Detail #393: A Way of Marking Imperatives (and possibly optatives and jussives and the like)

In some languages, there's congruence. Sometimes, this congruence also applies to, say, complements.

Some languages have vocatives!

Now we get the spin: imagine a language with a non-zero marked vocative, and congruence on verbal complements. Now, the next step could be forming the imperative by having an (implicit) secondnd person vocative, and some non-finite verb taking vocative congruence on it.

Next step: specifying the vocative subject would naturally be parsed as third person (or first person) imperative, and those easily become optatives or jussives instead.