Si no llegas a las seis empezamos sin ti.
If you don’t arrive at six we’ll start without you.16.1.1.2 (p. 59)
51.1.2 Si+ present + present/future
The verb in the si-clause is in the present, no matter whether the action conveyed
by it refers to the present, e.g. si es como usted dice... , ‘if it is as you say.. .’, or
to the future, e.g. si llueve mañana.. .’, ‘if it rains tomorrow’. The verb in the other
clause may be in any appropriate tense, usually the present or the future.We use this construction with si, ‘if’, when we want to express uncertainty with regard
to something, as in:
Si es como usted dice estamos cometiendo un grave error.
If it is as you say we are making a grave mistake.
Si es como usted dice cometeremos un grave error.
If it is as you say we’ll make a grave mistake.
Si le duele tanto es/será mejor llamar a un médico.
If it hurts him/her so much we’d better call a doctor.51.1.3 Si+ verb in the past + present/future
To express doubt with regard to something in the past, for example, Si ha llegado ... ,
‘if he/she has arrived.. .’, we use this construction with the verb in the if-clause in
the perfect, preterite or imperfect, followed by the main clause with a verb in the
present or future.
Si ha llegado hablaré con él.
If he has arrived I’ll speak to him.
Si llegó sólo ayer no lo llamaré hasta mañana.
If he only arrived yesterday I won’t call him until tomorrow.Si estaba tan cansada será mejor no molestarla.
If she was so tired we’d better not bother her.51.1.4 Si+ present + imperative
Si necesitas dinero pídemelo.
If you need money ask me.
Si tenéis tiempo no dejéis de ir.
If you have time don’t fail to go.16.1.1.6 (p. 62)
EXPRESSING CONDITIONS 51.1