I originally thought like most others here, but I have changed my mind on how to interpret this.
Take for example a moving ship. We can "assign" the squares to the deck of the ship and not really care that the ship is moving.
But what happens if the ship violently changes direction or stops (which btw, this exact scenario has happened a few times in our games)?
Do the squares move with the creatures? Do the squares stay put and move with the ship? Do the creatures move? What happens?
From what I can tell, there is no "momentum" per se in the game. So, if the ship moves to the right, the creatures stay on their squares and move with it (option a). If the DM adds momentum to the game (option b), the creatures then change squares.
Now, add on to this scenario that some of the creatures are flying.
If you use option a, the flying creatures should not be affect by the movement of the ship. They are not touching the ship. Hence, the ship and its squares move to the right and the flying creatures should stay put.
So, do you give AoOs for the non-flying creatures against the flying creatures (because the flying creatures are no longer in the same squares), or do you give AoOs for the flying creatures against the non-flying creatures (because the non-flying creatures moved away from the flying creatures due to the ship "moving them"). From the perspective of each creature, the other movement type creatures are moving away.
Neither creature initiated this "movement".
If you use option b, both the flying creatures and the non-flying creatures are moving out of their "squares". The flying creatures because the squares of the ship moved under them and the non-flying creatures due to their momentum. Hence, the flying creatures should provoke AoOs by the non-flying creatures and vice versa. Again, from the perspective of each creature, the other movement type creatures are moving away.
Except, the flying creatures did not move. Why are they penalized if they did not move?
Because of these types of issues, I have taken a more restrictive interpretation of the word "Moving" in the AoO rules to mean "the creature uses a move (or full) action to move".
Another way of viewing this is in violent external movement situations, the target is not dropping his guard and he is moving too fast to be AoOed. He is not slowly being moved because he is being pushed on moving on his own, he is being "propelled" from his square.
Note: Bullrushed creatures would still provoke AoOs, but that is a rule of Bullrush. That is not a generic "if someone gets moved" rule.
Take for example a moving ship. We can "assign" the squares to the deck of the ship and not really care that the ship is moving.
But what happens if the ship violently changes direction or stops (which btw, this exact scenario has happened a few times in our games)?
Do the squares move with the creatures? Do the squares stay put and move with the ship? Do the creatures move? What happens?
From what I can tell, there is no "momentum" per se in the game. So, if the ship moves to the right, the creatures stay on their squares and move with it (option a). If the DM adds momentum to the game (option b), the creatures then change squares.
Now, add on to this scenario that some of the creatures are flying.
If you use option a, the flying creatures should not be affect by the movement of the ship. They are not touching the ship. Hence, the ship and its squares move to the right and the flying creatures should stay put.
So, do you give AoOs for the non-flying creatures against the flying creatures (because the flying creatures are no longer in the same squares), or do you give AoOs for the flying creatures against the non-flying creatures (because the non-flying creatures moved away from the flying creatures due to the ship "moving them"). From the perspective of each creature, the other movement type creatures are moving away.
Neither creature initiated this "movement".
If you use option b, both the flying creatures and the non-flying creatures are moving out of their "squares". The flying creatures because the squares of the ship moved under them and the non-flying creatures due to their momentum. Hence, the flying creatures should provoke AoOs by the non-flying creatures and vice versa. Again, from the perspective of each creature, the other movement type creatures are moving away.
Except, the flying creatures did not move. Why are they penalized if they did not move?
Because of these types of issues, I have taken a more restrictive interpretation of the word "Moving" in the AoO rules to mean "the creature uses a move (or full) action to move".
Moving: Moving out of a threatened square usually provokes an attack of opportunity from the threatening opponent.
Another way of viewing this is in violent external movement situations, the target is not dropping his guard and he is moving too fast to be AoOed. He is not slowly being moved because he is being pushed on moving on his own, he is being "propelled" from his square.
Note: Bullrushed creatures would still provoke AoOs, but that is a rule of Bullrush. That is not a generic "if someone gets moved" rule.