I was watching episode 5 of Knights of Everflame, and heard Jason Bulmahn mention that good damage and positive damage were two different damage types. I see the reason for a distinction between a Disrupting rune and a Holy rune, for example, that would be supported by this distinction.
The weird consequence of this, though, is that it seems like a cleric or champion channeling divine power to use a heal spell or other positive healing energy to harm an undead would have the positive trait, but not the good trait. This makes sense that it's not automatic, but the complete absence also seems strange. For example, it makes some sense that the heal spell from a cleric of Pharasma wouldn't have the good trait, but the heal spell from Sarenrae would seem like it would have the good trait.
Even if you use the Holy Castigation feat so that your heal spell can damage fiends as if they were undead, the spell is still just a positive spell, not necessarily a good spell. It seems odd that holy water deals good damage, but the direct divine power that gives holy water its power doesn't. (This also raises the tangential question: Can a neutral priest of Pharasma create holy water, if neither they nor their deity are good-aligned?)
Am I reading this right? Or do divine spells cast from a good deity gain the good descriptor as well as the positive descriptor (and maybe I'm missing the reference)?
I agree that it's a little weird Holy Castigation doesn't include good damage. I assume it's because basically every fiend has good weakness, and that would be too powerful for a level 1 feat. Maybe another feat with that as a prereq can be home brewed to optionally change the damage to good.
In D&D onward, the Positive/Negative & Good/Evil dualities have mirrored each other enough that the distinction is blurry.
So yes, there is that Cleric feat, Holy Castigation, which requires you to be good and it makes Heals holy (according to the feat), but it doesn't do any Good damage.
Unless afterward via Castigating Weapon, where the residue energy adds Good damage to your attacks.
Both only damage fiends, so I guess the energy is caught between little good and big Good. Ya' know, holy, an even blurrier term (though I don't think it's technically a game term, so much as a common flavor).
One way to look at this is Positive Energy describes the life/health force & essence, while Good is a spiritual force & essence.
The Western body & mind dichotomy/dualism/"problem" reflected in RPG paradigms. (Though there's also Eastern Ki (chi), which in the Monk's Disrupt Ki feat is called the inner life force. If blocked, the target takes negative energy. And Ki can be linked to elements & force effects too so it's perhaps more complicated. Maybe the energy of the universe/creation?)
Or take the demon Lamashtu, a matronly figure who encourages fecundity & growth. She can give Heal Channels to her Clerics, despite being monstrously evil. She's also a chaotic masochist with the Family domain, which has Soothing Words & Unity. She needs therapy.
It also gets weird with Undead. How about those that arise from pure evil, negative energy incarnate? They're practically Outsiders and arguments have been made to label them such. (Un-dead does imply having survived being dead.) PF1 (James Jacobs) had a major push to cleanse undead of all their neutrality and even occasional honorable goodness as found in various 3.x settings. Some has crept back in, like in Reign of Winter.
Essentially (no pun intended), the flavor, contrasts, & distinctions all shift to suit whatever the story, setting, & characters require.
I think Paizo wanted some fiend-busting Clerics so they gave them two feats to equip them for such battles, using the class's main pool of power/shtick as the resource.
Oh, and then there's Occult and magic linked to ancestral worship which are both about spirits too..