Latin conditional clauses

Conditional clauses in Latin are clauses which start with the conjunction sī 'if' or the equivalent.^[1] The 'if'-clause in a conditional sentence is known as the protasis, and the consequence is called the apodosis.^[2]

Conditional clauses are generally divided into three types: open conditions,^[3] when the truth of the condition is unknown ('if it is true that...'); ideal conditions, in which the speaker imagines a situation or event which might occur in the future ('if this were to happen...'); and unreal conditions, referring to an event or situation in the present or past known to be contrary to fact ('if it were true that...'). These three are also sometimes referred to as Type 1, Type 2, and Type 3 respectively.^[4] Open conditional clauses in turn can be divided into particular and general.^[5]

Open conditional sentences generally use the indicative mood in both protasis and apodosis, although in some general conditions the subjunctive mood is used in the protasis. Ideal and unreal conditionals use the subjunctive in the protasis, and usually they also use the subjunctive in the apodosis, though sometimes the indicative may be used. Conditional clauses of comparison ('as if') also use the subjunctive mood in the protasis.

Conditional clauses sometimes overlap in meaning with other types of clause, such as concessive ('although'), causal ('in view of the fact that'), or temporal ('whenever').

The conjunction sī is only rarely used in classical Latin to introduce indirect questions, although this usage is found in medieval Latin and is common in Greek and in modern Romance languages such as French and Italian. The use of 'if' to make a wish, found in ancient Greek, is not usual in Latin, except sometimes in poetry.