Of all the aspects of a given tabletop game, one of the most debated and discussed topics is that of alignment systems. Ranging from the nine alignments of the 3.x editions of D&D, through the simplified system of 4e, to the various systems used or denounced entirely by games all around. In the end, the discussion tends to revolve not around which system is necessarily superior, but rather whether it is a good idea to have an alignment system present in the game at all. While I will hold throughout this series that these systems are beneficial to the game, the introduction to this discussion hinges on the point that there are really only two approaches to alignment in general that handle the issue in a satisfactory manner.
If a game is run and plans to integrate a lot of alignment-based abilities (Smite Evil, DR /alignment, etc.), I think this quote sums things up best:
A character debating the morality of their actions in the actual game is a perfectly wonderful thing, but when it comes to debating the system itself at the table, there is a problem. This is why an objective system of alignment is the only suitable one for a tabletop setting.
When alignment-based abilities are involved, sticking to a system’s definitions is crucial. I can argue all day about why my evil-aligned character believes the ends-justify-the-means and hopes to one day make a better world, because that just makes a well-developed and realized character. The character’s opinion of their alignment isn’t terribly relevant if the system declares Smite Evil has an effect, though. Besides, imagine the internal conflict that ensues when the character who thought he was following a good cause is smited by an obvious Avatar of Good.
Having an objective Good/Evil system makes the abilities actually possible, but it puts in some interesting roleplaying concepts. A person could, by use of a few spells (or magic items) look at their own alignment. Imagine one day looking down and realizing you were no longer Good, like you used to be, and you couldn’t recall when it had happened.