Certainty
How sure is the speaker that this is true?
Significado
Certainty shows how sure the speaker is that a statement is true. The speaker can present something as certain, likely, or doubtful. Languages use words, verb forms, or tone of voice for this, and some have no special certainty form. How the speaker knows concerns the source of the information, not how strongly the speaker believes it.
Como identificar
Look for what makes a statement sound certain, likely, or doubtful, rather than simply describing what happens.
Na tua língua materna
Certainty is usually shown with words and phrases such as com certeza, provavelmente, and não tenho certeza. Dever plus an infinitive, the verb form used to name an action or state, can express a likely conclusion rather than a duty, so the surrounding message matters.
Com certeza, a Ana vai gostar deste lugar.
O Paulo provavelmente ainda está no trabalho.
Ela deve estar no ônibus; o celular está desligado.
Deve expresses a guess, not a requirement.
Na tua língua de aprendizagem
English uses words such as definitely, probably, and maybe to show different levels of confidence. Must can express a strong conclusion, while may, might, and could express uncertainty about what is true. In this use, must does not give an order and may does not give permission.
The lights are on. Anna must be home.
Must expresses a strong conclusion, not a duty.
Ben might be on the bus.
The speaker presents this as possible, not certain.
They'll probably arrive before lunch.
Probably presents the arrival time as likely, but not certain.
Learners whose language separates words for rules from words for guesses may mistake must for an obligation or may for permission in these uses.