Rapiers for Fighters Light or One Handed Weapon?

Question

Background:

I'm trying to build a TWF Fighter who focuses on criticals. I was looking for a weapon that would let me leverage power attack and still let me dual wield so proficiency would apply to both and is 18/20.

I came across the rapier which seems to fit the bill nicely. So nicely, that I'm trying to understand if this is a mistake:

One-Handed Melee Weapons:

Rapier |    20 gp | 1d4  | 1d6   | 18–20/×2 —   | 2 lbs.    | P | —

But if I look at the fighter's groups under weapons training:

 Blades, Light: dagger, kama, kukri, **rapier**, sickle, starknife, and short sword.

Question:
What I'm seeing is that I can use the same weapon to power attack with as I can use to twf and only take the -2/-2 penalty. Is that correct?

Here are my two source links:
http://paizo.com/pathfinderRPG/prd/classes/fighter.html#fighter http://paizo.com/pathfinderRPG/prd/ultimateEquipment/armsAndArmor/weapons.html

Answer 1

The “light blade weapon group” is distinct from the “light weapon category” and not all members of the former must be members of the latter, despite what the name would imply. Yes, this is dumb.

So anyway, the rapier is a light blade, but not a light weapon; it is a one-handed weapon. It behaves like a light weapon for the purposes of Weapon Finesse only (and cannot receive 1½ Str to damage if you use two hands with it).

Note, however, that (barring a class feature that says otherwise) you will take large penalties for wielding a one-handed weapon in each hand. Two-weapon fighting requires that one of your weapons (designated “off-hand” during any full-attack in which the two-weapon fighting combat option is invoked) be light to avoid these penalties. Since fighters tend to prefer to stick with a single weapon type because of feats and class features that function only with a single weapon, most two-weapon fighters use dual light weapons. The kukri is the typical 18-20 threat range light weapon. Light weapons can benefit from Power Attack, but not from the extra Power Attack damage you get from using both hands on one weapon (but that wouldn’t work with dual-wielding anyway).

Finally, I just wish to warn you that dual-wielding and critical-hitting builds tend to be on the low end of fighter damage. Two-handed weapons have much greater potential. You should be aware of this going in.