skeptic said:
In fact it's the opposite : your alignment reflects your behavior ! If your behavior changes over a certain time, your alignment changes to represent it.
Well, there are arguments both ways.
Let's take the example of Xena, the evil warlord, who slaughtered the innocent and enslaved thousands as she and her armies marauded across the land.
And then Hercules defeats her but spares her life, and she has an epiphany, and decides to devote her life to goodness and protecting others and all that neat stuff.
At this point, what is her alignment?
Some people would say Evil; alignment is effectively a record of past deeds, and Xena has not performed any good deeds to balance the evil of her past.
Some people would say Good; alignment reflects someone's outlook and state of mind, and illustrates how they might react to a given situation. After her epiphany, Xena will react in the same way that any other champion of goodness would; her state of mind is Good, and so therefore is her alignment.
Some people would say Neutral; she has turned away from darkness (and is therefore no longer Evil), but Goodness is something that must be earned with deeds.
Evidence in favour of the 'record of deeds' interpretation:
The wearer of a phylactery of faithfulness is aware of any action or item that could adversely affect his alignment...
The implication is that an action could alter someone's alignment.
Evidence in favour of the 'outlook' interpretation:
On a failed save, the alignment of the wearer is radically altered to an alignment as different as possible from the former alignment—good to evil, chaotic to lawful, neutral to some extreme commitment (LE, LG, CE, or CG). Alteration in alignment is mental as well as moral, and the individual changed by the magic thoroughly enjoys his new outlook.
The victim of the Helm of Opposite Alignment takes on the outlook of the new alignment. Under the 'record of past deeds' interpretation, an alignment has no outlook; it is merely a log of current position based on actions.
I personally favour the outlook interpretation; once Xena has her epiphany, her alignment is Good, even before she has begun acting on her new resolution.
-Hyp.