Can an incorporeal creature occupy the same square as a normal creature? Does it matter if it's during a move (moving through another creature) or at the end of the move (stopping in the other creature's space)? How about another incorporeal creature, is that case different?
Several things cast doubt on the conclusion being obvious. The SRD says incorporeal creatures cannot be Tripped or Grappled, nor can they perform those actions. It also says they are weightless. When it says
In fact, they cannot take any physical action that would move or
manipulate an opponent or its equipment, nor are they subject to such
I understand that to mean Bullrushed and Overrun as well, even though the book only mentions Trip and Grapple as examples. So they can't use those methods of moving through an opponent's square.
It's also not clear if an incorporeal creature can pass through a square containing another creature without Tumbling (whether or not it provokes AoOs when it does).
All together, these leave open the question of under what conditions one corporeal and one incorporeal creature, or two incorporeal creatures, can occupy the same space, since that's usually disallowed except via one of these maneuvers or skill checks. It would seem strange for a corporeal creature to have no options to move into/through another creature's space, since it seems like the main point of incorporeality is to be able to move through things. Does an opponent provide an impassable obstacle for an incorporeal creature?
Can incorporeal creatures occupy the same space as another creature either during a move or at the end of a move, and if so, how?