Currently writting a campaign set in a post apocaliptic type setting. A single last city surrounded by uninhabitable chaos sort of affair. I want there to be to be no gods, they too were victims of the war that destroyed the rest of the world, but I still want clerics.

At the moment I'm thinking that clerics would get their 'powers' from their domain, life, nature, war etc. directly, which they serve. If they go against that domain concept they can loose ability as if they have erred from their god in more typical play.

But I have a quandry, the clerics believe the domain concepts are 'real' things that give them their divine magic, whilst the wizard scholars of the city think it comes from either their own belief, or that of the people as a whole, in that domain/concept. I haven't decided if either interpretation is right or if I even need to make that descion and should leave it a a complete mystery.

I wondered if people had thoughts on what interpretation or leaving it unresovled would be more interesting? Also if anyone has done anything similar in their games and how it worked out.

A nihilistic cleric sounds difficult, but doable. Being the DM however, you have final say on those sort of domains. If it were me, I would frame it as a cleric who uncovered some lost knowledge that spoke of divine beings existing on other planes. This is similar to the Dark Sun campaign where Clerics get their powers from elementals and the planes they inhabit. Elementals aren't celestial, but one could argue their pure elemental power is similar to a celestial's power. 

You could have the Clerics be people who were exposed to the shards of the dead gods, bestowing them magic related to the domains, but without the guiding hand of a living deity to give them instructions.  If you want, this could create a new religion sort of like the Highlander, where "there can be only one" and these individuals with divine power have to keep an eye out for others who might be seeking to kill them.

in a post apocalyptic scenario with dead gods, maybe it's less about domains or circles or whatever and more about tapping into the shared situation. clerics of boundless hope, of senseless suffering, of order at all cost, of hunger for flesh, of refuting the old ways, etc. each might rally around very human saints who embody that very emotionally charged platform. saint temperance feeding the dock ward. the saint of nails going around nailing the hands of scholars to their history books in warning. players likely wouldn't be saints but they could be great complicated leaders to encounter.

even more, there's great incentive there for clerics to travel and spread the word to empower their side's message. a cleric of refuting the old ways might seek out and break magic items, encouraging others to do the same. a cleric of boundless hope might plant fruit tree saplings at every minor oasis they encounter but never claim credit. bandits might rally around one evil cleric of senseless suffering while a good-aligned cleric of senseless suffering liberates slaves and the oppressed. the room for differences in interpretation even among the 'faithful' and their drive to do more for the cause sounds pretty interesting to me. i really enjoy a character with a sense of purpose outside of 'keep friends topped off.'

Cheers, for the thoughts.

Its kind of central to  my concept that there really is almost nothing left of reality including other planes even, so no 'outside infuences' like elementals or other beings from other planes. The 'shards of dead gods' got me thinking, maybe clerics are getting their 'powers' from the last echo's of the gods.

Or maybe I need to bite the bullet and have no divine magic, but that seems to rule out a lot of player choice in character creation and then there's the healing issue.

I have always used the mechanic that the gods are manifestations of belief.  And that manifestation can create miracles aka divine magic.  As such even if there are no 'gods', there are still those with faith and commitments.  These oaths and beliefs can actually create a new 'god' to power their magic, creating a bit of a chicken/egg loop.  And that also creates a sense of mystery to it all that leaves wizards going "how does this work?!?" to which the cleric just says "gotta have faith".

Why can't everyone do that?  Because TRUE faith is a rare gift that often is hard to find in those who dedicate a life to the belief that logic is superior.

Quote from AnealeDBruin >>

Cheers, for the thoughts.

Its kind of central to  my concept that there really is almost nothing left of reality including other planes even, so no 'outside infuences' like elementals or other beings from other planes. The 'shards of dead gods' got me thinking, maybe clerics are getting their 'powers' from the last echo's of the gods.

Or maybe I need to bite the bullet and have no divine magic, but that seems to rule out a lot of player choice in character creation and then there's the healing issue.

that's the direction i was kinda leaning. the surviving priests and lay leaders are powerless and so others have stood up. named 'saints' by others, they aren't tapping into some other plane but rather you might say they're just getting famous for their actions. actions which, in a time after so much upheaval, may begin to sound mythical in their retelling. here's where you could stop for sure. however, i took it a step further by suggesting that humanity's need to believe in something shifted the light/mantle/burden of faith onto these central figures whether they wanted or not. and from that some of their followers, whether or not the saints would teach them or even claim them, have found the power to perform miracles of their own. what would those jaded, fallen, abandoned priests think of that?

alternatively, i really dig your idea of simply no clerical magic. that still potentially leaves you with paladins whose oaths, many will argue, aren't divine at all (i'm up in the air about it). maybe druids, pulling from nature as ever, are a big thing now or maybe they're disconnected as well and becoming strong herbalists to compensate. dark sun was mentioned where the wizardly magic was essentially outlawed for draining (and defiling!) life around the spell. sounds like a solid system to poach from for a sort of "life... finds a way" message: when there's no more magic, humanity scrapes out a different kind of magic. maybe this leads to a market for improvised magic with artificers searching out ruins and old magic to drain for their infusions. something to really give heft and value to the lowly arcane check. or, ghosts and ancestors lending more of a hand now that no god is stuffing them back into their infinite elysium fields of rest. oooh, yeah, what's up with hell now that there's no gate keeper?

