[Varyon]

I'm usually not one for reviving dead threads, but this one piqued my interest when it was linked in the Gritty/Realistic thread. I originally wrote a reply for there, but felt it would be better to post here than derail that thread.

Originally Posted by aesir23

I'd argue (and have), based on my own training, that the real advantage is not multiple attacks or parries, but being able to defend and attack simultaneously.

From what I understand, there's also the benefit that your foe needs to divide his attention a bit because he doesn't know which weapon you'll strike with. That implies Deceptive Attacks might be a little easier to pull off while dual wielding - I'd say so long as you're making a -4/-2 Deceptive Attack or better, you reduce the to hit penalty by 1. So instead of being -2/-1, -4/-2, -6/-3, etc, for a character who is dual wielding this is instead -2/-1, -3/-2, -5/-3, and so forth. The target can opt to focus on one weapon over the other (say, the rapier rather than the dagger) - in this case the weapon being focused on doesn't get the benefit, but the other weapon gets the same benefit as using a reverse grip (any Deceptive Attack imposes a further -1 on the target's defenses, for -2/-2, -4/-3, -6/-4, and so forth). This might not apply to certain attacks - for example, kicks probably shouldn't benefit (a skilled fighter keeps his eyes on the target's leg's already), and neither should shields large enough to grant DB (they're so big you don't need to focus on them).

Originally Posted by aesir23

1. Counterattacks (double time) and Ripostes (single time) are easier and more effective when you can parry with one weapon and attack with another.

I'd say that when using Counterattack and Riposte specifically, attacking with a different weapon than you defended with imposes a further -1 to the target's defense. However, if combined with Deceptive Attack, the benefits from my suggestion above are a bit harder to achieve - you need to be at -6/-3 to get the +1 to hit, or at -4/-2 for the -1 to defense.
Note this also would apply to unarmed attacks - a character who has just Parried a sword strike can use (fully-trained) Counterattack and Deceptive Attack to make an impressive -4/-6 attack (-4/-5 if the target opts to Dodge/Block), unless the target was paying attention to your hand (for -5/-6 or -6/-6 instead).

Originally Posted by aesir23

2. Beats are much more effective because you can attack simultaneously.

Allow characters to learn Dual Weapon Attack in a realistic campaign, even without a relevant Unusual Training Perk, but only have it apply when using a Beat-and-attack.

Originally Posted by aesir23

3. You can perform hard to defend against attacks that would be too risky without a parrying weapon. (Let's call them Committed (Determined) Deceptive Attacks).

Already doable, as noted earlier in the thread. If you feel the -2 for Committed is too harsh, you might be able to justify a Hard Technique that allows a dual-wielding character to buy this off.

Originally Posted by aesir23

1. While training in one or both weapons singly is a helpful foundation, using two weapons simultaneously is a separate and more difficult skill.

GURPS weapon skills, while sometimes overly narrow (like the difference between Shortsword and Broadsword), are actually quite broad in that they allow you to defend against any other sort of weapon (from a knife to a halberd to a biting dragon). Allowing you to use them with or without another weapon in your other hand doesn't seem like much of a stretch there. Personally, I'd either handle it as a familiarity, or I'd have each skill have a favored off-hand skill ("none" being an option, of course), and using it with anything else is at -2.