Alignment as I described it in my last post is a single axis: Law-Chaos. Good and Evil are part of this axis, instead of a separate axis; the New School conception of alignment as personality traits is not applicable. Staid traditionalist characters and free-spirited characters (the New School interpretations of Lawful and Chaotic) may support either Law or Chaos.
Most individuals, however, no matter what their personality type, will fall into the category of Neutral, neither particularly helping nor harming the cause of either Law or Chaos; in fact, most everyone is ignorant of the struggle, not taking it seriously on the few occasions when they do hear about it.
In fact, until they begin to establish themselves and discover the reality of both the forces of Law and Chaos, the PCs won't usually know about it. That's what sets Paladins, Rangers and the more devout Clerics apart from your average Fighters, Thieves, Magic-Users, most Clerics and all the other classes: they're true believers from the beginning in a grand cosmic struggle, instead of stumbling upon it in the course of amassing their personal fortune. It's why Paladins and Rangers exist, and why Clerics are sent out to fight Chaos instead of blessing crops and healing the sick on a full-time basis.
So, how to deal with alignment when the PCs don't even know about or believe in it? Well, I could just let the players decide their PCs' alignments, but that, I think, risks making this more about what color jerseys the PCs are wearing instead of which side they're actually scoring for. It also bares for my players a part of the setting that I really don't want to just tell them about. I want them to discover it along with their PCs.
It's true; I've begun keeping secrets from my players. They don't read my blog and they have no idea that Dragons run much of the world. They're just starting to get an inkling of the Cthuloid horrors continued adventuring will bring them in contact with. I think I may have mentioned the possibility of Mindflayers and they've fought a Shroom, like, once. They have no idea that Necromancy exists in my setting at all. They certainly don't realize that Carcosan rituals exist and are utilized by evil sorcerers, nor do they know why intelligent monsters have tried to kill them twice (after rolls on the Puppet-Master Machination Tables), although they are getting curious about that.
To be clear, when there have been questions about these things, I haven't refused to answer. Instead, I told my player that there were good, non-arbitrary reasons for what was happening; cause-and-effect was occurring. I told him that I thought it would be more fun for him to figure out what was going on through the course of play, but that I'd be willing to explain it to him if he preferred that. He opted to try to figure it out, at least for now.
My gut tells me to do the same thing with alignment. Tell most players not to worry about it. Slip the players of Paladins, Rangers and Clerics of certain gods secret handouts about their characters' understandings of Law and Chaos. Then come up with a scale for measuring alignment and a list of Lawful and Chaotic actions: actions which materially benefit Law or Chaos. Different classes may start out on different points along the scale (Paladins, etc., start out high on the Lawful scale, while most other classes start out near halfway or so. Thieves start closer to Chaos but still inside Neutral territory.) and I adjust their scores as they perform action on the lists in the course of their normal adventuring career. This idea, by the way, is stolen almost whole-cloth from the Judges Guild Ready Ref Sheets; the differences are that the Ready Ref sheets try to work with a double-axis alignment system, that there is no list of Lawful or Chaotic acts and that you're supposed to roll for your alignment.
Next time I'll try to flesh this out mechanically. In the meantime, how much about your settings do you keep away from your players, waiting to reveal through play? Is most everything pretty straightforward or are there definite twists that make your players sit up and take notice?