y todavía no han llegado.