Double (Quality)

You can use a double weapon to fight as if fighting with two weapons, but if you do, you incur all the normal attack penalties associated with fighting with two weapons, just as if you were using a one-handed weapon and a light weapon. You can choose to wield one end of a double weapon two-handed, but it cannot be used as a double weapon when wielded in this way-only one end of the weapon can be used in any given round.