2091. A conditional period in which the non-occurrence of the action is
implied takes the imperfect or pluperfect subjunctive both in the
protasis and in the apodosis. The imperfect usually denotes present or
indefinite time, and the pluperfect denotes past time.
For the present subjunctive in such conditions, see 2075.
2092. The imperfect sometimes denotes past time (1559). When future time
is referred to, the protasis is usually in the imperfect of the
periphrastic future, commonly the subjunctive, but sometimes the
indicative (2108).
2093. The apodosis is very rarely in the present subjunctive (2098). The
periphrastic future is sometimes used, commonly in the indicative (2097,
2100).
(1.) PROTASIS IN THE IMPERFECT SUBJUNCTIVE.