Combat Expertise
Celebrim
Legend
Errr, "Yes" and "No" depending on what you mean by that. Technically, you need be in combat to use Combat Expertise although the definition of 'in combat' is something people argue over. Officially, Combat Expertise replaces the Fighting Defensively stance, and as such only occurs as part of the declaration of an action. I suppose there is no reason to enforce that any particular attack has to happen to use it, but an action declaration certainly does.
If you just wish to improve AC you could take the 'Total Defense' action, though keep in mind that normally when in the Total Defense stance you lose your threat zone and are therefore ineligible for attacks of oppurtunity, that Total Defense is a full round action so you won't be moving very fast, and that technically Total Defense is also an action in combat.
Not also that regardless of whether you are allowed to creep down a corridor in a defensive stance, the bonus to your AC for Combat Expertise, Fighting defensively and so forth is a Dodge bonus and so does not apply any time you are flatfooted with respect to an attack or denied your dexterity bonus. Thus, it won't do you any good against a trap or an attacker you haven't observed, until you get a chance to act with knowledge of the attacker - at which point you by definition must declare the stance to benefit from it. So in general, it's a rare circumstance that declaration of the stance would help you anyway except perhaps in an armed parlay.
Suppose I'm talking to my enemy. He's in front of me, I don't want attack him but I suppose he will do instead within few rounds...
If I lose initiative, having Combat Expertise +5 (without mention Improved Combat Expertise) is better than Total Defense.
Celebrim
Legend
This is precisely the case that I mention causes arguments.
In my opinion, you are in combat and can declare whatever wary sort of stance you like - even if initiative rolls haven't been made.
In the opinion of other DMs, the fact that you haven't thrown initiative means that you aren't in combat and can't declare actions that are in combat.
My counter is that as soon as you became aware of the enemy, and the enemy didn't immediately attack, the oppurtunity for surprise has been lost. Both parties are now effectively in combat - though both sides are basically declaring things like 'delay initiative' and 'hold action' while they engage in the important business of talking - and so long as both sides are wary and observing the other, neither side can get a jump on the other. Basically IMO your character and the enemy both rolled initiative some rounds ago, then both declared the intention to parley, and you are declaring something like, "I'm holding an attack defensively standard action, with the trigger of hostilities errupt and an enemy enters my threat zone, each round while negotiations continue or until I declare otherwise."
I've got no problem with that, though some DMs are much more anxious about getting their surprise round in and would make a big stink about that sort of ruling. In fact, some DMs are so testy about getting their surprise rounds in that they refuse to even let the players ask for an initiative check and combat resolution unless the players declare an attack action - basically forcing players to be sacrifices for their inevitable sudden betrayal as if that was cool or something. Blegh.
I will note that I'd interpret as a implied condition of this action, that you are basically standing their with your sword pointed at the enemy unless you have Quickdraw or similar ability. Otherwise, you are only holding the, "I draw my sword action." Being in a threatening stance like that could influence how the parlay proceeds for good or bad.
