#half-baked

Grammatical mood, as I understand it, is the way in which the language marks what a sentence (or clause) is doing. There are a few main ones, indicative for statements, imperative for instructions/commands, interrogative for questions, and subjunctive is also pretty common but feels like a bit of an odd one out as it's only for subordinate clauses in certain contexts.

My thought is: what if grammatical mood were an open class, and you could form new moods on the fly using the rules of the grammar? Statements, questions and commands are the main things you can do with a sentence, but there are more. You can apologise, make a promise, form a contract, perform all sorts of ceremonies, legal and informal, etc.. These are lumped into the category of speech acts, things you can do with language beyond merely communicating. You can split up the major categories into finer divisions too. Imperative covers commands, requests and instructions. There are rhetorical and socratic questions in addition to questions where you actually want to know the answer. It's not that you can't already make these distinctions, but if we're adding loads of extra moods we may as well have these as separate options and fold other language features into this mechanism.

Of the languages I know well enough to say, English and French both mark the mood with a combination of word order changes and verb conjugation, Lojban uses particles, and all three have specific words for certain sorts of question that indicate which bit of the sentence is being asked about.

The word order and conjugation methods doesn't generalize very well, so to implement this as grammar, let's have some grammatical particle that transforms a verb into a mood marker, say "mo". Indicative remains unmarked for brevity, and imperative and interrogative both have reduced forms as single words, "mo ask" -> "ma" and "mo request" -> "morc" or something. Then by saying a sentence whose mood is marked with some verb, you are doing the thing that verb describes, to the extent that is actually possible for you to do as a speech act. This is kind of like "hereby" in English, but more of a core feature of the language. Not every speech act needs a separate sentence, so in some cases the mood marker can stand as a complete sentence on its own.

A lot of the time in English, when you're doing a speech act, the form of the sentence is just grammatically you stating that you do that thing, which feels sort of awkward. With a separate mood for every speech act, you can be more explicit.

For apologies, "Mo apologise, I lied to you."

For wedding vows, "Mo take thee as my wife."

Casting a vote (without paper ballots), "Mo vote for X.", or "I prefer X mo vote."

Want to return a faulty item at a shop, and make it very clear that you are invoking your right to do so, as set out in the law? "You refund this, mo legally insist." or if you're feeling fancy, "You refund this, mo invoke Paragraph [whatever] of the [whatever] Act."

For joke purposes, "I'll definitely do that... mo lie."

mo give examples.

The legal examples are where this mechanism feels most fitting to me. I've seen laws and contracts and stuff say things like "If X invokes Paragraph 2.a, Y has to do such and such.", and it just feels a little awkward, like what does it mean for someone to have invoked a rule? The laws define all these acts you can perform that have legal consequences and to do them you just... say you do? It feels weird. Take that "lawyer dawg" example. It is said (this seems like the sort of thing that might be an urban legend, I'm not sure) that a suspect once tried to invoke their right to have a lawyer present when questioned by saying "I want a lawyer, dawg.", and when the police did not respect this request, the judge ruled it legal because the suspect did not request a lawyer properly (a lawyer dog being a nonexistent thing it is nonsense to request).