Do the planes have to be infinite?

Short answer (well, short for me at least): It's a conceit of the game system and not really meant to represent anything coherent with regards to the real world.

From inside the setting though, I seem to recall reading about how the elementals and other natives are the only ones able to navigate on the Inner Planes with any sort of reliability and that if anybody really wants to travel around, you need to talk to the natives, otherwise you're not going to get very far. I can't help but think of the Inner Planes has somehow having extra spacial dimensions that make perfect sense to a native, but non-natives remain blind to. Moving towards Mineral from Earth makes perfect sense to an earth elemental, but given that both planes are infinite, you can't really drop down a literal border. Consider also how the Ethereal borders all of the Inner Planes. Just from that alone you can tell there's some really strange stuff going on with the spacial dimensions of the whole arrangement.

Thinking about this some more, I'd consider a sort of bound space for non-natives, and infinite potential space for natives. The bound space could expand if/when non-natives are guided to and settle in some of that infinite space. It would draw a distinction between the heavily settled areas that kind of exist at the fringe of a given Inner Plane and it's core. It could also be thought of how beliefs manifest themselves on the Inner Planes. Going from an infinite potential to something finite and realized.

Given all of that, and going back to the Mineral example, it would make sense how, even though there's an infinite space filled with nothing but precious metals and gemstones, you'd never convince a native to guide you to it. And non-natives can't inherently navigate around that infinite space, so even if they reached the plane and started mining that gold seam, they lack the ability to move into that extra-dimensional space and are stuck with wherever the seam ends for them.

Movement on the inner planes is weird, and doesn't correspond to how it works on the Material Plane. Even though they represent physical matter, they don't contain physical space in the same way the Material Plane does. They don't contain zero space like the Astral Plane, but it's arguable that, as domains within the Ethereal, much of the infinity of the Inner Planes is only potential, tucked away in some wellspring of infinite hypothetical matter continually churning out new material only to let it fade away again if no one is directly observing it. Even if it's all actual space, somehow, the fact of the matter is that it takes a non-infinite amount of time to travel from one "end" of an Inner Plane to another. In fact, it takes only 10-100 hours (The Inner Planes, page 12). That's not a big area, in any practical sense; it's (at most) four days of travel, or roughly 100 miles if this were the Material Plane plains and everyone had an average human movement rate.

So is every Inner Plane 10-100 miles across? Not exactly; they're weird. You can fit a lot more things into an inner plane than that number would suggest. You can fit, potentially, an infinite number of things. But of course no one's going to ever see anywhere near that much, no matter how many times they travel all the way from the border between Earth and Ooze to the border between Earth and Magma, or between Mineral and Dust, or even if they travel all the way from Earth to Magma to Fire to Smoke to Air to Ice to Water to Ooze and back to Earth again, a journey which takes 80-800 hours in total travel time, not counting rests. If you want to find specific trading towns along the way, though, it takes considerably longer. If you want to stop in the City of Brass while you're in Fire, you're looking at an additional 4-40 days of travel on the Plane of Fire alone, or the equivalent of traveling 100-1000 miles out of your way just to see something other than monotonous flame, then another 10-100 hours to get to Smoke or another border assuming you don't use a portal, vortex, or other form of planar travel as a shortcut.

And here's where you start to see the infinity, because even with a native guide, every single overland journey within a single inner plane takes 100-1000 hours, no matter how fine you slice it. So an inner plane is really like a small region 10-100 miles across that you can slice into an unlimited amount of 100-1000 mile chunks.

Another weird thing is that these travel times take place in directions that non-natives simply can't perceive. This has been explained as a dimension of sorts; by implication, primes (and outer planars) are three-dimensional beings and elementals are four-dimensional beings, or at least are beings who can see and travel in four dimensions. The elemental planes are infinite in three-dimensional space; you can travel across them forever and never find anything (not veins of valuable minerals, not settlements, not anything) but monotonous elemental material unless you get a hint on where the secret dimension is (which you apparently perceive as one of the three dimensions, but isn't), in which case places are suddenly findable. So a non-native can travel across the Plane of Mineral for centuries and never find anything but relatively worthless crystal. If they meet an elemental or tsnng, it's because those creatures were able to detect a non-native and deliberately sought the sod out. And it's going to take them 100-1000 hours to get to you, no matter where in the plane they were initially, so it'll be a while. You're not going to meet anyone accidentally, not unless you're in a settlement. That means, except in settlements or other sites of interest, there should never be any random encounters on the Inner Planes for the first 100 hours the party is there. Jem's suggestion that elementals are created by intruders is interesting, but even granted that, the party isn't going to meet anyone but elementals for a good few days. 'Course, if they got there via a vortex or portal, they're starting out in a place of significance, and there might be guards or what have you already posted nearby, ready to either start an encounter right away or follow the party at a discrete distance to meet up at a time of their choosing.

