Is it true that the only place where "Si..." is not followed by
a verb in the subjunctive is when "cuando" can be substituted for
- Si sumas dos más dos, tienes cuatro.
- Cuando sumas dos más dos, tienes cuatro.
A verb in the indicative tense works after “si” if talking about
the present/future, but even then the subjunctive could be equally
employed (with the same meaning?):
- Si salgo ahora, llegaré a la hora. If I leave now, I will arrive on time.
- Si saliera ahora, llegaría a la hora. If I were to leave now, I would arrive on time.