I think consulting the rules here is relevant.
to make more than 1 attack in a round requires the full attack action. If you are using two weapon fighting to do this, you must state so, because you take a penalty on your attack roll with both primary and secondsry weapons (the penalty varies depending on feats and weapons used).
Your statement of intent must therefore involve the fact that you intend to use two weapon fighting. There is no way around this. (You could abort and use a move action later if needed)
Under the rules for two weapon fighting it states "If you wield a second weapon in your off hand, you can get one extra attack per round with that weapon."
It is clear that your extra attack comes with the second weapon, and that must be the weapon being wielded in your off hand.
It's clear that you must be wielding two weapons in order to perform two weapon fighting.
It is clear that the weapon in your primaty hand is the first weapon
It is clear that the weapon in your off hand is the secondary weapon.
It is clear that the first and second weapons are different weapon.
From those it should be blindingly obvious that you cannot swap one weapon from your primary to your off hand and then attack with it, as this is the first weapon, and the extra attack comes from the second weapon.
It is clear that at the time you begin to use two weapon fighting (doing a full attack) you must have two weapons in hand. Otherwise it would not be legal to perform two weapon fighting (because of the penalties).
I maintain that the weapon you make the offhand attack with must be the same as the one you began with. Because of the penalties.
Hypersmurf's complicated example of attack, step, drop, draw, attack fails, because the new weapon drawn may impose different penalties on the attack roll that you have already resolved and therefor a different result.
1st attack (longsword vs zombie AC10). Assume rolls 11, -2 (2 weapon fighting) +2 from BAB/Strength). that's a nett 11 vs AC 10, a hit. damage kills zombie.
5' step to skelly, drop handaxe, draw a heavy mace and attack skelly with that.
At this point looking backwards we see that the 1st attack should have taken a additional -2 (from non-light in offhand) which would have resulted in the 1st attack missing. This would result in a violation of the underlying space time continium and so cannot be allowed.
Therefor to keep the rules consistant and prevent this sort of thing happening, and from all my previously earlier conclusiongs I would state the following
To use two weapon fighting in a round you must begin your attack sequence with the two weapons you intent to use throughout the full sequence of your attacks.
to make more than 1 attack in a round requires the full attack action. If you are using two weapon fighting to do this, you must state so, because you take a penalty on your attack roll with both primary and secondsry weapons (the penalty varies depending on feats and weapons used).
Your statement of intent must therefore involve the fact that you intend to use two weapon fighting. There is no way around this. (You could abort and use a move action later if needed)
Under the rules for two weapon fighting it states "If you wield a second weapon in your off hand, you can get one extra attack per round with that weapon."
It is clear that your extra attack comes with the second weapon, and that must be the weapon being wielded in your off hand.
It's clear that you must be wielding two weapons in order to perform two weapon fighting.
It is clear that the weapon in your primaty hand is the first weapon
It is clear that the weapon in your off hand is the secondary weapon.
It is clear that the first and second weapons are different weapon.
From those it should be blindingly obvious that you cannot swap one weapon from your primary to your off hand and then attack with it, as this is the first weapon, and the extra attack comes from the second weapon.
It is clear that at the time you begin to use two weapon fighting (doing a full attack) you must have two weapons in hand. Otherwise it would not be legal to perform two weapon fighting (because of the penalties).
I maintain that the weapon you make the offhand attack with must be the same as the one you began with. Because of the penalties.
Hypersmurf's complicated example of attack, step, drop, draw, attack fails, because the new weapon drawn may impose different penalties on the attack roll that you have already resolved and therefor a different result.
1st attack (longsword vs zombie AC10). Assume rolls 11, -2 (2 weapon fighting) +2 from BAB/Strength). that's a nett 11 vs AC 10, a hit. damage kills zombie.
5' step to skelly, drop handaxe, draw a heavy mace and attack skelly with that.
At this point looking backwards we see that the 1st attack should have taken a additional -2 (from non-light in offhand) which would have resulted in the 1st attack missing. This would result in a violation of the underlying space time continium and so cannot be allowed.
Therefor to keep the rules consistant and prevent this sort of thing happening, and from all my previously earlier conclusiongs I would state the following
To use two weapon fighting in a round you must begin your attack sequence with the two weapons you intent to use throughout the full sequence of your attacks.