I’ve been somewhat obsessed lately with the demise of the optative mood in both Italic (the parent language to Latin, among others) and in koine Greek. For some reason, it strikes me as very strange that both languages would lose the optative. Italic, of course, lost the optative completely, replacing it, to a certain extent, with the imperfect subjunctive (see my overview of that change here). Greek, however, didn’t technically lose the optative, but it replaced the optative with the subjunctive in most every case; in other words, it functionally, though not formally, lost the optative mood in terms of usual means of expression.
As I’ve reported, the old Proto-Indo-European subjunctive, along with the old desiderative, became the future tense in Latin, while the optative mood stepped in to fill the empty shoes that the old subjunctive left when it switched uses. Here’s the interesting part about this change: “The [Proto-Indo-European] subjunctive seems to have referred to a future event anticipated with some slight reservation on the part of the speaker — the equivalent of ‘I suppose’ or ‘in that case'” (Sihler 592), and in very old Sanskrit (a cousin to Latin), the subjunctive usually just acts as a simple future. In other words, it takes no great stretch of the imagination to see how the subjunctive could get watered down in Italic (and thus Latin) to the point where it is solely a future tense. That left only the optative for expressing counter-to-fact statements, and the optative form became, by default, the subjunctive.
Here’s where it gets interesting. In Greek, the subjunctive did not get watered down at all. In fact, by the time of the New Testament, the subjunctive had grown in strength to the point where it replaced the optative in most cases, except in prayers, strong affirmations or condemnations, stock phrases, and the like. So, while in Italic, the optative replaces a highly weakened subjunctive, Greek sees just the opposite: a strengthening subjunctive takes over the optative. However, both phenomena have the same effect, namely that, in both languages, the subjunctive is the primary mode for expressing something counter to fact.
Work cited: Andrew L. Sihler, New Comparative Grammar of Greek and Latin (new York; Oxford: Oxford University Press, 1995), 592-600.