Probability vs. obligation (deber de / deber)

Expressing obligation with "deber"

When talking about duties, rules, or things that simply must be done—like the careful work of a beekeeper—use the verb deber followed by an infinitive. In this context, it translates to "must" or "ought to" do something.

The beekeeper must wear the veil to avoid stings.
El apicultor debe usar el velo para evitar las picaduras.
The beekeepers must inspect the hive today.
Los apicultores deben revisar la colmena hoy.
We must extract the honeycomb very slowly.
Debemos extraer el panal muy despacio.

Expressing probability with "deber de"

In English, we also use "must" to make strong guesses or logical conclusions, like saying "That honey must be expensive." In Spanish, to express this kind of probability or supposition, you add the preposition de after the verb, forming the phrase deber de + infinitive.

Without the de, it sounds like an obligation or a command. With the de, it becomes a strong assumption.

That wild honey must be very expensive.
Esa miel silvestre debe de ser muy cara.
The swarm must be near the hive.
El enjambre debe de estar cerca de la colmena.
Extracting the honey must be difficult; however, I like it.
Extraer la miel debe de ser difícil; sin embargo, me gusta.