expand_less Characters have two alignments in Ledge Campaigns: public and private.  You public alignment is akin to your reputation - it's a reflection of how others judge you by your actions.  Your private alignment is tied to your character's beliefs - why do they choose to take action?  Your public alignment is known to other players and NPCs, while your private alignment should be kept between you and the GM.  Over the course of the game, your public alignment will change in response to your character's actions (and how those actions are perceived), but your private alignment will only change in response to character development (when you've had a change of heart).  It may be possible that your character doesn't even know his or her private alignment, but as a player you should.
Functionally, either alignment may be used to qualify for rules or options that depend on alignment.  When it's your choice, you can decide which alignment applies in that case.  When it's not your choice (such as when a Paladin smites you), they choose whether or not to apply your public or private alignment.  Vigilantes and other characters that can create new personas can choose to gain an additional public or private alignment when they do so.
For example, if your public alignment is Lawful Good but your private alignment is Lawful Evil, you can still gain levels as a Paladin.  If your public alignment ever changes, however, you'll become an Ex-Paladin.  If you secretly cast an evil spell, you could not fall, as you can count your alignment (and any codes of conduct dependent on alignment) as though you were evil.  The reverse could also be true: a tyrant could cast evil spells while continuing to progress as a Paladin so long as her beliefs were consistent with a Lawful Good alignment.  At some point, she will have to come to terms with her actions, however.
Only characters that have both a good public and private alignment can be exalted (and take exalted options).  Similarly, only publicly and privately evil characters can take vile options.
Players should expect that their public alignment will change frequently,frequently (as determined by the GM), but that their private alignment won't change without their consent.