511. The conditional sentence differs from other complex sentences in that the form of the main clause (APODOSIS) is determined in some degree by the nature of the subordinate clause (PROTASIS) upon the truth of which the whole statement depends. Like all complex sentences, however, the conditional sentence has arisen from the use of two independent sentence forms to express the parts of a thought which was too complicated to be fully expressed by a simple sentence. But because the thoughts thus expressed are in reality closely related, as parts of a single whole, the sentences which represent them are also felt to be mutually dependent, even though the relation is not expressed by any connecting word. Thus, speak the word: my servant shall be healed is a simpler and an earlier form of expression than If thou speak the word, etc.

The conditional particles were originally pronouns without conditional meaning: thus, sī (if) is a weak demonstrative of the same origin as sīc, so [sī-ce like hī-ce, see § 215.5], and had originally the meaning of in that way, or in some way. Its relative sense (if) seems to have come from its use with sīc to make a pair of correlatives: thus . . . thus (see § 512.b).

In its origin the conditional sentence assumed one of two forms. The condition was from the first felt to be a condition, not a fact or a command; but, as no special sentence form for a condition was in use, it employed for its expression either a statement of fact (with the indicative) or a form of mild command (the subjunctive). From the former have come all the uses of the Indicative in protasis; from the latter all the uses of the subjunctive in protasis. The apodosis has either (1) the indicative, expressing the conclusion as a fact, and the present and perfect subjunctive, expressing it originally as future— and hence more or less doubtful—or (2) the imperfect and pluperfect subjunctive expressing it as futūrum in praeteritō,¹ and so unfulfilled in the present or past. Thus, rīdēs, mâiōre cachinnō concutitur (You laugh, he shakes with more boisterous laughter), is the original form for the indicative in protasis and apodosis; sī rīdēs originally means merely you laugh in some way or other, and so, later, IF you laugh. So rogēs Aristōnem, neget (Ask Aristo, he would say no), is the original form of the subjunctive in protasis and apodosis; sī rogēs would mean ask in some way or other. In sī rogāres, negāret, the imperfect rogārēs transfers the command of rogēs to past time,² with the meaning suppose you had asked, and sī would have the same meaning as before; while negāret transfers the future idea of neget to past time, and means he was going to deny. Now the stating of this supposition at all gives rise to the implication that it is untrue in point of fact—because, if it were true, there would ordinarily be no need to state it as a supposition: for it would then be a simple fact, and as such would be put in the indicative.³ Such a condition or conclusion [originally past, meaning suppose you had asked (yesterday), he was going to deny] came to express an unfulfilled condition in the present: suppose (or if) you were now asking, he would (now) deny —just as in English ought, which originally meant owed,⁴ has come to express a present obligation.

For the classification of Conditional Sentences, see § 513.

Footnotes