The Spanish future subjunctive demonstrates how linguistics can inform modern language policy. The FS is described as an archaism to be eliminated from contemporary legal texts. We analyze a corpus of over 3000 tokens of the FS in Spanish legal texts dated between the 13th and 16th century. The FS has two functions in legal discourse. The casuistic function allows for indicating paradigmatic subordination; the forwarding function introduces new information. Our quantitative results suggest an increase in the usage frequency of (...) the FS in legal discourse, where an inverse trend appears in other genres. As shown by a linear regression analysis, the FS started appearing significantly closer to the beginning of the law article, indicating an increase in the forwarding function in time. In view of our results, reformers of legal Spanish should consider the functions of the FS in legal discourse when advising its suppression. (shrink)