2 weapon fighting, "wielding a weapon" advice needed

[Aroth Khashar]

What constitutes "wielding a weapon" for the purposes of the penalties for two-weapon fighting?

If I am carrying two weapons but only attack with one of them, do I incur the penalties on the attack?

What about when I am carrying a shield? Do I always take the penalties as if I am two-weapon fighting, or only if I attempt a shield-bash in that round? Or can I not make a shield-bash (even as an attack of opportunity) unless I take the penalties on my weapon attacks?

[Name Violation]

As long as you're not ATTACKING with 2 weapons to get ADDITIONAL attacks, no penalty.

If you have multiple attacks from a high BAB for example you could attack with right hand, left hand (at usual-5 for Iterative attack) and no additional penalties, full str to both damages.

If you want an extra attack for two weapon fighting THEN you take any penalty on those attacks.

[MrCharisma]

Yup. Only when you make a full attack action, and only when you're getting extra attacks for having 2 weapons.

If you make a full attack with your Hammer (+6) and your Axe (+1) you won't take any penalties because you aren't getting extra attacks.

If you make a full attack with your Hammer (+6/+1) and your Axe (+6) then you would take the penalties, and they apply on all 3 attacks.

If an enemy provokes an Attack of Opportunity (AoO) during the round when you took penalties from TWF then you can make the AoO without penalties since it isn't part of the Full Attack action (even if the AoO somehow happens in the middle of your Full Attack Action).

[Derklord]

There's an FAQ specifically for this. Short version, unless you're using the TWF option to gain an extra attack, you don't suffer TWF penalties, period.