The future subjunctive is supposed to be used when a verb or expression requiring the subjunctive in the main clause is in the present or future and refers to a future action. However, the future subjunctive is becoming obsolete, it tends to be replaced by the present subjunctive. The future subjunctive may still be found in writing, such as literature and and legal documents.
The future subjunctive is conjugated much like the -RA form of the imperfect subjunctive: take the third person plural preterite form of any regular, irregular, or stem-changing verb, drop the -RON ending to find the radical, and add the appropriate ending as shown in the box on the right side of this page.
Let's look at a few examples:
yo hablare nosotros habláremos
tú hablares vosotros hablareis
él hablare ellos hablaren
yo tuviere nosotros tuviéremos
tú tuvieres vosotros tuviereis
él tuviere ellos tuvieren
* The yo and él forms of the future subjunctive are identical.
* In the nosotros form, an acute accent is added to the last vowel in the radical.