The third edition of the D&D system offers the following rules for Two weapon fighting:
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.
These penalties can be offset if the weapon wielded in the off hand is light, and if the character takes the Two Weapon Fighting Feat. The rules accurately reflect the fact that two weapon fighting is a difficult task that requires training to be able to do well. However the explicit assumption here is that the primary purpose of dual wielding was to gain the capacity to attack more frequently. This would be an advantage both in a battlefield encounter and in a one on one combat encounter… that is if the assumption were sound.
However, though I am no expert in that art of sword fighting from what I can tell this assumption does not seem to be sound. Scholagladitoria has a nice gloss on the topic of historic dual wielding techniques over on his Youtube channel. He points out that while historic examples of dual wielding techniques can be found, it was not a popular or widely utilized style of fighting. The benefit of dual wielding was not that it allowed a combatant to attack more often but rather that it provided better protection against attacks. Typically a combatant is just as quick with one sword as with two. Having an additional sword does however allow an additional instrument to parry with. That said, a shield offers the same general benefit to defense, and does a better job of it as well. This is especially true on the battlefield where a shield can provide cover from missile attacks. What’s more, the coordination needed to dual wield effectively takes a fair amount of practice to achieve, while the same is not true of the sword and board style.
Dual wielding does have an advantage over and against the sword and board style however: it allows more options for simultaneously attacking and defending. A combatant can parry with one hand while attacking with the other. It may also be that dual wielding offers a slight advantage in landing an attack against an opponent: the defender must split their attention to protect against an attack that could come from either weapon, and this makes it more easy to land a blow.
So with this in mind here is a proposal for amending the Two Weapon Fighting rule to better comport with the actual world:
If you wield a second weapon in your off hand you gain a +1 deflection bonus to your armor class but suffer a -2 penalty to attacks made with either weapon.
Further training in the style of dual wielding (e.g. taking the Two Weapon Feat tree progression) would result in an increase to the bonus gained to deflection and a decrease to the attack penalty (at higher stages even offering a bonus to attacks).
Training might also enable a dual wielder to gain an additional attack under certain circumstances, such as when she simultaneously parries and attacks. Here are two different suggestions for modeling this: (a) whenever the opponent makes a melee attack roll that is unsuccessful by a certain margin (say by 5 or more) the dual wielder automatically gains an additional attack; (b) whenever the opponent makes a melee attack against a dual wielder, prior to actually making a die roll, the dual wielder may indicate that she wishes to attempt a ‘riposte’, parrying with one hand while simultaneously thrusting with the other. While making a riposte maneuver a dual wielder loses the deflection bonus gained by the offhand weapon but gains an additional attack with their primary weapon. Both attacks are resolved simultaneously.
I’m considering implementing something like the above amendment (haven’t yet decided between a and b) within the revised 3e rule system I’m working on. Thoughts?
ars phantasia 
Potential issues I see:
*Reduction of choices that directly affect how the character plays for melee characters. Right now, you can choose between few attacks with higher damage and lower defense (two-handed), few attacks with lower damage and higher defense (sword-and-board), or many attacks with lower damage and lower defense (dual-wielding). From my understanding of your system, you would be able to choose between few attacks with higher damage and lower defense (two-handed), few attacks with lower damage and higher defense (sword-and-board), or few attacks with lower damage and higher defense (and you have to spend feats to not be penalized and only if you spend even more feats can you be something other than a sword-and-boarder with a feat tax — dual-wielding).
*Hinders certain melee archetypes much more than others. A dual-wielding fighter probably isn’t going to care too much either way. A dual-wielding rogue or any other character that depends on extra damage dice is going to care A LOT. While damage output is certainly not the be-all and end-all of D&D, it is quite important if you want to survive combat and, in my experience, can be a major factor in perceived power balances/imbalances between characters. That rogue with his lower strength is going to be seriously hurting on his damage output if he can’t attack more times to get his extra damage dice multiple times a round (at least on the rounds where he can line everything up right).
*Once the options for extra attacks come on board, they happen during the opponent’s turn, which can be a pain for initiative and brings up some questions. Will attacking during the opponent’s turn affect the dual-wielder’s available actions during her turn? Will it take the place of her attack of opportunity? (Hello, Combat Reflexes, yet another feat you’ll be really, really wanting.)
With the first option, is it a valid strategy for a dual-wielder to pump her AC as high as possible, walk into the middle of a group of enemies, and collect as many free attacks as possible on their turn? Or pump her AC and deliberately provoke as many attacks of opportunity as possible on her turn? (Which would actually be hilarious and I kinda want to play a character with a death wish now…)
With the second option, can two duel-wielders get into a never-ending riposte loop before they even roll the dice? (I attack! I riposte! I riposte your riposte! etc)
Thanks for the thoughtful reply Emily, you’ve offered some good feedback for me to consider. Here are some of my thoughts as to your concerns.
