As written, prone and unconscious creatures contribute towards screening, which does not seem quite right to me. They should contribute to screening.
Something about this paragraph does not seem quite right to me. I can't figure out what you are trying to say.
And no, I don't know what the actual definition of 'incapacitated' means in the game. If I had to rule on it I would have it be any combatant that is both prone and has no ability to take actions on their turn.
If paralyzed causes an affected creature to fall prone, then I wouldn't think that they would still cause screening. But that is more because they are prone than because they are paralyzed.
Yeah no that's actually just straight up borked, even past the screening part which I agree intuitively shouldn't apply. The rules regarding moving into/through those creatures squares are also in direct conflict with itself by making a blanket statement denying the player the ability to end their round of movement in a square with another creature at all in the first place.
It does say that you can move through an unwilling creatures space by using Athletics for shove or use Tumble Through but that's probably the least ideal way to go about corpses existing.
I think RAI you should be able to move through and/or share the space with a "willing, unconscious, or dead" creature as per the Prone and Incapacitated Creatures section. You can move through the space of any creature three sizes larger or smaller than you and the larger ones can move through yours. You should also be able to share/move through tiny creatures as they get an exemption.
But for now, you're right, this is either unclear or directly conflicting with itself depending on the sentence and by RAW creatures, whether prone, unconscious, or dead apply screened.
Since you can share the space with them you can logically leave the space. You don't permanently get stuck if you walk into a square with a corpse in it.
As for the screening it mildly makes sense. So a medium person drops prone height-wise they would probably, visually, become small (though still technically and mechanically medium) and assuming they aren't your target that still provides screening. It's effectively anything that hinders your targeting of the enemy provides screening.
incapacitated has it's normal english meaning if it isn't defined in game - they don't (and shouldn't) need to define every single word they use. Paralysed is about as incapacitated as you can get.
If two characters end up sharing a space one of them (GM decides) gets shunted or made prone. 'Accidentally' covers just this sort of situation.
IF you can move into a square and you can move out of a square then you can move through a square - this is self-evident and does not need further defining.
As for screening, that seems perfect to leave up to a GM's call. I can see some situations where some creatures would still provide screening and others where they shouldn't.
Gm's can and should make judgement calls. These are the sorts of situations that are varied enough that some GM discretion is desirable.
incapacitated has it's normal english meaning if it isn't defined in game - they don't (and shouldn't) need to define every single word they use.
To a point, yes. I don't want them to have to write the rulebook in a language that they invented and defined entirely themselves because then I couldn't read it.
But for a term that is being used to describe a condition or status effect, I think it should have more than just the colloquial native language for its definition.
From what I know of the normal English meaning of the word 'incapacitated', a character that has enough Wisdom drain that they are wandering around the battlefield aimlessly could easily be called 'incapacitated'. Even though they are not prone, are not unconscious, are not paralyzed, and may react violently if some other creature tries to move through their space.
Not really, Incapacitate means being unable to act or respond, if you can react violently you cannot be incapacitated.
Paralysed is about as incapacitated as you can get.
At present paralysed creatures have a lot more ability to respond to threats than sleeping creatures. They have better AC and can make Reflex saves.