Tavish-- your proposal is undesirable for exactly the same reason attack stats are: enforced specialization with the option to suck.
Frank -- there is at least one case in which specializing defenses is desirable, which is when the deadliness is set way the hell up.
If there are a large number of effects in the game that disable a character for the length of one fight, and fights take a small amount of real time to resolve, you could conceivably make challenges so deadly that nonspecialized characters are blown away.
Imagine a mindflayer's mind control is so deadly that you can't meaningfully fight them *unless* you specialize in Will, then you want your party to have a Will specialist. And the Will specialist doesn't mind losing super hard against the Dragon, because *everyone* except the fortitude specialist gets owned quickly.
I don't think this is a terribly desirable model, but thought I would point it out.
Attributes
Moderator: Moderators
Tavish's system could be made (somewhat more) workable, if attributes applied only to defenses; if your Red defense is equal to the number of Red attacks that you know, and your Blue defense is equal to the number of Blue attacks that you know, then, at the very least, you have a reason why you might specialize your defenses.
Of course, this could have the opposite effect and make people just generalize their defenses. That might be more likely.
There are two ways to encourage (not require) defense specialization: Attack Stats of some kind, and Attack Control.
For the former, Sideways is better than forwards; if you hand out RNG abilities that make your attack work better, you overspecialize. If you give self-support abilities and added-effects on attacks, such as minor knockback and so on, then you might encourage a proper degree of specialization. If you make it so that, for instance, your Intelligence allows you a limited per-day number of rerolls on your attack roll, or your Strength adds a knockback to your attacks, for instance, or even if, to recover an ability, you roll an attack at a fixed bonus against one of your defenses associated with the ability and get it back if the attack misses, then you haven't broken the RNG, don't necessarily require overspecialization (especially if multiple attributes affect the same attack in different ways).
For the latter, the PCs need a way to force the monster to fight their way. If a PC starts a swordfight with a monster, the monster should have to sword (or claw, or spear, or whatever) fight back, against the PC's sword defense; moving the battle to one where the monster can use the PC's magic defense should cost the monster something; a PC psychic invading a monster's mind prevents/impedes the monster from fighting back in other ways; it must fight the PC psychically.
Of course, what's sauce for the goose is sauce for the gander; the monsters will likewise attempt to engage the wizard in swordfights and psychically invade the fighter's mind; the PCs might have teamwork abilities that allow a character to swap places with someone fighting along a bad defense; the swordfighter jumps into the melee so that the wizard can get back, and the psychic enters the swordsman's mind to pull the illithid out.
This encourages defensive specialization by making monsters have to target their attacks where they will be least effective, because the PCs make anything else impossible/cost extra actions. Under this system, the defensive generalist becomes the stopgap character who fights something while waiting for the specialist to step in.
Finally, of course, you can just make weaknesses mandatory.
Of course, this could have the opposite effect and make people just generalize their defenses. That might be more likely.
There are two ways to encourage (not require) defense specialization: Attack Stats of some kind, and Attack Control.
For the former, Sideways is better than forwards; if you hand out RNG abilities that make your attack work better, you overspecialize. If you give self-support abilities and added-effects on attacks, such as minor knockback and so on, then you might encourage a proper degree of specialization. If you make it so that, for instance, your Intelligence allows you a limited per-day number of rerolls on your attack roll, or your Strength adds a knockback to your attacks, for instance, or even if, to recover an ability, you roll an attack at a fixed bonus against one of your defenses associated with the ability and get it back if the attack misses, then you haven't broken the RNG, don't necessarily require overspecialization (especially if multiple attributes affect the same attack in different ways).
For the latter, the PCs need a way to force the monster to fight their way. If a PC starts a swordfight with a monster, the monster should have to sword (or claw, or spear, or whatever) fight back, against the PC's sword defense; moving the battle to one where the monster can use the PC's magic defense should cost the monster something; a PC psychic invading a monster's mind prevents/impedes the monster from fighting back in other ways; it must fight the PC psychically.
Of course, what's sauce for the goose is sauce for the gander; the monsters will likewise attempt to engage the wizard in swordfights and psychically invade the fighter's mind; the PCs might have teamwork abilities that allow a character to swap places with someone fighting along a bad defense; the swordfighter jumps into the melee so that the wizard can get back, and the psychic enters the swordsman's mind to pull the illithid out.
This encourages defensive specialization by making monsters have to target their attacks where they will be least effective, because the PCs make anything else impossible/cost extra actions. Under this system, the defensive generalist becomes the stopgap character who fights something while waiting for the specialist to step in.
Finally, of course, you can just make weaknesses mandatory.