This paper explores the discourse functions of certainly and its Spanish equivalents in the genre of newspaper opinion discourse. Certainty markers seem to have a presence intrinsic to the opinion genre and, therefore, are expected to “exhibit a certain uniformity across languages” (Dafouz, 2008, p. 110). Whereas the non-correspondence between certainly and ciertamente soon becomes apparent, the results of earlier studies (Ramón, 2009; Carretero, 2012) might well lead to the hypothesis that the PPs sin duda and desde luego realize in Spanish opinion articles the same discourse functions as certainly does in English newspapers. Drawing on naturally-occurring linguistic data from a corpus of English and Spanish opinion texts (C-OPRES), this study (1) investigates the non-correspondence between cognates and (2) explores the aforesaid research hypothesis. Finally, a translation corpus is used (P-ACTRES) to address the complex relationships between seemingly equivalent words, filling in the gaps of the contrastive analysis. The findings reveal a partial overlap between certainly and its Spanish counterparts as epistemic markers or in concessive contexts; whereas there are also significant differences in the distribution of other discourse functions, mainly regarding the emphasizing use of certainly and the grammaticalization of its so-called equivalents in Spanish as textual and/or interpersonal discourse markers.