AoO Question re: Readied Actions

[Cowardly Griffo]

Okay, so here's the scenario:

1. Spellcaster readies an action to cast, say, Magic Missile at an adjacent enemy as soon as they move out of the adjacent square. This could just as easily apply to an archer preparing to fire an arrow, or any other ready-able action that provokes.

2. Enemy declared they are moving away.

So what happens now? I know the readied action goes through, but my question is whether the act also triggers an Attack of Opportunity or not. The enemy has declared they are moving, but they haven't actually moved out of the square yet, and it's still their turn, so do they still get an AoO?

And if not: how deep does that rabbit hole go? What actions can someone take on their own turn and still be able to take an AoO triggered by a readied action? aside from attacking, I mean, as that seems kind of a no-brainer. Could you be drinking a potion, or doing a bardic performance?

On the one hand, it makes sense that you can't take an AoO while you're busy with (certain) other activities. On the other hand, the round structure is an abstraction and all this stuff is happening with comparative simultaneity, so it doesn't really make any more sense than not being able to take AoOs when it's not your "turn" would. And on the third hand, if readied actions don't provoke then it makes certain feats and such redundant and encourages weird headache-inducing contingent strategies.

I'd be interested to hear both what RAW says as well as people's opinions on the issue. Pathfinder or 3.5, I'm curious about both.

[Khedrac]

Since they have not moved, if the spellcaster forgot to declare a defensive cat of magic missile, then yes, the target does indeed get an Attack of Opportunity against the caster.

As for how deep the rabbit hole goes - very deep and it gets complicated, very complicated.

Generally the AoO chain goes until one of the parties has run out of attacks of opportunity to make (yes they work backwards from the initial triggering event). Effect before cause - if you only have one AoO then you cannot make another if someone provokes because you are already committed to one that is yet to happen!

Once the chain of AoOs is resolved the triggering action can happen (if still viable) and the round can continue.

It then gets worse - the chain of AoOs can leave one of the combatants unable to take the declared action (AoO or otherwise) that either triggered or formed a key link in the chain (e.g. they are dead). At this point the surviving combatants get their unused AoOs back to use alter in the round (if an opportunity arises) and, if still conscious, the character who originally triggered the cascade has to choose a different action to take.

Usually combatants are sensible enough to not attempts AoOs that will provoke, but if two Karmic Strike/Robilar's Gambit fighters square up the combat is usually not many rounds, but a lot of real time to resolve.

[ace rooster]

Quoting the SRD "The action occurs just before the action that triggers it". So if you readied it for when somebody leaves an adjecent square then they would still be in an adjecent square when you cast your spell, hence they get an AoO. That seems fairly clear.

Where it gets wierd is that I can't find a definition of when a round starts and ends. This can actually get quite important, as your AoO are dependent on it. There are 3 options.

1) The round for a character starts when they start to act.

2) The round for a character starts when they finish their actions.

3) The round starts when the initiative order goes from lowest to highest.

1 and 2 are what I find we use, and are equivilent except when a character makes an AoO in their own turn. 3 can result in characters using AoOs after they act, and then before they act in the next round, and means that a high initiative count means you will always be the first in line for AoOs.

Readied actions are not the only way this can happen, particularly if PCs are fighting someone they do not know has combat reflexes. Another situation is when characters try to grapple a character moving past as their AoO, which provokes an AoO back. Given that that AoO is the main defence against untrained grapplers it seems harsh to deny it on a character's own turn.