Abstract: The adverbial phrases capaz que and de repente have undergone processes of change that has made them function as epistemic modal adverbs in certain diatopic varieties of Spanish. Thus, this article studies the diachronic trajectories of these two adverbial expressions in order to enlighten the processes which allowed them to acquire this role, and it attempts to detail their characterization from the point of view of linguistic variation, considering social, contextual and geographical factors.