Spanish Future and Future Perfect Subjunctives
The future subjunctive and the future perfect subjunctive are all but dead in modern Spanish. They live on in proverbs and in legal documents. Very rarely, they find their way into oratory, sermons and the editorial page, but even then, it usually appears in the form of a well known phrase either in legal or proverbial use.
If you studied Spanish, even for all four years of high school and possibly even all four years of college, and even became reasonably proficient, there is still a good chance you have never learned these two subjunctive tenses. If you ever read literature from prior to the nineteenth century, it is highly likely that you have come across it. You might have thought it was a typographical error unless your professor or a footnote told you otherwise.
This short article is for those who are already familiar with the subjunctive and have been able to follow this up to know. If not, you are advised to wait until you do before studying with this article, so you don’t become confused. If you want to master the subjunctive in modern Spanish, then consider purchasing Practice Makes Perfect: The Spanish Subjunctive Up Close. I developed the book over several years because I was consistently dissatisfied with textbook explanations and their order (or lack of order) in presenting this very important feature of the Spanish language. Even though the Spanish Royal Academy of the Language is correct and thorough on every grammatical point, their entries on the subjunctive were not meant for non-Spanish speakers. So, if you want to really learn it, you now can have a book that will help you.
The uses of the future subjunctive were eventually taken over by the present subjunctive and those of the future perfect subjunctive were taken over by the present perfect subjunctive. The base or stem of the future subjunctive is formed exactly as the imperfect subjunctive, that is, from the third-person of the preterite. Thus, the base of the future subjunctive of tener is tuvier- just as it is also the base of the imperfect subjunctive. From here, the only difference between them is that the imperfect subjunctive proceeds with an a + personal endings and the future subjunctive proceeds with an e + the personal endings. The yo form of the future subjunctive is tuviere, tú is tuvieres, and so forth.
Using tener to show the formation of the future perfect subjunctive, remember that the past or passive participle of tener is unchanged –tenido. It is the auxiliary or helping verb haber which will show the tense and mood. Just as the pluperfect subjunctive is formed from the imperfect subjunctive of haber + the past participle (yo: hubiera tenido), the future perfect subjunctive requires the future perfect of haber + past particle: yo hubiere tenido. One example of proverbial usage still heard in ordinary speech in many place is sea lo que fuere (come what may, or literally, "let whatever happens later, be").