Lets say we have a character wearing both an armor and shield with the light fortification special ability. If this character is critically hit, are percentile dice rolled twice to negate the critical hit? I'm unsure how the stacking rule comes in to play in this case.


No, they do not stack

You'd get a single 25% chance to negate the critical; the critical section in the stacking rules text is:

In most cases, modifiers to a given check or roll stack (combine for a cumulative effect) if they come from different sources and have different types (or no type at all), but do not stack if they have the same type or come from the same source (such as the same spell cast twice in succession).

So much like any other granted ability, they will not stack as they are providing the same bonus for the same effect (critical negation) from the same source. Therefore only the highest bonus would be used.

On a mechanical note it would be much more cost effective to take two +1 items with 25% chance each (net 44% chance, 2k cost) of failing than forking out for a much more expensive +3 item (75%, 9k cost) so there's another reason to say no!

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    \$\begingroup\$ The quoted text has literally nothing to do with this case. It applies specifically to modifiers, and the effect of fortification is not a modifier. \$\endgroup\$ – starwed Jan 7 '13 at 19:33
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    \$\begingroup\$ +1 true. I'd argue that it is technically a modifier, @starwed - it's just not a numeric one. \$\endgroup\$ – LitheOhm Jan 7 '13 at 21:39
  • \$\begingroup\$ How is it "technically" a modifier, when it doesn't modify a check or die roll? \$\endgroup\$ – starwed Jan 9 '13 at 1:53
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    \$\begingroup\$ Because it's a bonus to "fortification", without this you have 0 fortification. However I can see where you're coming from. I believe that the "spirit of the rules" here for this plus things like displacement (blur 20% + displacement 50%, what happens?) are a case of "same source so the higher level effect is applied only" \$\endgroup\$ – Rob Jan 10 '13 at 14:41
  • \$\begingroup\$ @starwed: It doesn't modify a roll? It raises the chance that a critical will not happen. It just raises it from 0% so it's not normally rolled. \$\endgroup\$ – Loren Pechtel Jan 10 '13 at 20:38

No, they don't stack

In 3.5, any sort of benefit from the same source or from two sources with the same name never stacks. This is why, for example, the Monk AC bonus does not stack with the Swordsage AC bonus - despite coming from two different sources and having subtly different rules text, they're both named 'AC bonus' and as a result do not stack. You might be able to argue a RAW case for different 'weights' of Fortification stacking, but I don't think there's a DM on earth that wouldn't slap you with the book so fast it'd make a sonic boom if you tried it.

In any event, there's easier and cheaper ways to protect oneself from critical hits and sneak attacks, if such is your goal.



Fortification is not a bonus that is subject to the stacking rules - it is a magical effect and the rule here is that the most potent of overlapping magical effects prevails.

I think some confusion has come up (including in previous versions of my answer) becuase fortification is given an enhancement bonus equivalent (+1, +3 or +5 for light, moderate and heavy respecively) but this is purely for determining costs, caster level to create etc.

Another source of confusion is how enhancement bonus work with respect to armour and shields. One way of thinking of this is that enhancement bonuses enhance another type of bonus and don't apply directly themselves. So enhancement to strength do not stack but they would not interfere with enhancements to dexterity (or armour or shields etc). Magic Armour has an enhancement to its armour bonus and a magic shield has an enhancement to its shield bonus - since armour bonuses and shield bonuses are differant, the enhanced bonus of each are added to get the AC.

