Like I think in English, (eu) acho que in Brazilian Portuguese can function as a discourse marker (DM) with more than one meaning, and these meanings are curiously diametrically opposed. Certainty, doubt or uncertainty is inferred by hearers in an interactional context. In a sample of audio-video recorded interviews, the occurrences of this DM were classified by meaning, and association tests between meanings and linguistic factors (pronoun realization, polarity, position in utterance), real-world features (type of evidence from which the speaker says something, and discursive topic), prosody (F0, intensity and duration), and facial expressions were carried out. Differences that distinguish these factors were identified among certainty, doubt and uncertainty uses. The certainty meaning of (eu) acho que was associated with pronoun presence, more formality and topics in which the speaker had direct evidence. Uncertainty and doubt were associated with pronoun absence, less formality and topics in which the speaker did not have direct evidence. Patterns of intensity and duration acted to distinguish the certainty, doubt and uncertainty meanings of (eu) acho que. In a conditional decision tree, the position in utterance, presence of a pronoun, type of speaker’s evidence, discursive topic, and duration helped to disambiguate the meanings of (eu) acho que. These results suggest the relevance of a multilevel approach to describe DM, in different languages, at least with respect to mental state verbs.
