Future Subjunctive

The future subjunctive is supposed to be used in Spanish 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 Spanish 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:

future subjunctive endings
yo -re nosotros -´remos
tú -res vosotros -reis
él -re ellos -ren

for example...
HABLAR
yo hablare nosotros habláremos
tú hablares vosotros hablareis
él hablare ellos hablaren

TENER
yo tuviere nosotros tuviéremos
tú tuvieres vosotros tuviereis
él tuviere ellos tuvieren

Notes:

* 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.