Learn Portuguese (Portugal): De facto, o faroleiro deve de estar muito sozinho. - In fact, the lighthouse keeper must be very lonely.

Adding de after dever specifically marks probability or a strong assumption. While you will often hear Portuguese speakers just say deve estar for the same meaning, using deve de estar removes any possible confusion with obligation or duty. It purely expresses a logical deduction.

How is the word faroleiro formed?

It combines farol (lighthouse) with the suffix -eiro, which is incredibly common in Portuguese for professions or habitual roles. You see this same pattern in words like padeiro (baker) from pão (bread) or bombeiro (firefighter) from bomba (pump).

Why use estar rather than ser with sozinho?

We use estar because being alone or lonely here is a condition of his current situation at the lighthouse. If you used ser sozinho, it would describe a permanent, inherent trait, implying he is a loner by nature or has absolutely no family or friends in his life.

Is de facto always spelled with a 'c' in European Portuguese?

Yes, in European Portuguese, the 'c' in de facto is both written and clearly pronounced. It translates to 'in fact' or 'as a matter of fact' and is a great connector to confirm or emphasize a logical deduction, tying perfectly into the assumption we are making with deve de.