Spanish modal verb Deber versus Deber de (obligation and assumption)

Different uses of deber in Spanish

The verb deber (must) in Spanish has a specific use and meaning when it is followed by preposition "de". We use it to express a strong assumption about the action in the main verb used in the sentence.

Have a look and listen to the following examples:

As a general rule, deber directly followed by an infinitive (without de) means obligation although its use to express assumption is also accepted:

Both sentences above are correct, expressing a strong assumption.

Let's see another example:

You can see above that deber + infinitive could mean both, but deber de + infinitive is only considered an assumption, not an obligation.

Bear in mind that deber (de) can also be used in other tenses:

For example:

And can also be followed by El Infinitivo Compuesto when we are talking about assumptions related to past actions.

For example:

To learn about other ways to express probability/assumption see: 

• Using the simple future in Spanish for prediction, speculation and probability in the present (El Futuro Simple)