Assume alignment has a good-evil or a law-chaos axis and further assume that the rules system uses some sort of reaction rolls, with a good result meaning (more) favourable reaction and a bad result meaning hostile or negative reaction.
If using a law-chaos axis, then any lawful character has their reaction improved by one step if they assume the other party is lawful, and worsened by one step if they assume the other party to be chaotic.
If using a good-evil axis, then the reaction of good character to everyone increases by one step, while the reaction of evil characters to everyone worsens by one step.
A good society is a nice place. An evil one is not. But any good character might be taken advantage of and might not do as well as an evil character, especially in a situation of scarcity. This is a sort of prisoner’s dilemma. Law and chaos are mere tribes.
To determine the alignment of an established player character (that has been played for a while), consider:
- How do they treat characters they assume to be lawful when compared to those they assume to be chaotic? If they clearly favour one side, then that’s their chaos-law alignment.
- How do they treat complete strangers? If they mistreat them, they are evil. If they treat the strangers with caution, they are neutral. If they try to help and aid strangers, treating them as friends, they are good.