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    \$\begingroup\$ Uh. Enhancement bonuses are just the straight, +1, +2, etc. Fortification is a special ability that does not involve any Enhancement bonus to anything. \$\endgroup\$ – KRyan Jan 10 '13 at 5:55
  • \$\begingroup\$ To provide more detail about KRyan's statement - armor, weapon, and shield enhancement bonuses refer to the +1 to +5 that gets added to attack/damage or armor class. There are other kinds of enhancement bonuses (such as Bull's Strength), but all enhancement bonuses are a straight numeric bonus to a stat such as an ability score, damage, a skill check, or a saving throw. The terminology can get somewhat confusing, though, since weapon and armor properties are referred to as enhancements. Blame WotC for that one. \$\endgroup\$ – Lord_Gareth Jan 10 '13 at 6:25
  • \$\begingroup\$ I agree with all this, see the last sent ace that I originally left out. My point was to clarify the misconception in the other answers that if they were enhancement bonuses they would not stack; if they were they would but they aren't so they don't. \$\endgroup\$ – Dale M Jan 10 '13 at 9:34
  • \$\begingroup\$ OK, I get what you are saying, but unfortunately that's not really the question that was asked, hence our confusion. You might consider asking that actual question and answering it yourself (which you are totally allowed, and encouraged, to do); if you can clearly explain the situation and why they do stack, I'd +1 it. \$\endgroup\$ – KRyan Jan 10 '13 at 15:01

Effects like fortification do not follow the rules for bonuses stacking.

And the reason is pretty simple: they're not a bonus! The section you link to is part of a larger section on modifiers, which opens with this text:

A modifier is any bonus or penalty applying to a die roll. A positive modifier is a bonus, and a negative modifier is a penalty.

The effect of fortification does not fall into such a category. It is closer to something like concealment, which causes attacks to have a 20% miss chance. Concealment doesn't stack because the rules explicitly say so, but there's no such clause for fortification.

There are rules for combining magical effects, but annoyingly I don't think any of the specific clauses are relevant here. In any case, you could definitely argue that they apply only to spells in any case. Fortification doesn't even function like a particular spell (the enchantment is created by a limited wish or miracle) -- and warforged actually have it as an (Ex) racial trait.

Examining the rules carefully, I'm forced to conclude that yes, they do stack, simply because there are no rules saying that they don't. However, because almost all similar cases do have rules preventing stacking, you might infer that this was an oversight and not the intent.

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    \$\begingroup\$ I will have to politely disagree. Percentile dice checks are also mentioned in the "Core mechanic" section; the lead opening line to me is: "Whenever you attempt an action that has some chance of failure, you roll a twenty-sided die (d20)." However it then mentions d% as well, immediately after the d20 mechanics - therefore the implication is that a % check is also "an action that has some chance of failure" or why mention it? The stacking rule (to me) therefore applies as the stacking section rule would therefore apply to a percentile roll as well. \$\endgroup\$ – Rob Jan 8 '13 at 8:55
  • \$\begingroup\$ The wording of the section on stacking refutes that idea. Rolling percentile dice to see if something fails or not is not a modifier -- certainly not in the sense that the rules refer to. \$\endgroup\$ – starwed Jan 8 '13 at 17:56
  • \$\begingroup\$ I'm not sure why the confusion here, it's really straightforward. Maybe this thread will help clarify: paizo.com/threads/rzs2kqyj?Stacking-Fortification \$\endgroup\$ – Cypher Jan 8 '13 at 18:47
  • \$\begingroup\$ @Cypher That thread only supplies one citation for them not stacking, and it is one I specifically call out in my own analysis. FWIW, I would not be surprised if the designers had not intended them to stack, and it would be a perfectly sensible house rule, but the RAW don't actually proscribe it. \$\endgroup\$ – starwed Jan 8 '13 at 19:15
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    \$\begingroup\$ "Same Effect More than Once in Different Strengths: In cases when two or more identical spells are operating in the same area or on the same target, but at different strengths, only the one with the highest strength applies." Even if they don't imitate a specific spell, they are still a spell effect, from the exact same spell. That would be different if we were talking about "An armor of fortification and a shield of fortificatude" or whatever, but ""An armor of fortification and a shield of fortification" don't stack. \$\endgroup\$ – Cristol.GdM Jan 10 '13 at 23:27

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