Why use subjuntivo en this type of sentence

Question

Hello!Why use subjuntivo vs indicativo in this sentence? Una vez que ustedes firmen, no hay marcha atrás. I can’t imagine using subjuntivo, or maybe I’m just thinking of it as a real factual warning vs something hypothetical that I can’t imagine in real situation.

Silvia Piriz · Accepted Answer

Hola Max y David
Great question! The use of the subjunctive in the sentence "Una vez que ustedes firmen, no hay marcha atrás" is due to the element of anticipation and the idea of a future action that has not yet occurred.
In Spanish, when using expressions like "una vez que" (once), "cuando" (when), "hasta que" (until), and similar phrases, the subjunctive is often required if the action has not yet happened. This is because these expressions introduce a dependent clause that refers to a future or hypothetical scenario.
In this particular sentence, the signing (firmen) is an anticipated event. Since it has not occurred yet, Spanish uses the present subjunctive to reflect this uncertainty. Once the signing is complete, the outcome ("no hay marcha atrás" - there is no turning back) becomes a definitive statement in the indicative mood.
In contrast, if you were talking about a past event, you would use the indicative: "Una vez que firmaron, no hubo marcha atrás" (Once they signed, there was no turning back).
David’s comment also brings up a good point. In English, we often use the present tense in similar future-anticipating expressions, which can feel more like the indicative, but in Spanish, this is a classic scenario for the subjunctive.
I hope this clarifies the use of the subjunctive in this type of sentence! Let me know if you need more examples or if anything is still unclear.
Saludos
Silvia

David Lips · Answer

That's an interesting point and I suppose it's not really 'hypothetical' but rather 'anticipated'

It's the same in English - 'Once you sign' we use the present tense to refer to a future event so that is effectively an English subjunctive mood.

Una vez is interesting because the synonyms of 'once' are 'when' and 'after' but if you type the sentence into Google Translator using them you sometimes get indicative.

Max Sakalouski · Answer

Thank you both Silvia and David for your explanation! Seems like I disregarded the language structure which clearly indicated the need of using subjunctive.