[RPG] Armor as DR alternate rules: Do untyped AC bonuses apply to Defense or DR

armor-classpathfinder-1e

I'm starting a Pathfinder Campaign with the alternate rule for armor as damage reduction. I'm just wondering what gets changed to damage reduction and what stays defense. For example, a shield's AC goes into defense, but armor's AC goes into damage reduction, as does natural armor, and can be bypassed by magic. What about things that don't list a specific type of AC bonus, like mage armor? It gives you +4 bonus to armor class; does that go to defense or damage reduction?

Best Answer

The spell Mage Armor does specify the type of AC bonus:

An invisible but tangible field of force surrounds the subject of a mage armor spell, providing a +4 armor bonus to AC.

Therefore, Mage Armor adds to armor DR.

Almost everything should clearly indicate what kind of bonus it grants, which will make it clear whether it applies to Defense or to armor DR. Pathfinder aimed to fix a lot of the deficiencies that d20 had accumulated, and diligently typing every bonus that needs typing is one of the things that Pathfinder is pretty good at.

The rare exceptions of ambiguous untyped bonuses (such as when using some of the lower-quality 3rd-party d20 material in PF) can be sorted out by common sense or simply your preference. For common sense sorting: anything that absorbs the damage from a blow that has already hit you goes to armor DR; anything that prevents the blow from connecting with its target in the first place (shields being in this category) goes to Defense. If you're lucky, something that adds an ambiguous untyped bonus to AC will say whether it adds to only Touch AC or never to Touch AC, and then it clearly applies to Defense in the first case and DR in the second. Such ambiguous untyped bonuses will be the exception though – as a general rule of thumb, unless it's an armor bonus, it falls under "other modifiers" in the Defense equation.

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