What is the future subjunctive and how was it used?

Question

I've heard that there used to be another tense in Spanish called the "future-subjunctive"

¡A donde fueres, haz lo que vieres!

I've heard the above means in a literal sense, "to where you will go, do what you will see", so I assume that this tense is a sort of subjunctive for things that haven't happened yet.

Is this an accurate description? How was this tense used and how has its usage been replaced in modern Spanish? Why was it deemed necessary to add to the language?

Answer 1

The "simple future subjunctive" is a verbal tense whose function is to express some action that:

• Hasn't happened yet.
• There's some possibility that it will happen in the future.

These features aren't expressed by any other verbal tense in a direct way, and in order to approach to it, they should need some additional adverbs or just simply use the context of the sentence.

Due to the features of this verbal tense, it is widely used by legal texts and documents, cause they need to be as precise and concise as possible (among other requirements, of course).

It is not widely used in common speech, and is seldom used in novels and other written texts.

Sometimes it's confused with "simple preterit subjunctive" (pretérito simple de subjuntivo) because they have similar endings:

• Trabajare (simple future subjunctive)
• Trabajase / Trabajara (simple preterit subjunctive)

As an example of the importance of this verbal tense may be expressed comparing the following sentences (example taken from http://www.delcastellano.com):

1. El que matare al rey [...] será castigado [...]
2. El que mate al rey [...] será castigado [...]

In the first one, we may see clearly that the fact of the King being killed is not sure, it's just a possibility. But in the second one, we may read that the king will be killed, for sure sooner or later.

I've used "simple future subjunctive" (futuro simple de subjuntivo), because there is another verbal tense called "perfect future subjunctive" (futuro perfecto de subjuntivo) that is formed with the help of the verb haber:

• Trabajare (simple future subjunctive)
• Hubiere trabajado (perfect future subjunctive)

Answer 2

Future subjunctive is deprecated but not unused. See for example legal documents.

If you are writing a legal statement for the winner of the lottery you could write something like:

Aquel que haya comprado la boleta cuyo número es el número resultado del sorteo, será el ganador.

Wich translates: one who buy the ticket with the winner number will be the winner.

I don't see a strictly need that force its use but again, its commonly used (to clarify and enforce a conditional future).