The subjunctive is the most complex mood in both the Spanish and the Italian languages. Currently, there are many Italians who use the indicative mood at a colloquial level instead of the subjunctive one (something that does not happen in Spanish, thus it has more vivacity and it is still frequently used). In fact, a future subjunctive form, which was commonly used during the Medieval Period but nowadays has little functional efficiency, has been preserved. This article is aimed at showing the similarities and the differences between these two languages during the Early Middle Ages through the analysis of several chapters of Boccaccio’s Decameron in its first translation to Spanish. To an extent, these resemblances and differentiations could be extrapolated to the present day.