Sententiae Condiciōnālēs

A conditional sentence (sententia condiciōnālis) consists of two clauses linked into an "if ... then ..." relationship:

Protasis (prōtasis): the "if-clause", introduced by sī "if", nisī "if not / unless", sīn "but if", sī minus, sīn aliter "but if otherwise". The protasis states a hypothesis or condition.

Apodosis (apodosis): the "then-clause", typically a main clause expressing the consequence that follows from the condition.

Latin recognizes three semantic types of condition, distinguished by the speaker's stance toward the condition's reality:

(1) Simple / factual: "if X is/was/will be the case (and I take no position on whether it is), then Y". Both clauses indicative.

(2) Ideal / future-less-vivid: "if X should be the case (a hypothetical, slightly tentative possibility), then Y would be". Both clauses subjunctive (present, sometimes perfect).

(3) Contrary to fact (CtF): "if X were the case (— but it isn't / wasn't), then Y would be". Both clauses subjunctive (imperfect for present, pluperfect for past).

The mood and tense of both protasis and apodosis encode the speaker's stance — Latin's most subtle and rigorous use of mood and tense, demanding precise reading and writing.

Simple (real) conditions are factually neutral: the speaker assumes the protasis may or may not be a fact, but takes no position. Both protasis and apodosis are in the indicative. Any indicative tense may be used; both clauses may have different tenses, and the apodosis may even be an imperative or jussive.

Present-Present: sī hoc dīcis, errās "if you say this, you are wrong". The English translation matches: "if you do, you do/are".

Future / Future-Perfect–Future: sī hoc dīcēs, errābis "if you say (= shall say) this, you will be wrong"; sī hoc dīxerīs, errābis "if you (will have) said this, you will be wrong". Note that English usually uses simple present in the protasis where Latin uses future or future-perfect — Latin is stricter about tense logic. Future-perfect protasis emphasizes that the action is completed before the apodosis begins.

Perfect-Perfect: sī hoc dīxistī, errāvistī "if you (in fact) said this, you (in fact) were wrong".

Imperfect-Imperfect: sī hoc dīcēbat, errābat "if he was saying this (whenever, regularly), he was (each time) wrong".

The apodosis can also be an imperative (sī mē amās, venī! "if you love me, come!"), a jussive (sī tempus est, eat "if it is time, let him go"), or a question (sī hoc vērum est, cūr nōn venit? "if this is true, why does he not come?").

Ideal (future-less-vivid) conditions assume the protasis as a hypothetical possibility — somewhat tentative, not asserted as actual fact. The speaker imagines a scenario without committing. Both protasis and apodosis are in the present subjunctive (or, less commonly, perfect subjunctive for completed action).

This corresponds to the English "if X should..., (then) Y would..." — a tentative, polite, distanced future possibility. The Latin construction is sometimes called the "should-would" condition.

Present-Present: sī hoc dīcās, errēs "if you should say this, you would be wrong" / "should you say this, you would be wrong".

Perfect-Present: sī rēx vēnerit, omnēs gaudeant "if the king should have come, all would rejoice". The perfect subjunctive in the protasis emphasizes that the action would be completed before the consequence.

The line between ideal and CtF is fluid. In direct contrast (sī hoc dīcerēs, errārēs "if you were saying this, you would be wrong" — present-CtF, implying you are NOT saying it), the ideal is less assertive about the protasis being false: it merely raises a possibility.

Contrary-to-fact (CtF) conditions assume that the protasis is not the case. The speaker is explicit that the condition does not (or did not) hold. Two sub-types based on time:

(a) Present CtF — present time, "in fact, it isn't so" — both clauses in imperfect subjunctive. sī hoc dīcerēs, errārēs "if you were (now) saying this, you would (now) be wrong (— but you aren't saying it)".

(b) Past CtF — past time, "in fact, it didn't happen" — both clauses in pluperfect subjunctive. sī hoc dīxissēs, errāvissēs "if you had said this, you would have been wrong (— but you didn't say it)".

Mixed CtF: time of protasis and apodosis can differ. Past protasis + present apodosis: sī hoc dīxissēs, nunc errārēs "if you had said this (in the past), you would now be wrong (in the present, as a continuing consequence)". Present protasis + past apodosis: sī Caesar vīveret, hoc nōn fēcissēmus "if Caesar were alive (now), we would not have done this (in the past)".

The CtF pattern is parallel to the optative subjunctive of unattainable wish: utinam venīret "would that he were coming!" parallels sī venīret "if he were coming"; utinam vēnisset "would that he had come!" parallels sī vēnisset "if he had come".

Negative protasis distinguishes scope:

nisī ("if not / unless") negates the entire condition: nisī vēnissēs, ego vēnissem "had you not come, I would have come" (= "in the absence of your coming").

sī ... nōn negates a single word or element within the condition: sī tū nōn vēnissēs "if YOU (specifically, as opposed to someone else) had not come". This is rarer and emphatic.

sī minus, sīn aliter ("but if not, otherwise") used to introduce an alternative protasis after a positive one: sī potēs, venī; sī minus, mitte litterās "if you can, come; if not, send a letter".

"But if": sīn; sīn autem: marks a contrasted condition: sī ille hostis est, fugiendum est; sīn amīcus, eum salūtēmus "if he is an enemy, we must flee; but if a friend, let us greet him".

Apodosis with passive periphrastic / debeō / oportet / decuit: when the apodosis expresses obligation, necessity, or possibility, the indicative is often retained even where logic would suggest CtF subjunctive: sī hoc nōn fēcissēs, dēbuistī facere "if you had not done this — well, you ought to have done it" (the apodosis "ought to have" stays indicative). This is because the obligation itself is real, even if the action it demands didn't happen.

"Ut"-conditions: rarely, ut + subjunctive can introduce a hypothetical concession ("supposing that"): ut hoc dīcās, nihil mūtābis "supposing you say this, you will change nothing".

Conditional comparisons: quasi, tamquam sī, velut sī, ut sī + subjunctive ("as if"): quasi vēnissēs "as if you had come". Tense follows CtF logic.

For the rules of converting conditions to indirect discourse, see Lectiō XXXII §§ 596-598. Briefly:

• Simple condition's indicative protasis → subjunctive; indicative apodosis → infinitive (with relative tense).
• Ideal condition's subjunctive protasis stays subjunctive; subjunctive apodosis → future infinitive.
• CtF condition's subjunctive protasis stays subjunctive; subjunctive apodosis → special periphrastic -ūrum fuisse (used for both present and past CtF; protasis tense disambiguates).