BertCornillie. Evidentiality and epistemic modality in Spanish (semi-)auxiliaries. A cognitive-functional approach. BertCornillie. Berlin: Mouton De Gruyter, 2007. 313 p.
Aikhenvald, Alexandra Y.2004. Evidentiality. Oxford: Oxford University Press.
Silva-Corvalán, Carmen. 1995. “Contextual conditions for the interpretation of ‘poder’ and ‘deber’ in Spanish”. Modality in grammar and discourse ed. por Joan Bybee y Suzanne Fleischmann. 67–105. Amsterdam: John Benjamins.