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 :)

There are four great planes of existence –

• The Astral Plane – Home of immortals and the source of Shards
• The Material Plane - where the game is set, home to mortals.
• The Elemental Plane - Home of the living elements. Fire, Water, Air and Earth.
• The Ethereal Plane – A shadowy glue that sticks everything together, that is known as the World Tree

The great planes are all infinite. That means (for example) that each of the gods can create their own infinite plane within the astral plane - and it still remains one thing. The same works on the Elemental Plane to allow infinite pockets of each of the elements (or demi-elements) to exist. (Infinity is both weird and wonderful)

Demi-Planes are not infinite, but can be so large that they appear to be. A deity’s home demi-plane will grow daily - think of Greater Create Demi-plane cast at god-level with a Permanency on it – literally at the god’s will. Elemental Demi-planes work in pretty much the same way. However, if it feels better to you, call them planes and make them infinite. Play it as you will, the sages, alchemists and high priests don’t really know for sure.

The Astral Plane is also known as the 'Spirit World' Mortal flesh and blood can't live in the spirit world, although our souls go there when we die. Some mortal creatures can send their souls there, temporarily, through spells, runes and other magical means. The gods and great spirits live here, overseeing their charges on the physical planes. At one extreme are the demi-planes of hope and life (the positive planes) and at the other the demi-plane of despair (the negative planes) - but most of the gods make their homes in their own demi-planes somewhere in between. It is said that the River Styx connects all of these demi-planes together and, that if you can pay the boatmen, one of them will take you to the right place. NOTE: Positive and Negative planes are part of the astral – think of them as a type of spiritual energy rather than a physical energy.

The Material Plane is where the mortals live. It allows the combination of elements, spirit and mana that makes up a man (or a dwarf, or a tree, or any other living thing). Our plane is just one of many demi-planes that make up the material plane. Plenty of opportunity for alternate-reality settings.

The Elemental Plane – is a roiling mass of raw element and elemental energy. However, like often clumps together with like and there are demi-plane like patches (or they might be actual demi-planes or even whole planes if that suits you). Any character travelling here should be very well prepared and protected.

The Ethereal Plane separates the three great planes, but also binds them together like glue, Some sages say that the Astral, Material and Elemental planes are woven together like the threads in a cloth, and that the Ethereal fills the gaps between. But no one really for sure. What they do know, is that you can't pass from the Astral directly to the Material or Elemental plane, without passing through the Ethereal - unless you can set up an inter-planar portal of some type. We also know is that The Ethereal is (or appears to be) the source of magic.

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. the Astral – giving rise to the ‘sandwich’ map pf the cosmos. - and also also hosts The Well, home of destiny and the fates.

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 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 there are probably other names as well. However you see it, all three 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, 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 most 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 IF they absorb enough shards.

Motes – The essence of magic. Most concentrated in the Ethereal Plane, 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 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 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 cast 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. Unless, of course, the DM chooses differently :)

Most deities can select 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, because the rules cover that. For me, I rationalize those spells as coming from unnamed deities, who approve of the concept, in much the same way as Oracles receive their spells.

More interesting, 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 four trials (when they become tier 3) However, the spells that they can grant are very limited. I tend to 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 …

Sources