Now, you don't always need a native guide. An elemental compass won't help you find any place or person in specific, but it'll get you to the next plane over if all you want is to circumnavigate the Great Wheel or get the hell out of Dodge. A beacon seed is magicked to get you to one place in particular, so you can use it to find the City of Brass from anywhere else in the Inner Planes, but then you'll need a portal, vortex, a compass, another beacon seed, or access to the Ethereal to get from the City of Brass to anywhere but the infinite trackless wastes of the Elemental Plane of Fire.

Anyhow, looking at the Inner Planes in terms of percentages isn't going to get you anywhere. If the Quasielemental Plane of Mineral is 10% pure diamond, then that 10% of the plane is completely unfindable to anyone except a native or someone with a beacon seed. And to make a beacon seed, you need to have visited the diamond vein before, which means you need a native guide. The population of any inner plane is probably finite. A finite number of elementals is plenty to reach any point worth visiting on the infinite plane. Any settlements on the plane are probably located around a portal or vortex (or, I suppose, a vein of valuable minerals or the like), so that non-natives can find it and locals have a way to get somewhere else. There are probably a few settlements where the founders got lost and found a way to survive wherever they happened to be, eventually producing something worth the natives' time in visiting and guiding others to.

One point I want to make that I think often goes overlooked with this economic challenge to an infinite multiverse is that as long as it still takes a given set of time to exploit an element, there will still be supply and demand. Given the labor and material costs involved in the exploitation of any good, you can still reasonably expect a market to exist. Even in the real world, we have weird market dynamics wherein incredibly abundant materials like diamonds still have inflated prices because of labor costs (or more strictly the costs of production) and the existence of effective monopolies wherein the supply of goods is tightly controlled. Even with an infinite supply of any given resource, as long as we assume labor is limited (and perhaps that "rarer" minerals are more time consuming to harvest) and a desire for elementals or other creatures seeking to exploit minerals to serve their own interests, they have reason to control their market tightly and maximize profits (especially when you add in the danger for not natives). If there is a limited supply of labor, the market would still demand various prices based on the difficulties in extracting the raw material. Prices might be reasonably stable, since the conditions of extraction would pretty much remain fixed (although the politics surrounding various enterprises may have some impact), but there would still be a cost. Interestingly, that would mean prices would more closely reflect a labor theory of value ala Marxism, which makes for all sorts of neat political and philosophical conflict.

Personally, I find answers to these types of questions that are sort of intrinsic to the mysticism of Planescape to be much less compelling than the questions. Planescape defies the physics of our reality, and much of it is designed to present players with Big Questions rather than merely technical obstacles, so it's difficult to justify the strict application of our own understanding of physical reality (or metaphysical reality for that matter). You can always posit solutions to these questions certainly. (Another possible answer to your question is that the planes have an infinite surface with a finite space ala Gabriel's Horn (which can double as a badass Artifact), which may make it easy for a native to navigate who understands or can perceive the shape of their universe, but no so much for the clueless traveler, and it also ends up a convenient explanation for the fixed travel times and the possibility for infinite wandering if you are going in the wrong direction despite a fixed area). However, I think having an answer to that kind of built in planar paradox ends up robbing it of some of its mystique (much like wanting to stat the lady of pain).

I guess my point is, whenever you dig too deeply into requiring a "rational" explanation for things that are only bound by the imagination, and which don't actually follow any strict set of rules that can be materially determined, you don't really get very meaningful answers, you just get new questions. That can sometimes produce a really interesting idea (I like much of what Rip and Jem suggest for example), but unless it somehow pertains to the story of the planes, I'm not sure an answer is really necessary. If anything, I think the question itself is far more compelling than any particular answer provided (and unique to Planescape, the conflict inherent in the factions and multiverse that exists in trying to resolve these sorts of questions). I would rather have various parties offering up all the explanations provided (Guvners suggesting elementals as 4 dimensional beings, signers suggesting elementals are actually created by virtue of the presence of a mind, the Bleak Cabal suggesting there isn't any answer to be found and so on, each a valid idea in the planesape context), with the interpretation ultimately up to the players. When the DM has a strict interpretation of these things, it tends to suggest a particular view of the multiverse is unambiguously correct, which robs the world of much of its flavor. It would be akin to having (a) God come down and tell us that actually as it turns out, the Zoroastrians have the right of it.

