This is a functional, DM level, view of the cosmic structure that allows me to 'see' how everything fits together. Characters aren't really going to know about Motes of Magic, Shards of Divinity, or any of the other structural stuff on this page. Even Priests are going to describe the structure of the world and cosmos differently - using what ever words and structures that their faith thinks is right. Personally, I let characters describe the universe however they like - it rarely makes any difference to what happens :)

The World Tree or the Tree of Life. Some say that its roots in the Elemental plane, its trunk is part of the Ethereal and the branches reach into the Material and Astral planes. Which makes it one of the Transitive Planes.

The Well is also known as the Well of Knowledge, The Well of Wisdom and the World Well. It a Demi-plane located within the Ethereal plane among the roots of the world tree. Those that have ventured inside report that it is a plane of green hills and still lakes that is lit by fires floating in the sky, and that there are many gates here to the elemental plane. What is certain is that The Well is home to Destiny, the Fates, Norns, Moirai, Parcae, Ursitoare, Sudice, Rozanicy and many similar beings, who are all busy working the destiny for Mortals. Humans, Dwarves, Elves, Kobold, Orcs and all the other mortal races that are affected by destiny. Your destiny is not an end result, rather it is a path that you must tread - but how you follow it, what you make of it and the eventual destination are down to you.

Planar Portals – (do we want to call them that?) are naturally occurring wormholes between the planes. Small Portals (called Gates) can be created by powerful magic uses - but they are as nothing compared to the Great Portals. Some believe they are a natural phenomenon, others say that they are super-gates created by ancient gods. Who knows. However, beings entering one side of the Portal, come out the other side, and can thus travel between planes. Unfortunately, these portals are nearly always in places that are difficult to get to or very well hidden. Some philosophers believe that each sun contains a portal to an elemental fire pocket, while each habitable world contains portals to the Ethereal, Astral and Elemental planes. One has even postulated that a wizard could create a world by creating the appropriate portals next to each other in outer space. There is even a school that thinks the all the material planes were created in just that way.

The Miasma - The Miasma is a region close to the Prime Material, where both the Ethereal and Astral planes act differently to normal. Some describe them as ‘thicker’ others describe them as ‘more dense’, while another group describes them as ‘closely intermingled’. They all agree, however, that something is different, and most believe that The Miasma creates a sort of border plane around the Prime Material – although it isn’t consistent. It has many names and many aspects - some sages recognize it as a Border Ethereal, some as the Plane of Shadows, others call it the Paths of the Dead, and all of those functions overlap all overlap. However you see it, Astral, Etheral and Prime planes all seem to co-exist in the same space at the same time, like some twisted, not quite right, version of both planes, which have, somehow, become intermingled and interlinked.

Shards – The Shards of Divinity. When the Old Gods were destroyed their being, and their divinity, was scattered far and wide – although most of it found its way back to the astral. Some was hoovered up by the new gods, some was absorbed by the godlings and demigods who survived the wars. But many still lies scattered, or bound up in Divine Artefacts, ready to be absorbed by whoever is capable. Gods, devils and demons are particularly interested - but mortals can become Mythic, and even quasi-deities, IF they absorb enough shards.

Motes – The essence of magic. Mostly scattered across the Astral and Ethereal Planes, Motes of Magic drives spells and magical effects. Some beings - Gods, Demons, Magic Beasts, Sorcerers, Bards, etc – have an innate ability to harness Motes and cast spells or create magical effects, without assistance. Others – Wizards, Magi and other arcane casters learn long complex formulae that allow them to summon and manipulate magic. Still others, are gifted their magical powers by a deity. Perhaps one indicator that a being should be considered a deity, is the ability to grant spells to their chosen followers.

Simply put - once you can grant divine spell use to another being, you are considered to be a deity of some sort - and that ability comes from having absorbed enough Shards of Divinity. It doesn't matter if the rules classes them as a god, goddess, devil, demon, or something different - if they can grant spells, they are (under these rules) a deity.

Most of the time, this isn't important as characters don't really come into contact with an actual deity :) Even so, the powers of deities are defined within their source rules - a D&D deity follows the D&D rules, a PF deity follows the PF rules, etc. Somewhere in the rules it specifies “They can grant these spells and domains” and “They have these personal abilities” - and that is what the players get and see. Homebrew deities have their abilities listed in their personal entry on the Deities page - Unless, of course, the DM chooses differently :)

Most deities can select the spells that are available to different priests. There is Cleric/Oracle list, Paladin List, Adept list - and there are still other religious practitioners who all have other lists that are categorized as divine. Again, not a problem - as the various rules books specify what is available to whom. Nor do priests who follow philosophies cause a problem, as those spells come from ritual, unnamed deities or spirits who approve of the concept, in much the same way as Oracles receive their spells.

Note, however, that not all gods are created equal. In this world, Quasi-Deities are restricted to granting spells from the Adept Spell List, an unusual mixture (for a priest) and limited to L5 spells. Some general faiths (such as the Cult of the Small Gods) are restricted to granting spells of up to 3rd level - these spells are granted by taught ritual, rather than by the deity or any of their servants. If you are playing a priestly character, choose your deity wisely.

More interesting, perhaps, is the question of how mortals become deities - at the moment I am aware of a number of ways.

• Gift of the Gods - there are all sorts of stories where a mortal (or some other creature) has been raised to a deity by another god. For Example, 'Nivi Rhombodazzle traded a special gem to Torag in exchange for becoming a demigoddess'and of my homebrew deities, at least two (Takri and Arth) were gifted their deific status by other deities. There are similar stories in just about every other rules set. That just tells us that many deities have more Shards of Divinity than they actually need, or can gather them very quickly, to be able to bestow them on another.
• Inheritance - sometimes a god dies and passes their divinity and/or portfolio to another, for example Midnight became Mystara, in the 3.5 universe. However, it might be that a deity is killed in a fight, and the portfolio is 'stolen' by the victor. That could be another deity, feeding on the death or a peer, or a particularly powerful mortal (devil, demon etc) taking on a weakened deity and stealing their powers. Often times there will be a few shards of divinity left over, that just get lost in the ether …
• The Starstone - Pathfinder has the Starstone as a shortcut to deity. You jump across to it, face various trials and, if you succeed, become a deity of some sort. Cayden Cailean, The Lucky Drunk, is probably the most well known of these.
• Mythic Deeds - as PF Mythic characters progress, they can gain mythic levels by becoming involved in events of cosmic / mythological importance. In my system, that just means they are in a position to absorb a stray Shard of Divinity. Each 'Trial' gains them one shard of Divinity - unless the DM decides differently. A character needs something like thirty trials/shards before they are a real power. However, by choosing the right abilities, they can become a quasi-deity after fewer trials (when they become tier 3) However, the spells that they can grant are limited their Mythic Tier and Powers/Domains need higher tiers. I restrict quasi-deities to Adept spells - just to add a bit of differentiation. I miss the days when Demi-gods could only grant 5th level spells, etc …

Notes and Sources