Two weapon fighting, but using offhand for AoO only

Question

Okay, so we are switching DMs to give myself a break from it, and I'm rolling up a level 8 bard to support the current group.

I'm going with whip mastery and improved/Greater Trip and everything else involved, plus the usual bard stuff.

So, I'm not worried about doing damage, I want to help control the battlefield and buff my allies, So, provoking AoO for my allies from Greater Trip attempts seems like a good idea, maybe it's not, but I'm gonna try it.

My question is this, if I carry a main hand weapon (rapier, shortspear, etc; not completely decided yet) and just hold a whip in my offhand, I understand that I won't incur TWF penalties because I'm not actually attacking with my off hand weapon, right?

If that is true, then a follow up question/scenario is this: If I only use the whip during AoO, will this incur TWF penalties on either my main hand attacks or the off hand?

I have a player that suggests that since I am not attacking with the whip, the whip doesn't actually threaten any spaces, therefore I cannot take advantage of AoOs with the whip. (I think I'm clear on the threat range and attack range of whips, with my feat selections I'll have a 10ft radius of threat [including adjacent squares], with a 15ft reach for attacks.)

Answer 1

My question is this, if I carry a main hand weapon(rapier, shortspear, etc. Not completely decided yet) and just HOLD a whip in my offhand, I understand that I won't incur TWF penalties because I'm not actually attacking with my off hand weapon, right?

This is correct.

"If you wield a second weapon in your off hand, you can get one extra attack per round with that weapon. You suffer a –6 penalty with your regular attack or attacks with your primary hand and a –10 penalty to the attack with your off hand when you fight this way. You can reduce these penalties in two ways. First, if your off-hand weapon is light, the penalties are reduced by 2 each. An unarmed strike is always considered light. Second, the Two-Weapon Fighting feat lessens the primary hand penalty by 2, and the off-hand penalty by 6." PFSRD

If simply holding a weapon in an off-hand were to trigger the Two-Weapon Fighting rules, then many characters who wield shields, carry torches, or hold a pole would be subject to those penalties without utilizing the weapon to attack.

If that is true, then a follow up question/scenario is this: If I ONLY use the whip during AoO, will this incur TWF penalties on either my main hand attacks or the off hand?

No.

"If you wield a second weapon in your off hand, you can get one extra attack per round with that weapon. You suffer a –6 penalty with your regular attack or attacks with your primary hand and a –10 penalty to the attack with your off hand when you fight this way. You can reduce these penalties in two ways. First, if your off-hand weapon is light, the penalties are reduced by 2 each. An unarmed strike is always considered light. Second, the Two-Weapon Fighting feat lessens the primary hand penalty by 2, and the off-hand penalty by 6."

Taking an Attack of Opportunity is not an extra attack in the round - it is an attack generated by the opponents movements or actions.

I have a player that suggests that since I am not attacking with the whip, the whip doesn't actually threaten any spaces, therefore i cannont take advantage of AoOs with the whip.

Provided your whip using character has the feat Improved Whip Mastery, (which I do assume, given your statement: "I'm going with whip mastery and improved/Greater Trip and everything else involved, plus the usual bard stuff") then yes, you are able to threaten an area with your whip.

"You threaten all squares into which you can make a melee attack, even when it is not your turn." PFSRD

Even when you choose to not take an Attack of Opportunity, the square is still threatened.

Further, even if you did attack with both of your weapons in a Full Attack action, you would not suffer the Two-Weapon Fighting penalties on Attacks of Opportunity, per the PFFAQ.

"Two-Weapon Fighting: If you use this on your turn to attack with two weapons, do you also take that penalty on attacks of opportunity made before the start of your next turn?

No. The penalties end as soon as you have completed the full-attack action that allowed you to attack with both weapons. Any attacks of opportunity you make are at your normal attack bonus."

Answer 2

You get the penalty for getting the extra attack with your off-hand weapon, not for holding a second weapon, not for using a second weapon, not for switching between the two. If you choose not to take that extra attack, you take no penalty.

I think the question has been answered, but let me nerd out a bit. :) This is all based on my understanding. Correct me if I'm wrong.

Consider this: Your high-level character has six arms. Three of them hold a single-handed weapon. Ie. sword, axe, mace. In your other three hands you hold a single weapon that can feasibly be wielded with three hands, maybe a spear with reach. Your base attack bonus gives you three attacks.

On your turn, you can attack with whatever weapon you choose per attack. You can use the same weapon three times, three different weapons, or any combination AT NO PENALTY because you are not getting any extra attacks. Assume you use the axe, sword and mace. Then, when not on your turn, each of your wielded weapons threaten squares as normal, regardless of if you attacked with them or not. You CAN make AoOs at range with the three-handed spear at no penalty. At no point did you get an extra attack, either in your full attack or as an AoO.

On the other... HAND... Let's say your low-level character has only one hand due to an amputation and only one attack based on your base attack bonus. You wield a one-handed double-bitted axe, let's say. Your DM agrees that you can make an attack with both bits in one attack. This would get the two-weapon fighting penalty, because you get an extra attack. It wouldn't matter the number of hands used or the number of weapons.

You get the two-weapon fighting penalty for the extra attack, not what you hold or what you are attacking with.

Answer 3

No.

"If you wield a second weapon in your off hand, you can get one extra attack per round with that weapon. You suffer a –6 penalty with your regular attack or attacks with your primary hand and a –10 penalty to the attack with your off hand when you fight this way." PFSRD. Notice that it doesn't say "If you choose to make an extra attack, you suffer a penalty". You suffer the penalty if you are wielding the second weapon, i.e. holding it ready to use in an AoO. Think of the penalty as representing how you can't throw your whole body into the rapier thrust if you also want to keep your footing for the whip attack.

Unless you don't need your Move action

Pathfinder is very happy to let you change what you're holding in your hands during your turn. By way of comparison, if you're wielding a quarterstaff two-handed, you can switch to wielding it one-handed while you cast a spell, then switch back before the end of your turn, since both are free actions (search for "two-handed" in my PFSRD link). In your case, it's a Move action to draw a weapon, or to pick it up from the ground (and picking it up from the ground provokes an AoO of its own). It's another Move action to sheathe a weapon, and a free action to drop it.

So in the first round of combat, if you start next to an enemy, you can attack them without wielding the whip, then draw your whip as a Move, ready to make AoOs. Next turn, you have two options: you can sheathe your whip as a Move, then make an attack with no penalty, but not be able to make AoOs after this turn, although next turn you can. Alternatively, you can drop your whip as a free action, attack, then pick up your whip this turn, and attract an AoO of your own.

Edit: It's ambiguous

The rules say "When you fight this way". It's not really clear whether "fight this way" means "wielding two weapons" or "making an extra attack". On the one hand, the penalty for two-handed fighting doesn't affect your AoO, so it would make some sense if it was the latter. On the other hand, you're still using your whip for the purposes of fighting if you're wielding it without making an extra attack. The Move action to start "wielding" a weapon might not just mean taking it off your belt, it might also mean adjusting your footing so you're ready to attack with the whip. Honestly, if I was DMing this, I'd rule wielding was fighting, just because it gives you more options to consider during a combat (when do you draw your whip? If you pick up your whip off the ground and draw an AoO, does that let someone else do something cool without being attacked?) But YMMV, and in particular, YDMMMV.