B. THE PROTASIS.  The protasis takes those tenses of the Subjunctive which are required by the Sequence of Tenses.

Examples:—­

DIRECT.  INDIRECT.
si hoc credis, erras, dico, si hoc credas, te errare;
dixi, si hoc crederes, te errare.
si hoc credes, errabis, dico, si hoc credas, te erraturum
esse;
dixi, si hoc crederes, te erraturum
esse.
si hoc credideris, errabis, dico, si hoc crederis, te erraturum
esse;
dixi, si hoc credidisses, te erraturum
esse.
si hoc credebas, erravisti, dico, si hoc crederes, te erravisse;
dixi, si hoc crederes, te erravisse.

a.  Note that a Future Perfect Indicative of the Direct Discourse regularly appears in the Indirect as a Perfect Subjunctive after a principal tense, and as a Pluperfect Subjunctive after an historical tense.

Conditional Sentences of the Second Type.

320.  A. THE APODOSIS.  The Present Subjunctive of the Direct Discourse regularly becomes the Future Infinitive of the Indirect.

B. THE PROTASIS.  The Protasis takes those tenses of the Subjunctive demanded by the sequence of tenses.

Examples:—­

si hoc credas, erres, dico, si hoc credas, te erraturum
esse;
dixi, si hoc crederes, te erraturum
esse;

Conditional Sentences of the Third Type.

321.  A. THE APODOSIS.

1.  The Imperfect Subjunctive of the Direct Discourse becomes the Future Infinitive.

a.  But this construction is rare, being represented in the classical
Latinity by a single example (Caesar, V. 29. 2).  Some scholars question
the correctness of this passage.

2.  The Pluperfect Subjunctive of the Direct Discourse becomes:—­

  a) In the Active Voice the Infinitive in -urus fuisse.

b) In the Passive Voice it takes the form futurum fuisse ut with the
Imperfect Subjunctive.

B. THE PROTASIS.  The protasis in Conditional Sentences of this type always remains unchanged.

Examples:—­

si hoc crederes, errares, dico (dixi), si hoc crederes, te
erraturum esse;
si hoc credidisses, dico (dixi), si hoc credidisses, te
erravisses, erraturum fuisse;
si hoc dixisses, punitus dico (dixi), si hoc dixisses, futurum
esses. fuisse ut punireris.

322.  When an apodosis of a conditional sentence of the Third Type referring to the past is at the same time a Result clause or a quin-clause (after non dubito, etc.), it stands in the Perfect Subjunctive in the form -urus fuerim; as,—­

    ita territi sunt, ut arma tradituri fuerint,[57] nisi Caesar subito
    advenisset, they were so frightened that they would have given up
    their arms, had not Caesar suddenly arrived;

    non dubito quin, si hoc dixisses, erraturus fueris,[57] I do not doubt
    that, if you had said this, you would have made a mistake.