To give an analogy, while it is fascinating to know how our own universe works in ever greater detail, that knowledge is not often necessary for a story to be told, even if it does occasionally play a role, and ultimately there are a lot of very good challenges to even seemingly well footed materialistic explanations of the universe (Wittgenstein comes to mind). In Planescape, the questions are often what drive the story forward. The answers are often far less satisfying. I think that was the thrust of the joke of Douglas Adam's series, wherein the answer to the meaning of life was 42. No answer to any big question is likely to be as mystical, transcendent and compelling as the nature of the question itself, and trying to give a concrete answer to something as philosophically challenging as the paradox of infinity is to me I guess off the mark.

Idran: I indeed did not read the rest of it. However, speaking of that now, I feel that both the TC as well as Ripvanwormer and several other posters in this topic are delving too far into physics, which should NEVER be done in D&D, for two main reasons
1. The mechanics and fluff of 1-3E already defy physics to a ridiculous degree. Especially the entire Spelljammer setting.
2. Attempting to make D&D adhere to physics will ruin the gameplay and make things overly complicated. For instance, what are oozes? What happens when you cast Wall of Fire within an enclosed space which doesn't allow the heat to escape? Will this double the damage and extend the range of damage? How about the acoustics of a Shatter spell when taking into consideration the terrain, weather (is there cloudcover?), etc.? Shouldn't practically all materials be reduced to a Hardness of 0 when exposed to the -100+ temps of the Paraelemental Plane of Ice? What about expansion due to heat and shrinkage due to cold?

Also, I feel, once again, that trying to explain WHY the planes are infinite to non-natives ruins the mystery of the plane. Not to mention that unless a native and an outsider can practically mind meld, it's not going to be possible for either one to figure out, even if they swapped physical bodies.

As I said, I don't see how this could possibly work unless you had a spell that temporarily made the target a native of the plane, which might have some game-breaking effects. Actually, I'm quite certain it would have game-breaking effects, since it would basically render you immune to any and all planar traits, effects, etc., even those otherwise impossible to protect against if one is not native, such as True Cold zones on Paraelemental Ice. It'd also be broken in that it would allow the recipient to craft magic items that only a native of specific planes can create.

Part of the issue of Planescape is that the setting itself represents a large logical inconsistency, in that all the faction philosophies are treated as being more or less equally valid. Logically speaking, the viewpoints of various factions should be mutually exclusive (unless you embrace paraconsistent logic anyway). Planescape sort of halfheartedly resolves this with the hand waving explanation of "belief shapes the multiverse", which does manage to explain why competing philosophies can all seem to "work" in some fashion or another.
I think trying to reconcile the inherently logical contradictions of the setting is impossible without denying the very essence of Planescape, that being the clash of ideas wherein no idea is given special preference.

You seem to expect that the inner planes conforms to some sort of law that we can both understand as humans and apply consistently as gamers, as opposed to them simply having an entirely inscrutable system by which they operates, only some of which can be divined by virtue of the limitations of those traveling the plane. It would be like us being aware that things fall when you drop them, but not being aware of gravity as a force. Personally, I think both are equally valid perspectives, and I don't see why either would have any particular impact upon verisimilitude. After all, people told plenty of great stories long before there was a clear understanding of how things worked on our planet. In fact, lots of really great engaging stories originated out of misunderstanding!

On a side note I find your comment about the Guvner's being "more right than they could possible imagine" to be amusingly meta. I assume you mean to suggest that the Planescape world actually works according to the rules used by the gaming group, and thus the multiverse conforms to a fixed set of rules. Of course, it means the Signers are right too. After all, nothing in Planescape exists unless we imagine it into existence

Anyway, this has been a real interesting discussion. Just wanted to bring up those few final points.

That's not half-hearted. It's the primary theme of the setting. The war between beliefs, to determine who shapes the multiverse, is Planescape.

It's whole-hearted.

