How does the abstraction of AC make sense when flat-footed?

Question

I am looking for a rule-wise explanation of the logic as to why your deflection bonus (e.g. a shield) is counted in your flat-footed AC.

From what I understand, being flat-footed means you didn't see the attack coming, and are unable to react to it, so only your passive armor counts (meaning the opponent still has to hit 'hard enough' to actually pierce your protections). In that context, how would you be able to parry? You can't dodge, you should not be able to parry as well. I realize a shield can be useful if you can't dodge because you 'just have to raise it'; The problem is not every flat-footed situation should allow for a shield to be used.

Pushing things to the extreme: consider an invisible character sneaking to a guard. The combat is not started, the guard is unaware of any danger. The character is behind the guard, unseen, unheard, and ready to hit. Why would that guard's shield be taken into accout? Why would his armor even be? The character should be able to stick its dagger in the guard's neck (or any other not-armor-covered part) and deal a good amout of damage without having much armor to go through.
If I'm not mistaken, according to the rules that guard should be flat-footed. This means if the character attacks the guard, the rules consider he is able to: sense the attack, turn around, deflect the attack with his shield.

From the logic of that context, I'd say that guard should be considered defenseless, shouldn't he?

My table had trouble with a player recently contesting the logic of that rule (and honestly I can't blame him), and we had trouble making him accept that yes, his paladin's shield was useful against that ogre's enormous club.

Answer 1

First, shields don’t give deflection bonuses. They give shield bonuses. The difference is not so important for discussing flat-footed targets, but touch attacks ignore shield bonuses (and don’t ignore deflection bonuses), so the difference is pretty important when someone is trying to touch someone else.

Second, abstraction is a major part of the game. Both shields themselves and the flat-footed status are heavily abstracted, and cover myriad different things with singular mechanics. Abstraction is necessary for any game, to simplify the rules and keep the game moving, but by definition they must come at the loss of verisimilitude. By covering many different things with one rule, you accept that some of those things don’t really quite “fit” the rule precisely.

So, for shields: there is no concept of “active” shields and “passive” shields, so a giant tower shield, which is effectively a wall that you carry around, grants the same type of bonus as a simple light wooden shield. Also, note that the “buckler” appears to be used more like what the real world called a “targe,” strapped to the arm, rather than actively in the hand as true bucklers were. True bucklers do not appear in the game.

And flat-footed or losing Dexterity to AC (which are separate things!) covers lots of different situations:

• Being attacked by those you cannot or do not perceive, such as invisible opponents or being caught by surprise.

• Being distracted by other things, for example when you are climbing or balancing on something.

• The result of various effects, such as being stunned.

Note that these are all very different, but use pretty unified mechanics (some are flat-footed and some just lose Dex to AC, but since we are talking about AC and ignoring uncanny dodge, I’m ignoring that distinction here since it doesn’t really come into play).

So someone with a shield and flat-footed might have their arms completely limp at their side, and the shield just dangling.

Or they could be holding up a huge wall, just not really certain where an attack is coming from.

Both of these situations use exact same mechanics. As such, keeping the shield bonus to AC is a compromise—chosen to keep the game simple and to make shields a little more valuable than they otherwise would be. In the first case where the shield bonus maybe shouldn’t really be in play, the bonus is small, but losing the large, expensive bonus of a tower shield in the latter situation is just wrong. So getting the latter situation right was favored here.

Answer 2

I'll address a few issues separately.

Deflection bonusses

Shields don't give these. They count to your AC while flat-footed because they are generated by magical effects and serve as a sort of always-on defensive barrier around your character. When someone swings a sword at you, your Deflection bonus is a magical force trying to push the sword away, with no action required by the wielder.

Attacking an un-aware guard while invisible

You make it sound much simpler than it is. The guard might be unaware of you, but he is not a statue and you are not inaudible. That means what you're trying to do is stab him in the tiny joint between the helmet and the breastplate, without making a noise or even so much as breathing on him. And he'll be occasionally moving around, coughing, talking, and other such things that make you likely to miss.

Obviously, if you succeed, you'll deal a lot of damage. If you fail, you deal none, because you're not swinging hard enough to dent his armor. The better his armor, the better you need to aim to stab him in the exposed area.

This is modeled simply by counting his Armor towards AC, because better armor will have less exposed area to stab him in and even if he is not aware of you, that will still mean aiming more.

Using your shield while flat-footed

This is two sided. If you know you are in combat and have your shield out, it will count towards your AC even if you are flat-footed. This is because even if you cannot actively parry, shields are big and you will intuitively use them to cover your weak spots. This simply leaves less area for an opponent to attack, which makes it harder for them to land a hit.

On the other hand, if you are not aware that you are in a combat, it is very likely that you aren't actually wielding your shield. It takes a Move-action to Don a shield. If you haven't done that, it's bonus does not count to your AC. While you are just walking around, you probably haven't actually donned it and you won't benefit from its bonus.

But what about stabbing someone flat-footed in the back?

Pathfinder by default does not have facing rules, which means there is no such thing as "in the back". If you have facing house-rules, it seems perfectly reasonable that your shield does not count if you get attacked in the back.

And how does my shield work against Ogres?

Realistically speaking, a 600 pound, 9 foot Ogre will maul you to death despite all your armor and shield. Then again, realistically speaking, the Ogre would probably not be physically possible any way. I guess here we have to say "Well, if we can accept dragons and magic and giants and other crazy things, we can also accept that in this world a hero can block a blow from one with his shield."

Otherwise, a lot of standard fantasy tropes wouldn't work and that's ultimately what the game is built on.