First Type.—Nothing Implied as to the Reality of the Supposed Case.

302. 1. Here we regularly have the Indicative in both Protasis and Apodosis. Any tense may be used; as,—

sī hōc crēdis, errās, if you believe this, you are mistaken;

nātūram sī sequēmur, numquam aberrābimus, if we follow Nature, we shall never go astray;

sī hōc dīxistī, errāstī, if you said this, you were in error.

2. Sometimes the Protasis takes the Indefinite Second Person Singular (§ 356, 3) of the Present or Perfect Subjunctive, with the force of the Indicative; as,—

memoria minuitur, nisi eam exerceās, memory is impaired unless you exercise it.

3. Here belong also those conditional sentences in which the Protasis denotes a repeated action (compare §§ 287, 2; 288, 3); as,—

sī quis equitum dēciderat, peditēs circumsistēbant, if any one of the horsemen fell, the foot-soldiers gathered about him.

a. Instead of the Indicative, Livy and subsequent writers employ the Subjunctive of the Historical tenses in the Protasis to denote repeated action; as,—

sī dīcendō quis diem eximeret, if (ever) anybody consumed a day in pleading; sī quandō adsidēret, if ever he sat by.

4. Where the sense demands it, the Apodosis in conditional sentences of the First Type may be an Imperative or one of the Independent Subjunctives (Hortatory, Deliberative, etc.); as,—

sī hōc crēditis, tacēte, if you believe this, be silent;

sī hōc crēdimus, taceāmus, if we believe this, let us keep silent.

Second Type.—'Should'-'Would' Conditions.

303. Here we regularly have the Subjunctive (of the Present or Perfect tense) in both Protasis and Apodosis; as,—

sī hōc dīcās, errēs, or sī hōc dīxerīs, errāverīs, if you should say this, you would be mistaken;

sī velim Hannibalis proelia omnia dēscrībere, diēs mē dēficiat, if I should wish to describe all the battles of Hannibal, time would fail me;

mentiar, sī negem, I should lie, if I should deny it;

haec sī tēcum patria loquātur, nōnne impetrāre dēbeat, if your country should plead thus with you, would she not deserve to obtain her request?

a. The Subjunctive in the Apodosis of conditional sentences of this type is of the Potential variety.

b. Sometimes we find the Indicative in the Apodosis of sentences of the Second Type, where the writer wishes to assert the accomplishment of a result more positively; as,—

aliter sī faciat, nūllam habet auctōritātem, if he should do otherwise, he has no authority.

Third Type.—Supposed Case Represented as Contrary to Fact.

304. 1. Here we regularly have the Subjunctive in both Protasis and Apodosis, the Imperfect referring to present time, and the Pluperfect referring to past; as,—

sī amīcī meī adessent, opis nōn indigērem, if my friends were here, I should not lack assistance;

sī hōc dīxissēs, errāssēs, if you had said this, you would have erred;

sapientia nōn expeterētur, sī nihil efficeret, philosophy would not be desired, if it accomplished nothing;

cōnsilium, ratiō, sententia nisi essent in senibus, nōn summum cōnsilium majōrēs nostrī appellāssent senātum, unless deliberation, reason, and wisdom existed in old men, our ancestors would not have called their highest deliberative body a senate.

2. Sometimes the Imperfect Subjunctive is found referring to the past, especially to denote a continued act, or a state of things still existing; as,—

Laelius, Fūrius, Catō sī nihil litterīs adjuvārentur, numquam sē ad eārum 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 sī ad centēsimum annum vīxisset, senectūtis eum suae paenitēret, 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 fēlīcitās in sōcordiam vertisset, exuere jugum potuērunt, 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 locō colere dēbēbās, sī ūlla in tē pietās esset, you ought to revere him as a father, if you had any sense of devotion.

b) With both the Periphrastic Conjugations; as,—

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.