What I mean by half-hearted is that it doesn't really reconcile the philosophical contradiction (namely, belief has to spring from somewhere, but all things are apparently shaped by belief, including those who generate belief), not that it isn't a fleshed out idea that produces really cool stuff. I love the setting that results from this, I just mean to suggest Planescape doesn't really lend itself to the strict logical construction that Idran seems to be desiring.

That's easy to explain. In the beginning, there was only the Ethereal, an endless void, and the Draeden (sentient, Cthulu-like beings left over from the destruction of the previous creation cycle/multiverse) Ethereal (potential) births the Elemental Planes (matter and energy) and the Astral (belief) At this point, only the draeden and, to a degree, the Ethereal are there to shape belief.
Belief acquires sentience to form the first powers of the multiverse.

Short answer: belief, like everything else, was originally spawned by protomatter from the Ethereal.
What spawned the Ethereal? Who knows. In all likelihood, it was always there. After all, the Ethereal Plane IS possibility and potential.
The pious who come to this realization are likely to practice a planar form of Gaiaism, worshipping the Ethereal itself as the great creator and the source of all potential and possibility.
Others are likely to worship Ptah for whatever reason (some viewing Ptah of course as a manifestation of the Ethereal's will or power)

I think you're linking together two different things. Belief, broadly, is a shaping force, not a creative force. Although some (or possibly all) gods seem to have sprang from belief, the multiverse itself isn't said to have originated that way. Belief is power, so it's thought that enough of it can transform an essentially chaotic multiverse (as the Xaositects believe) into an essentially lawful one (as the Fraternity of Order would have it), or a multiverse based primarily on magic (as the Incantifers believe) into one based primarily on financial transactions (as with the Merkhant ethos), but it doesn't actually cause the multiverse to come into being.

By (extremely rough) analogy, imagine if you'd said, "If the Big Bang can generate the building blocks of existence, why introduce this unnecessary secondary creative force called gravity?" Gravity shapes galaxies and planets, but it's thought to have emerged later in the cosmology after the primal unified force separated into the different forces known today. While no one doubts that gravity exists and plays a role in shaping the universe, no one's claiming it's responsible for the creation of everything. That doesn't make it "half-hearted" to discuss gravity and its cosmological role.

The role of belief in Planescape is, I think, similar. While the war for the dominance of one belief system over the other is fundamental to the play of factions, sects, and planar entities (including the struggle between the tanar'ri and baatezu to determine the nature of evil) and is the heart of the Planescape campaign setting, I don't think any source ever claims that the multiverse itself came into existence because someone believed it into being. That would indeed result in a problem like the one you cite, because where did the first believer come from? But I don't think that's the case.

The draedens didn't create anything. They were creatures of the void, and desired only void. The creators came along later. The draedens warred against them and lost, so most of them went to sleep, to wait until there wasn't anything but void any more.

That's deliberately ambiguous, as it should be. I think what you mean by this is you're asking, for example, if the Guvners think the multiverse is orderly and the Xaositects think it's chaotic, what is it really? And the answer is maybe that it has traits of both, because neither faction has "won." And that is difficult to imagine, and yes, I agree with you with your basic point that this means Planescape isn't necessarily as self-consistent as Idran maybe wants it to be. The Guvners imagine a multiverse that's fundamentally logical and self-consistent, as Idran imagines, but the Xaositects and Bleak Cabal imagine a multiverse that might be fundamentally arbitrary and paradoxical, with no consistent laws or logic behind them. And the truth is, perhaps, somewhere in between.

And I'm going to contradict myself somewhat on this point further down. Really, the Xaositects don't think they're making the multiverse more chaotic through their beliefs. They think the multiverse is chaotic, and their belief in this fact gives them power. But the multiverse would be chaotic regardless of what they think, and regardless of whether or not they have power or not. They freely admit that the Guvners' beliefs bring them power as well, but they're still wrong.

And perhaps they're right. Maybe the multiverse really is arbitrary and paradoxical, no matter how much the Fraternity of Order wishes it wasn't the case. Belief is powerful, but it's not at all clear it can completely reshape reality.

For my part, I didn't really advance a theory of what distance "really" was in the Inner Planes as just describe how it works according to The Inner Planes supplement. One amendment to my speculations above that I would make is that I failed to account for the power of fate, destiny, chance, and coincidence in a fantastic multiverse. With that in mind, someone probably could stumble upon elemental beings or an entirely settlement, apparently randomly, even in an infinite plane, even without the aid of an elemental guide or beacon seed. It'd be impossible if you were assuming mathematical odds were the only forces at work, but they aren't. Destiny is in play.

