Plane Sailing said:
The impression which I get of Florentine fighting (renaissance sword and dagger) was that although you would normally use your dagger for parrying, and indeed it often had extra stuff to help it with sword catching, a particularly good use was when you and your opponents bound your primary weapons together you had something handy to gut him with in your spare hand.
I could easily see TWF being used to give a damage bonus or an attack bonus.
Yes and no. IME, you're largely correct, but I'd like to add a few points for clarification.
By way of fuil disclosure, I trained in eastern martial arts for over a decade and have trained in renaissance martial arts (especially swordfighting) for the past 6 years. That includes, but is not limited to: single rapier/sidesword; single backsword; rapier/sidesword & dagger or buckler; backsword & buckler; quarterstaff; and italian longsword (hand-and-a-half).
The bulk of my two-handed experience is rapier/sidesword & dagger or rapier/sidesword & buckler. A typical fight goes like this after Fighter A attacks. Either:
B parries with dagger and counters with sword.
B parries with sword, deflects with dagger, and counters with sword.
B parries with sword & dagger, then counterattacks or evades.
Using a buckler is pretty similar, except that it's easier to counter-attack with a dagger than it is with a buckler.
Basically, two-weapon fighting with a light weapon (or buckler) in your offhand is mostly helpful defensively, but it can assist your offense by pulling your opponents defenses "off line." Basically, it's a way of creating a feint. It sounds to me much more like a good technique for cunning rangers and rogues than for more traditional fighters.
I would put forward the notion that a "swashbuckler" is probably closer to a fighter with rogue training (or vice versa) than to a straight fighter. Couple that with the claim that the rogue and the ranger "ganged up on the swashbuckler and split his stuff," I think we'll see two-weapon fighting as a key power for rogues and rangers.
However, fighting with two regular-sized weapons (case of rapiers, paired swords, paired hammers) is really difficult. It's clumsy and awkward. Two friends of mine with roughly equal skill were sparring. The slightly better was using case of rapiers, whereas his opponent was using rapier and dagger. By traditional standards, the former should have had the edge, but the latter one. How? His opponent got tied up trying to effectively use both blades. That means that while two-weapon fighting can be very effective, trying to use two large weapons should counteract that penalty. I wouldn't want to go up against a trained two-weapon fighter with a single blade though - even if they weren't used to the paired swords.
On the other hand, heroes can learn things that are difficult for normal people. Of course, it should probably fall into the category of powers.