Can incorporeal creatures inherently "fly"?

[SangoProduction]

I mean, as in, if someone was made incorporeal while only having a land speed, would they have to obey gravity and such (without not falling through, because game logic)?

The incorporeality universal monster rules seems to say absolutely nothing about this.

[Geddy2112]

Yes, although the rules poorly state this. Listed incorporeal monsters gain fly speeds, but all incorporeal monsters can fly.

"Incorporeal creatures pass through and operate in water as easily as they do in air. Incorporeal creatures cannot fall or take falling damage. Incorporeal creatures cannot make trip or grapple attacks, nor can they be tripped or grappled. In fact, they cannot take any physical action that would move or manipulate an opponent or its equipment, nor are they subject to such actions. Incorporeal creatures have no weight and do not set off traps that are triggered by weight."

Because they can pass through water and air equally, they can fly. They cannot fall, and therefore are not subject to gravity. This is supported by the fact they cannot be manipulated by opponents physical actions, or tripped. They do not have weight.

Incorporeal monsters function outside of gravity and therefore can fly. It is not really flight, more that without a body they are not subject to physical forces.

Edit: It turns out there are incorporeal monsters that cannot fly, although logically they should be able to.
The Darnoc (http://www.d20pfsrd.com/bestiary/monster-listings/undead/darnoc/), magnesium spirit (http://www.d20pfsrd.com/bestiary/monster-listings/outsiders/magnesium-spirit/), shadow wolf (http://www.d20pfsrd.com/bestiary/monster-listings/undead/shadow/shadow-wolf-tohc/) and bogeyman (http://www.d20pfsrd.com/bestiary/monster-listings/undead/bogeyman/) (3rd party) are incorporeal and don't have listed fly speeds. Every other incorporeal monster can fly.

[Starbuck_II]

I guess you could call it Airwalk and Airswim, at same time.

[Crake]

If you were to somehow gain an incorporeal state without a flight speed, I would use the rules for the ethereal plane movement, which allows creatures to move in any direction at half their normal speed.

[Florian]

The incorporeality universal monster rules seems to say absolutely nothing about this.

Which is ok. The universal monster rules are more or less setting agnostic and geared toward 2D battle map encounters without regard to setting design. If you use the Ethereal Plane for your setting, than the planar rules and traits will affect how incorporeal creatures will be affected, like giving them a fly speed.

[Firest Kathon]

In my opinion an incorporeal creature without a fly speed could not move at all. They would simply hover in place, unless moved by an external force. While they are not subject to gravity, they also cannot push off from anything to move. However, I also think that all cases of becoming incorporeal without gaining a fly speed would be a rules error (e.g. the sonic form (http://www.d20pfsrd.com/magic/all-spells/s/sonic-form/) spell).

Edited to add: I just want to point out that incorporeal and ethereal are different cases, and ethereal creatures can move in any direction at half speed just fine.

[Wristlet Eater]

If there really are no rules, your group should just decide on their own.

[Firest Kathon]

If you use the Ethereal Plane for your setting, than the planar rules and traits will affect how incorporeal creatures will be affected, like giving them a fly speed.

Just wanted to add on this again, because it is a common misconception: In Pathfinder, incorporeal creatures are not associated with the ethereal plane in any way. They also were not associated in D&D 3.5, with the special exception of Ghosts (http://www.d20srd.org/srd/monsters/ghost.htm), which were creatures existing on the ethereal plane and had a manifestation ability which moved them (partially) to the material plane as an incorporal creature. Pathfinder ghosts (http://www.d20pfsrd.com/bestiary/monster-listings/templates/ghost/)are simply incorporeal creatures (un-)living on the material plane, and are no longer associated with the ethereal plane.