If you want to make a trip combat maneuver, do you have to use a weapon with the trip special feature?

No. When making a trip combat maneuver, you don't have to use a weapon with the trip special feature--you can use any weapon. For example, you can trip with a longsword or an unarmed strike, even though those weapons don't have the trip special feature.

Note that there is an advantage to using a weapon with the trip special feature (a.k.a. a "trip weapon") when making a trip combat maneuver: if your trip attack fails by 10 or more, you can drop the trip weapon instead of being knocked prone.

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Editor's Note: The trip special feature also allows you to add the weapon's enhancement bonus when using drag or reposition combat maneuvers, as shown below:

"There is a special exception to the above rules. If you’re using a weapon with the trip special feature, and you’re attempting a drag or reposition combat maneuver, you may apply the weapon’s bonuses to the roll because trip weapons are also suitable for dragging and repositioning (this also means we don’t have to add “drag” and “reposition” weapon properties to existing weapons)."

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