Here's the set up:
A character has the Two-Weapon Fighting & Improved Two-Weapon Fighting feats, as well as 2+ levels in the Duelist PrC (and therefore has the Precise Strike & Parry abilities). He is wielding a rapier in his main-hand and a dagger in his off-hand.
Here's the question:
Can this character make a full-attack, sacrifice his attacks with the dagger for his Parry ability, and simultaneously gain the damage bonus from Precise Strike to his attacks with the rapier?
I would say yes, since Precise Strike specifically says "a duelist cannot attack with a weapon in her other hand," and by foregoing the attacks granted by TWF & ITWF to use with Parry, he is not actually attacking with a weapon in his off-hand. However, Mr. James Jacobs seems to disagree with me and said to make a thread about it when I brought up the wording.
As an additional note, I think this should work from a thematic stand point, since real world rapier and dagger technique used (uses?) the dagger almost entirely (if not entirely entirely) for parrying.
I don't know one states you can't use your off hand, the other allows you to forgo an attack to gain the Parry
Since you cant really give up an attack you aren’t allowed to use anyways, then you get one ability or the other at a time.
I can certainly understand where you are coming from and could house rule it, but by RAW you have to choose one or the other.
You could however Take at least one level in Monk and Flurry using unarmed strikes with a Cestus (Monks are automatically proficient with a Cestus. A Cestus counts as a light weapon that causes your Unarmed Strikes to deal bludgeoning or piercing. (Tho also as a side note because the Cestus you always deal 1d4 of damage and your Unarmed Strike always deals lethal damage))
Because of the Monks Flurry ability, you can make all attacks granted with one Monk weapon or Unarmed Strike. Simply put you can make all attacks with just one hand (and at a better hit chance since all Monks Unarmed Strikes are counted as Primary and thus take Primary penaltys instead of off-hand penaltys). This allows you to get more attacks than normal with one hand, and still allow you to use both Duelist abilitys.
Though now the Two-Weapon Fighting feats you took are useless if you Flurry.
Because like a lot of things, they are either poorly worded or there are people that try to twist RAW/RAI
The way its worded by RAW you can't use a weapon in your other hand. Really this should have been off-hand IMO, thus eliminating the foot blade as well and making RAW closer to the RAI they meant it to be.
Note: In my first post on here I said off-hand when wording states "other hand"
And if you REALLY want to get into it
"Whenever the duelist takes a full attack action with a light or one-handed piercing weapon, she can elect not to take one of her attacks."
If you notice "a" is a singular, that means when you full attack with "one" weapon.
If you take a full attack action, you declare whether or not your offhand will be participating. You can either not use it and not have any available attacks to forgo for parry. Or you can use it, take the penalty to attacks, forgo the offhand for parry and not benefit from precise strike.
That you gave up the offhand attacks does not mean you were not fighting two handed.