Laelius, Furius, Cato si nihil litteris adjuvarentur, numquam se ad earum studium contulissent, Laelius, Furius, and Cato would never have devoted themselves to the study of letters, unless they had been (constantly) helped by them;

    num igitur si ad centesimum annum vixisset, senectutis eum suae
    paeniteret, if he had lived to his hundredth year, would he have
    regretted (and now be regretting) his old age?

3.  The Apodosis in conditional sentences of this type sometimes stands in the Indicative (Imperfect, Perfect, or Pluperfect), viz.—­

  a) Frequently in expressions of ability, obligation, or necessity;
  as,—­

    nisi felicitas in socordiam vertisset, exuere jugum potuerunt, unless
    their prosperity had turned to folly, they could have thrown off the
    yoke;

NOTE.—­In sentences of this type, however, it is not the possibility that is represented as-contrary-to-fact, but something to be supplied in thought from the context.  Thus in the foregoing sentence the logical apodosis is et exuissent understood (and they would have shaken it off).  When the possibility itself is conditioned, the Subjunctive is used.

    eum patris loco colere debebas, si ulla in te pietas esset, you ought
    to revere him as a father, if you had any sense of devotion.

  b) With both the Periphrastic Conjugations; as,—­

    si Sestius occisus esset, fuistisne ad arma ituri, if Sestius had been
    slain, would you have proceeded to arms?

    si unum diem morati essetis, moriendum omnibus fuit, if you had
    delayed one day, you would all have had to die.

Protasis expressed without Si.

305. 1.  The Protasis is not always expressed by a clause with si, but may be implied in a word, a phrase, or merely by the context; as,—­

    alioqui haec non scriberentur, otherwise (i.e. if matters were
    otherwise) these things would not be written;

    non potestis, voluptate omnia dirigentes, retinere virtutem, you
    cannot retain virtue, if you direct everything with reference to
    pleasure.

2.  Sometimes an Imperative, or a Jussive Subjunctive, serves as Protasis.  Thus:—­

    cras petito, dabitur, if you ask to-morrow, it shall be given you
    (lit. ask to-morrow, etc.);

    haec reputent, videbunt, if they consider this, they will see (lit.
    let them consider, etc.);

    roges Zenonem, respondeat, if you should ask Zeno, he would answer.

Use of Nisi, Si Non, Sin.

306. 1.  Nisi, unless, negatives the entire protasis; si non negatives a single word; as,—­