Well, there are "belief points" in the Planewalker's Handbook, so yes. At least in a metagame way.

The Primal Order game, designed by Wizards of the Coast founder Peter Adkinson as the company's first product, postulated that gods gain power from "primal energy" that can be produced both by the belief of worshipers and by the planes themselves. Each worshiper produces one point of primal flux per day, as I recall. The game was big on spreadsheets (gods get a number of flux points determined by their number of worshipers and the number of planes under their control). In that setting, primal energy would be the first force in the multiverse, and belief is only one aspect of it.

I think of it as the substance the Outer Planes are made of. Note that the multiverse as a whole probably predates the Outer Planes. In its rawest form, there are the "thought winds" and ectoplasmic mists of the Astral Plane. Eventually, over eons, these collect to become "astral dominions" or Outer Planes.

The question is whether or not belief is the same as the substance that makes up souls. It could be that "spirit" is merely a substance extremely vulnerable to the power of popular opinion. If that's the case, the Outer Planes are probably made from both belief and spirit-matter that has been shaped by belief after migrating to the Outer Planes.

I imagine this is illustrated most vividly when a cleric turns or commands undead, or when two anarchs in Limbo attempt to create terrain directly at odds with one another's intentions.

Normally the relevant variables to determine whose belief is "better" would be wisdom (force of will, essentially mental endurance) or charisma (force of personality, or mental strength), though character level (representing belief honed by experience and hard work, as opposed to the relatively naive, untested and ignorant belief of low-level characters) is also an important factor.

Note that there's no true distance in the Astral Plane, so any belief that collects there needs a range of only zero. Still, there's a form of conceptual distance even in the Outer Planes, inherent in the nature of specific beliefs, and ideas that are conceptually distant from one another (for example, vice and virtue) are located a long ways apart.

On other planes, like the elemental planes or the Prime, it's much less clear if belief can truly transform the nature of reality, how much belief it would take, or if reality would be changed everywhere or only locally. The subjective gravity of some inner planes is sometimes cited as a result of the power of belief, although if one person's down is another person's up, this remains true only for that individual. It seems to be impossible, in the inner planes, for any number of people to force an individual to accept their own interpretation of what "up" is, and in this respect it seems that belief is not power in the Inner Planes.

That's not going to stop anyone from trying, however. And who's to say? But the possibility remains so theoretical you don't really need to come up with a concrete answer.

Ha! I originally read this as "Say I believe no beliefs exist." That is, "My opinion is that I have no opinion about anything, and neither do you. I have a very strong opinion about this opinion that I don't have." The power of stupid people in large numbers should never be underestimated, so I'd say this is possible, though unlikely. The more people believed that they didn't believe what they were believing, or anything else, the more it would be true (perhaps). They would come to believe things less and less, and eventually their opinion would cease to matter.

Or, alternately, their opinion never mattered. They would get lots of belief-destroying powers that might give them advantages against rival factions, but it wouldn't change the way the multiverse really worked. The Outer Planes are made of belief, and that'd be true regardless.

As for your actual statement, someone believing that no one has an antithetical belief system, this really isn't different from someone believing their belief system is the only right one, and it has the same resolution. The belief has power relative to the proportion of sapient souls who believe in it, and the relative power of their belief (factoring in experience level, charisma, wisdom and so forth, although on average this won't make enough difference to worry about). If everyone in the multiverse believed in a single philosophy, and believed no other philosophies existed, they would be right (obviously). This is the goal of the Harmonium.

I'd say both are true. It's produced by minds (more properly, souls) and it also exists independently in the form of the substance of the Outer Planes. Belief may well have existed before there were any minds, just raw Law, Chaos, Good, and Evil whispering at the edges of the Astral Plane in the beginning of all things.

Are you asking if minds are able to imagine impossible things, or are you asking if they're able to think in situations where thinking is impossible? To the former question I'd say yes, but to the latter question I'd say no.

The Bleak Cabal would probably agree with this, but other factions usually agree that thought has an origin and destiny relevant to their conception of the multiverse. The Godsmen believe it comes from the Source, the Athar believe it comes from the Great Unknown, the Xaositects believe it springs from chaos, and the Dustmen believe it came from True Life in the time before time, before everything died, to give some obvious examples. The Transcendent Order doesn't think about such things, but they feel them. Other factions might default to whatever other religious or philosophical structure they follow.

