Your first attack happens, at your full attack bonus including all modifiers. Then, if you are using the "Full Attack" action you subtract five from your 'base' attack bonus and if your base attack bonus is still one or more then you make another attack with the now reduced base attack bonus. You then do the same thing with the reduced base attack bonus.
With a +6 attack(A) modifier:
BAB|#As|A progression
1 |1 |+7
2 |1 |+8
3 |1 |+9
4 |1 |+10
5 |1 |+11
6 |2 |+12 +7
10 |2 |+16 +11
11 |3 |+17 +12 +7
16 |4 |+22 +17 +12 +7
There may be an unwritten rule that means that nobody gets more than 4 attacks from base attack bonus alone, but as stated, it is unwritten. There is an epic rule that states that you stop accruing base attack bonus when you become an epic-level character(Effective Character Level 20+) but a mature adult gold dragon(C.R. 19) has a base attack bonus of 26 and is perfectly capable of polymorphing into a form which uses a weapon, at which point the D.M. has to either grant it 5 attacks from progression, treat it according to epic rules(which would reduce its attack bonus by 3), or fudge something...
It could be interpreted that the force damage from a weapon doesn't affect an incorporeal opponent unless the weapon actually hits them. The alternative creates all sorts of headaches if an incorporeal creature tries to wield a weapon with force damage. Can they hold the handle? Can they throw it by the blade? Would that cause damage to them? But I really wouldn't know what the rules say on the matter. But force is almost unresistable, while a single second-level spell can render someone immune to 1d6 electric damage for a whole combat...