This study deals with mood variability in Spanish and addresses two oft-debated issues. Firstly, do semantic or non-semantic effects best predict mood selection? Secondly, is the Spanish subjunctive disappearing? Focusing on epistemic adverbials of doubt and probability, over 7,000 occurrences of variable mood selection in Argentinian and Mexican Spanish from between the 1850s and 2001 were analyzed using Bayesian mixed-effects logistic regression. Both semantic (epistemic adverbial, aspect, presence of modal auxiliaries, and polarity) and non-semantic (distance between the matrix and the verb, conditional probability of the verb infinitive and of the verb form, and morphological similarity) predictors were analyzed in interaction with real time and variety. The results showed that while both semantics and non-semantics constrain mood selection, the effect of semantics is more limited in terms of scope. Moreover, it is shown that subjunctive usage and productivity have increased over time. I argue that in both varieties change is attributable to concomitant developments in the system of the epistemic adverbials themselves. Importantly, the mapping out of these concomitant changes differs between the two varieties. The developments undergone by the adverbial matrices not only set the stage for change in subjunctive usage, but also bring about cross-varietal divergence in the actualization of change.