First, the concern about the reduction of options in melee combat. You are correct that the proposed amendment would effectively render Two-Weapon Fighting less effective (at least at lower skill levels), thus making it a less attractive option to use at these lower levels. This would likely have the effect of causing most players to stick with one of the other two melee fighting styles you mentioned. Of course historically this is exactly what we see in the actual world. What we have here is a conflict between the design goals of providing balanced player options and maintaining realism within the game mechanics. In this particular instance I’m in favor of privileging realism, but I understand why others would prefer to sacrifice a bit of realism to preserve balanced character options.
Second, the concern about this amendment hindering certain character archetypes more than others. I sort of touch on this in my response above but I do feel the pull of this concern. Below I’ll say a bit more about why I think the style still offers advantages to these archetypes at higher levels, but I recognize that an associated cost of implementing this amendment is a loss of balance between archetypes, at least at lower levels.
Still, at higher levels dual wielding offers the following advantages: (a) bonuses both to attack and defense; (b) the ability to make additional attacks under specified circumstances. Also I should note that in my revised rules, Rangers begin with a class feature that increases the defense bonus received for duel wielding to +2 and negates any penalties to attack. While still not as good as using a shield in the offhand (at least in my game), it’s still not bad.
Third, logistical concerns about how this attack action would work. Using the technical jargon of Pathfinder, the ‘riposte’ maneuver would essentially be an ‘immediate’ action. It would not change the initiative order and it would not affect any of the character’s actions the following turn. It would also not be an attack of opportunity. The attacking character is not performing some action that would provoke an attack, rather the PC making the decision to perform a special maneuver. Even if one goes with the first option I suggest, option a, and says that a skilled dual wielder may gain an additional attack on any combatant who fails an attack against them by 5 or more, conceptually what is happening here is that the PC has managed to parry the attack with one weapon and has the other hand free to attack before the target can return to a defensive position.
However I hadn’t considered the possibility that two duel-wielders might get into an infinite riposte loop (thanks for bringing this to my attention). To avoid a situation such as this one could specify that a PC can only attempt a ‘riposte’ maneuver once per turn, in response to an attack made by an opponent.
I doubt this will satisfy everyone, but hopefully it addresses some of the concerns you’ve raised.
I prefer your mechanical interpretation. From what little I know about historical combat, duel-wielding of weapons was almost exclusively used in dueling and fencing. I think I’ve read somewhere that Naval combatants would utilize it, because shields were a bit bulky to use on ships, but I’m not sure if that is true or not.
Either way, I do think that the point (hah) of a basic feat for two weapon fighting would be to provide a way to parry or feint and strike with the other hand. I know the famous Ronin Musashi utilized this in a sword trick that I think was called “snow falling from a willow branch”, in which he would feign a stab with a small blade, and when the opponent would strike this small blade to parry Musashi would offer no resistance with it, causing the opponent to get off balance and giving Musashi a chance to strike with the longer blade.
I do think something to think about is the romanticised view of the two-weapon fighter in melee, usually against multiple opponents, striking to and fro. While not necessarily realistic, I do think that is what many players go in for when they choose to use that type of character.
My personal take would be a set of maneuvers that accompanies each weapon or fighting style, with two-handed fighting being full of feints, parries, and trickiness. This was something that was sort of in the early fifth edition beta, but has been sadly (in my opinion) excised out or simplified as the beta has gone. My ideal would be learnable maneuvers akin to Spells for Wizards, so that Fighters or other melee types could seek out veterans and combat masters to learn new techniques. That is definitely a pipe dream, though, and probably looks a lot better on paper than in reality.
Thanks for weighing in RPC. The point you raise about the purpose of dual wielding is to be able to allow more options for parrying and feinting with one weapon while attacking with the other is exactly what I would like to capture here.
Two issues lurking in the background here are (a) how simple or complex do you prefer the rules to be, and (b) how abstract or concrete do you wish them to be. The default 3e attack and defense procedure is both simple and abstract. It is simple in that only one two die rolls are required, one for attack and one for damage (no defensive roll is required), and typically the mechanical procedure for each attack is exactly the same (though feats such as Power attack etc add slightly more complexity). It is also abstract in that the attack roll does not represent a single attack, but rather all of the attempts made to attack within a 6 second time increment. Though it should be mentioned that feat trees and fighting styles of latter supplements move the system in the direction of more concreteness.
However what your personal take of a system of maneuvers specific to different fighting styles suggests is a system that is both more complex and more concrete. It would likely more transparently model the way combat functions in the actual world. As someone who has simulationist leanings I am definitely attracted to this. However I also want my preferred game system to be relatively easy for a newcomer to learn, and to play rather quickly. This definitely cuts more in the direction of simplicity. This is why I tried to keep the amended rule as simple as possible. However, one think I am thinking of doing is creating something like a Basic and Advanced version of the revised rules, and something like fighting styles and personal maneuvers might be worth considering for the Advanced rules.