This article discusses the diachronic development and the different uses of the reportative word dizque (diachronically based on diz que ‘she/he/it says that’) using data from Colombian and Mexican Spanish. The study presents a predominantly qualitative analysis of diachronic, twentieth- and twenty-first-century written data. The theoretical framework applied in this article is Functional Discourse Grammar (FDG), which is particularly useful in this context as it distinguishes between the interpersonal and representational functions of language. The main points made are: (i) dizque is an adverb that arose from a process of lexicalization rather than grammaticalization; (ii) in most of its uses, dizque has an interpersonal function in the sense that the Speaker instructs the Addressee that she/he is not the source of the information provided; (iii) by means of diachronic, dialectal, and typological data, it is shown that the scope of dizque is gradually decreasing; (iv) the only scope decrease that leads to a functional change of dizque is its application outside the context of speech-reports. FDG serves to account for each step in the scope decrease of dizque by means of its hierarchical approach to the actional and descriptive functions of verbal interaction.