Note that the rules for Two-Weapon Fighting state "If your off-hand weapon is light, the penalties are reduced by 2 each. (An unarmed strike is always considered light.)"
If an unarmed strike is a natural weapon, why is it referred to in the rules for Two-Weapon Fighting, which are not used by natural weapons?
Because in that section, you are assuming that the primary weapon is NOT a natural weapon, but a mechanical one. If you are mixing mechanical weapons with natural, and the mechanical is in the primary hand, you treat the natural weapon as light: it is an unenhanced body part- the issues of skill, balance and reach with that weapon are negated by a literal lifetime of use.
Note also that the Monk's attack penalty for Flurry of Blows (-2 for each attack in the flurry) is functionally
identical to the penalty for fighting 2 weapon style with a light off-hand weapon (-2 for primary and off-hand) except that the Monk gets more attacks.
If we have a fighter (not a monk) without a longsword, can he make iterative attacks with his unarmed strike?
Here we spot the animal known as the Raging Damifino!
Personally, I'd say that iterative unarmed strikes are limited to classes like the Monk (which explicitly can) or the Kensai (who may potentially treat his fists like all other weapons), or to any PC with a Feat that explicitly allows iterative unarmed attacks, but I don't know of anything RAW that supports it.
Look at the Magic Fang example again. The target is 'living creature touched'. Notice, no natural weapons are required to be the target of the spell.
True- but the spell still
defines a fist as a natural weapon.
+++
Additionally, I'm going to have to state that, upon reflection,
I am changing my position slightly...but not the way anyone here would think.
SINCE:
1)
Magic Fang explicitly calls the fist a natural weapon (a rule from the same book as the Monk description) and...
2) Given that the Kensai
explicitly calls the
fist of a human a natural weapon (from a book subsequent to the 3.5PHB, and thus, the more recent expression of the rules)
THEREFORE:
3) The clause that describes the Monk's unarmed attacks "both as a manufactured weapon and a natural weapon" is NOT adding the property of "natural weapon" to the Monk's unarmed attacks- the Monk's fists already ARE natural weapons as evidenced by 1 & 2 above. The clause is
instead adding the property of "manufactured weapon" to the Monk's unarmed attacks.
That the Monk can treat his unarmed attacks as manufactured weapons then becomes part of the underlying rationale for why he can make iterative attacks with his unarmed strikes, just like with his special Monk weapons.
So all that stuff I said about
only Monks and Kensai being able to take INA is wrong. The fist is a natural weapon, so anyone with fists could take INA.
The area where the Monk and Kensai twist the rules is in their ability to target their unarmed attacks with spells and effects that usually only affect normal weapons.
Here is where it matters what "spells and effects" mean: I'd argue that adding the property of "manufactured weapon" lets the Monk's unarmed strikes be the target of spells like
Magic Weapon,
Bless Weapon,
Holy Sword and other spells or effects that only affect melee (manufactured) weapons, and Feats like Cleave or Psionic Weapon.
The REAL question, then, isn't whether a Monk can take INA, but whether the Monk could have his unarmed attacks made into permanent magic weapons.
Monte Cook's Arcana Unearth addresses this directly with the feat Hands as Weapons. In D&D3.5? Yet another Raging Damifino.