A cleric doesn't necessarily need a god, they draw their power specifically from faith, just like how a palladin doesn't draw power from a god necessarily, but from the strength of their conviction towards their oath. A cleric can have faith in a god, or faith in what a god represents, OR a cleric can draw power from their faith in The Truth, or their faith in The Revolution, or their faith in the Natural Order of Things, any number of concepts that can coalesce into a tenant of faith.

i's going to give a character that can serve as an example  of what I'd do: 

the silent saint 

they say he saw the great apocalypse and so he swore an oath to remember each soul that died that day. so he blinded and deafened himself as well as cutting out his own tongue to remove all distractions, he now wanders the wastes carving the names of the dead he finds on his great stone tablets many of been inspired by his deeds and thus imitate him travelling gathering the names of the dead to remember them in the hope that the dead are never forgotten 

again just my opinion you can disregard this if you want 

Maybe clerics get their power from the philosophy they follow. Other possibilities could be like the cleric could do something like swear an oath to protect avenge or something else, similar to paladin or something else like that. Even if it’s just like the cleric gets their powers from their general personality kinda like FCG.

Is Divine Magic different from Arcane Magic?

the domains are "concepts" -- and some of them presume that the domain has sentience, awareness. 

One option is that each cleric doesn't take a domain, they take three to five special abilities from different domains.

Another is you just create a domain specific to that world and that's what all clerics are.

I got rid of domains, because the basis for them is "there is a god, and they are the god of this thing", and all of my gods are all gods of all of the things, but they all have common basis for the Clerics. The clerics have a specific job to do. 

So they get to choose from smite, rebukes, and similar stuff that was chosen by the gods as gifts granted.

I actually really like the idea of cleric gaining powers just through their sheer faith in whatever god they worship.
Sure, the old saying "the power was in you all along" is cheesy and cliché, but imagine a cleric finding out the source of their magic was conjured purely through their dedicated belief in a higher being, almost like an arcane "tulpa" of sorts, and how they'd come to terms with that if they found out. Would they lose access to their magic or continue to lie to themselves just to maintain access to their abilities? 
Fun concept honestly.

I would say leave it unresolved. There are so many mysteries in our own world. Why not leave the door open to similar mysteries in a magical world?

I'm also going to suggest another possible interpretation. Connecting with a domain allows the clerics to connect with some remnant of the dead gods. Like a corpse responding to an electric shock, devotion to an ideal is like a spark that causes the dead gods to provide divine spells to clerics.

In my campaign, we have something similar. My players draw power from the primal sources of those domains, and it works a treat.

Quote from AEDorsay >>

Is Divine Magic different from Arcane Magic?

the domains are "concepts" -- and some of them presume that the domain has sentience, awareness. 

One option is that each cleric doesn't take a domain, they take three to five special abilities from different domains.

Another is you just create a domain specific to that world and that's what all clerics are.

I got rid of domains, because the basis for them is "there is a god, and they are the god of this thing", and all of my gods are all gods of all of the things, but they all have common basis for the Clerics. The clerics have a specific job to do. 

So they get to choose from smite, rebukes, and similar stuff that was chosen by the gods as gifts granted.

Yes. Arcane is through study and treat magic as a science almost. Hence the rituals and the components and so on. You're directly manipulating the web of arcane energy through practices and methods passed down through texts.

Divine magic is magic granted through being favored by a god, or through the act of faith and believe. There's less science, and more prayer.

Warlocks aren't very far off from divine magic, but it's contractual and not necessarily a thing born of devotion. I do X and I get Y. 

Druids are more like wizards but also divine? They get their power through nature and the ambient arcane forces as do wizards, but it's also got this element of spiritualism in that you are doing more of an ask to the plants and other life around you that's similar to the divine magic's pray/asking of its god?

Sorcerers probably should use either the divine or primal domain spells, or more truthfully should have access to their own special list (as really should warlocks based on their pact patron) chock full of spells that just inherently use and manipulate the arcane energies around them without asking, and sometimes with unintended consequences. 

Bards just pick up bits and pieces as they travel and learn. 

Artificers are literally treating magic as science and are limited only to the arcane practices that behave as science.