SUJEITO NULO - NULL SUBJECT

Portuguese , as Spanish and Italian, allows sentences with null subjects. These are sentences where the subject ( for example , EU, VOCÊ, ELA, NÓS, ELES, A NAME, A NOUN) is not expressed. The listener/reader understands who or what the subject is because of the context and because of verb conjugation. For example, in the sentence EU SOU BRASILEIRA MAS MORO EM NOVA YORK, we find two verbs, SOU and MORO. The subject of SOU is EU; the subject of MORO is not expressed ( it is null ), but we know that the subject is also EU because of the context (the speaker is still talking about herself) and verb conjugation (first person singular ). Null subjects are also often found in answers for YES/NO questions: VOCÊ É BRASILEIRO? SOU, SIM.
ref.: Beginner's Brazilian Portuguese.