Hypothetical statements about possible events
Sí clause: present indicative => Main clause: present indicative, future, ir+a+infinitive, or command
Hypothetical statements about improbable situations
Sí clause: past subjunctive => Main clause: conditional
Hypothetical statements about the past
Sí clause: past perfect subjunctive => Main clause: conditional perfect
Habitual conditions and actions in the past
Sí clause: imperfect => Main clause: imperfect