This is the issue:
ka suo = "eater"
ko suo = "eating"
ka pa suo = "food"
ka ko suo = "meal"
I can't help feeling that this is way too logical and not nearly natural enough. Shouldn't "food" be a base morpheme? And "eatee" is not necessarily the same thing as "food," anyway.
It gets even more ridiculous with, for example, kaka: ka pa kaka = "the thing shat" = "poop." Poop is one thing that should, incontrovertibly, be monomorphemic.
I was getting around this conceptually before by imagining pa- as a bit of derivational morphology that one would just get used to, like -enie, etc. in Polish. So there's súo and pasúo. I just can't seem to get past, though, the fact that I don't like this and don't feel it's typologically sound.
If the verb lalu is "sing," shouldn't the noun be "song" rather than "singer?" But Koa has no copula, so you end up with problems like
le Mia i lalu = "Mia is a singer" or "Mia sings" or "Mia is a song."
One could possibly manage this by additional particles/morphology:
le Mia i (a) láluma = "Mia is a singer"
le Mia i (ua) lalu = "Mia sings"
le Mia i a lalu = "Mia is a song"
In the past, though, we've specifically disallowed this X i a Y construction, and I'm uncomfortable with it. For one thing, is a really the best article? And secondly, I think there's an unreasonably likelihood of confusion with ia.
What about when the result of the action and a single instance of the action are both word-worthy concepts? Going back to excrement as a concept that tends to be fluidly expressed cross-linguistically, how do we do (A) "that was a good shit" and (B) "that's some good shit?" Currently it would be something like
A: vo ko kaka koa
B: vo pa kaka koa
I can't help feeling like B ought to be vo kaka koa. What, then, would A be?
In this particular case, one could perhaps circumvent the whole problem by saying kaka is a noun, and have some kind of helper verb: tei kaka = "make/do poop," etc. I don't know that this could work for lalu, though.
What about "theft" vs. "stealing?" Ko iune i pua = "stealing is bad" seems straightforward enough, but what about "the theft of the money?" Ka ko iune ka vatu? Is that really what we want? What about "The theft of the money was known to everyone in the town?" We'll try it without the passive first:
Poka ne ka lina i ilo ka ko iune ka vatu
Ugh. Let's try again:
Poka ne ka lina i ilo ko ka vatu i si pa iune
Pa ilo ko ka vatu i si pa iune o poka ne ka lina
Well, aside from the fact that this last sentence is ambiguous between our intended meaning and "it was known that the money was stolen by everyone in the town," it does seem that rephrasing the clause works best. Can I do this with a shorter phrase, e.g. Nu ma puhu pe ko si pa iune ka vatu or nu ma puhu pe ko ka vatu i si pa iune? I don't see why not.
Er...does this help us, though? I'm still not sure about the "food/meal" problem.
Okay, thoughts: (A) There's a big difference between pa suo "food" on the one hand, and ma pa suo "the guy being eaten" on the other hand. Maybe that solves that part. (B) Since I seem to have no problem with Esperanto manĝaĵo and kakaĵo, and Polish jedzenie, there's really no reason why I should balk at pa suo typologically. (C) Using a dummy verb (tei kaka, etc.) will fix a bunch of this, and I should finally decide on what that's going to be. (D) Do I really have to worry that much about kaka meaning both "poop" and "to poop?"
As a matter of fact, I've been thinking about valence recently and the fact that I think it might be best to be a bit loose about the whole active/passive distinction. Thinking of English, for instance, there's no particular reason that an "opener" couldn't be agent (doorman), patient (door), or instrument (key) all at the same time or as needed in context. The fact that we don't feel the same flexibility with e.g. "singer" isn't because of any inherent problem with the concept, but just an accident of custom.
Maybe pa can be like many of the other particles: always acceptable, but not required unless that part of the meaning is being stressed or its absence would cause unreasonably ambiguity. In the same way u could be pressed in to use to mean "accentedly active": so, like, ka u ma suo vs. ka ma pa suo, etc.
P.S. Okay, wait, though: how do we cope with "You can eat it, but I wouldn't call it food?" Ta te pa suo, ala ni na lule ko ta pa suo? I mean, what this is basically saying literally is "it can be food, but I don't think it's food." Does that make sense? I really don't know at this point.