One of the best things D&D changed in recent editions is the ability to sense or detect evil in characters or non-player characters. The fifth edition rules limit the ability to sense the divine and detect evil to specific creature types such as supernatural or undead creatures. This makes a lot of sense as a demon or zombie would radiate divine power or dark magic whereas a human might not. Unfortunately, the Pathfinder rules are a bit different in this regard.
Technically, the Pathfinder spell gives the ability to detect evil in “creatures” that are at least 5 HD for 1st edition or 6 HD for 2nd edition. But does this make sense?
Should, for example, a swordsman suddenly start radiating a good or evil alignment simply because she swings her sword better? How does skill with a blade have anything to do with a person’s innate alignment or aura?
Should You Change Detect Alignment Spells for Your Campaign?
As many can attest, the ability to detect evil in PCs or NPCs can be quite limiting for a dungeon master trying to craft a story, especially if there is a paladin in the party. And because the ability doesn’t really make any realistic sense — and I know we are talking about fantasy here, but even fantasy has something called “fantastic realism” — a DM might decide to alter it to become closer to the D&D 5th edition rules.
I like taking a more literal approach to the spell. “Creatures” in this sense would be non-humanoid and non-supernatural beings such as animals, beasts, monsters, etc. Basically, detect evil would detect those beings that are evil by their very nature such as trolls rather than the rather fluid alignment in those beings that can basically choose between good and evil.
The exception to this rule would be those who have dedicated themselves to a god or goddess that is of good or evil alignment. This obviously covers priests, paladins and anti-paladins, but also any other individual who reverently worships a god.
Alignment itself is an awkward attribute in RPGs. We are rarely one thing and our motivations can be quite varied. Perhaps more important, very few people view themselves as “evil.” While they may commit evil acts, from their own perspective, they often believe they are acting for good rather than evil. Even someone that worships an evil god may believe the god is in fact ‘good’ and that the ‘good’ gods are the ones in the wrong. (And, if you look at most of our mythology, “good” gods like Zeus certainly wouldn’t be considered good by any modern standard.)
The big rule of thumb here is that a DM shouldn’t feel as if they need to follow every rule to the letter or include every spell/ability. The rules are a guideline. The DM is the master of the game itself. If you are sick of paladins ruining any attempt to introduce a complex storyline where good companions become villains and villains become the good guys, maybe its time to make some changes to those detect alignment powers.