Indicative or subjunctive

Question

Hi, I'm really struggling with this one, and there are only two possibilities! It's "Aquí tienes 20 euro por si……. dinero para un taxi.", with the options of necesitas and necesitaras. The questions says that the speaker thinks there's a low probability of the money being needed. The correct answer is the imperfect subjunctive, necesitaras. I suppose that it has to be that because the present indicative is not permissible in this structure, but I don’t know why.

Thanks in advance,

Dave

Answer

Hola David

You can use both the present indicative and the imperfect subjunctive here: por si necesitas / por si necesitaras. The reason for marking the present indicative as wrong answer is because in this test-question the hint is stating that "the speaker thinks it is not very probable that he'll need the money", and in that case we'd use the imperfect subjunctive instead of the present indicative, as the lesson is explaining. So, it has that nuance in this instance.

I hope this clarified it.

Saludos

Inma