tense for subordinate clause

Question

I have a question about the sentence: "Le dare el dinero que le debo por si acaso se me olivida despues."  If I understand, this sentence expresses the idea that the speaker feels that it is fairly likely that they will forget.  If they thought that it was unlikely that they would forget, then the conditional clause would say "..se me olvidara".  So myy question is: What if the main clause were in el preterito indefinido (Le di el dinero...)?  Would the conditional clause still need to be "...se me olvidara"?  If the speaker considers the condition in the subordinate clause to be less probable, the conditional clause would use the imperfecto do subjunctivo (...se me olividara) whether the main clause refers to a future action or a past action?  Is this correct?Sorry, I don't know how to type accents.

Silvia Piriz · Accepted Answer

Hola Steven S.
Great question! In the sentence "Le daré el dinero que le debo por si acaso se me olvida después", the main clause (Le daré el dinero...) uses the futuro simple, and the subordinate clause (por si acaso se me olvida después) uses the presente de indicativo, because the speaker considers forgetting to be a likely or plausible possibility.
If you change the main clause to the pretérito indefinido—"Le di el dinero que le debía por si acaso..."—the tense of the subordinate clause depends on how likely or hypothetical the speaker perceives the forgetting to be. If the speaker considers forgetting likely, the pretérito imperfecto de indicativo would be used: "por si acaso se me olvidaba después." However, if the forgetting is seen as less likely or hypothetical, the pretérito imperfecto de subjuntivo would be used: "por si acaso se me olvidara después."
The key point is that the choice between indicativo and subjuntivo in the subordinate clause depends on the speaker’s perception of the likelihood of the condition, not whether the main clause refers to a future or past action.
The indicativo is used for plausible or likely conditions, while the subjuntivo adds a hypothetical or tentative tone.
For example, with the main clause in the futuro simple: "Le daré el dinero por si acaso se me olvida después" (likely) vs. "Le daré el dinero por si acaso se me olvidara después" (unlikely).
Similarly, with the pretérito indefinido: "Le di el dinero por si acaso se me olvidaba después" (likely) vs. "Le di el dinero por si acaso se me olvidara después" (unlikely).
I hope this clears things up! Let me know if you have more questions. 
Hasta pronto
Silvia