sī Sēstius occīsus esset, fuistisne ad arma itūrī, if Sestius had been slain, would you have proceeded to arms?
sī ūnum diem morātī essētis, moriendum omnibus fuit, if you had delayed one day, you would all have had to die.
Protasis expressed without Sī.
[305]. 1. The Protasis is not always expressed by a clause with sī, but may be implied in a word, a phrase, or merely by the context; as,—
aliōquī haec nōn scrīberentur, otherwise (i.e. if matters were otherwise) these things would not be written;
nōn potestis, voluptāte omnia dīrigentēs, retinēre virtūtem, you cannot retain virtue, if you direct everything with reference to pleasure.
2. Sometimes an Imperative, or a Jussive Subjunctive, serves as Protasis. Thus:—
crās petitō, dabitur, if you ask to-morrow, it shall be given you (lit. ask to-morrow, etc.);
haec reputent, vidēbunt, if they consider this, they will see (lit. let them consider, etc.);
rogēs Zēnōnem, respondeat, if you should ask Zeno, he would answer.
Use of Nisi, Sī Nōn, Sīn.
[306]. 1. Nisi, unless, negatives the entire protasis; sī nōn negatives a single word; as,—
ferreus essem, nisi tē amārem, I should be hard-hearted unless I loved you; but—
ferreus essem, sī tē nōn amārem, I should be hard-hearted if I did NOT love you.
In the first example, it is the notion of loving you that is negatived, in the second, the notion of loving.