The Fraternity of Order might agree with you there. As I said above, I don't think belief was ever intended as a multiversal creative force.

Yes. With enough belief, you can take things that were formally less true, and make them more true. For example, if enough people worship a fictitious god, eventually it will become a real god. It's possible there are some things that won't be true regardless of how much people believe they are ("this statement is false.").

The Guvners believe it does.

Belief does. This isn't really as circular as it sounds, since "belief" is usually found in the form of concrete philosophies, not generic appeals to "belief" as an inchoate, hand-wavy something-or-other. That is, people believe in specific things more than they believe in belief itself, and these specific things normally have their own boundaries in accordance with the ideological system they're part of. Like, where does Christianity begin and Judaism end? Most people would agree that it's fundamentally a disagreement about the nature of the Messiah and what salvation requires. And because people believe it, it's true. Some beliefs may have vaguer boundaries than others. That's fine. Some countries have vaguer boundaries than others, too: that doesn't mean the countries aren't real.

No.

Most people believe things because they think they're true. Most planar factions are aware that belief shapes reality to some extent: they only have to look at the way gate-towns slide into other planes when their philosophies change to have proof of that, not to mention faction powers. And they're willing to use this as a tool, and they acknowledge that rival factions have power because their beliefs give them power. But they don't believe beliefs have so much power that they alter the fundamental truths of the multiverse. Could you cynically spread a false belief in order to benefit yourself? You could, and they probably believe that's what most of the other factions are doing. But it wouldn't get you closer to the true nature of reality, which is where the real power lies. Living among the souls of the dead in the afterlife gives you the perspective that transitory power is all well and good, but eventually you're probably going to end up a petitioner with no memory, and it'd be good to know what comes after that, because by itself that's a pretty meaningless end to it all. So what's the real point, beyond the petty squabbles of the planes? It's important to know.

Some of the factions are deliberately trying to use belief to manipulate reality: the Harmonium, definitely. They believe that the power of consensus will make the multiverse harmonious. But they believe in a fundamental truth, that harmony is preferable to disharmony, and believe this is true regardless of what other people believe. Most of them just believe things because their beliefs make sense to them. That's why the Dustmen, Ciphers, the Sign of One, and Bleakers don't bother to proselytize. They don't care if anyone agrees with them or not: things are the way they are. The Sign of One believe that belief is power, but only one person's belief. Which is probably one of them.

The obvious question this raises is: if most people don't believe that belief is power, then shouldn't they be mostly right? Wouldn't the power of belief rearrange reality to make itself less powerful... and therefore be less effective in rearranging reality to make itself less powerful? Possibly, but that's a paradox, so it probably doesn't have any real effect. And most planars, at least, do believe belief has some power.

The conceit of the setting is that belief matters. The reason for this is that the Outer Planes are made of belief, and therefore malleable by belief. And entities and forces on the Outer Planes can affect other planes of existence: the gods created on the Outer Planes can create and destroy worlds, and philosophies can be as powerful as gods. Even if a philosophy isn't personified in the form of a god, it can have many of a god's powers without that pesky willfulness. And when the tanar'ri win a victory in the Blood War, every being with a soul becomes that much more chaotic than it was before. Every time an angel is corrupted, every being with a soul becomes that much less virtuous. Every time a fiend is reformed or a gate-town is dragged out of the Lower Planes, everyone becomes slightly less evil. That's why the Outer Planes matter, and one of the reasons why belief is power. Belief can change the Outer Planes, but the Outer Planes can also change belief. The Unity of Rings proves this.

The Dustmen are a powerful force in Sigil because they have a powerful belief. If you ask them, they'd probably say their belief is powerful because it's correct, and other factions may have power because of nature of the planes rewards belief, but nothing they believe will change the fact that everyone is dead and True Death is the only release from suffering. The Xaositects acknowledge that the Guvner belief in laws gives them power, like the axioms and loopholes they exploit, but their beliefs don't change the fact that laws are ultimately arbitrary manifestations of chaos. And so it goes.

The problem of pain is the core justification for most of the factions, which is probably why the Lady of Pain is the setting's symbol. Each faction has a different answer to the question, and each faction really exists for the sake of answering that question.

The Bleak Cabal has decided that there's no reason for there to be suffering, and the only "solution," such as it is, is to embrace that fact, accept the meaninglessness of existence, and help people where you can. This doesn't mean there won't be any suffering, but they can reduce it a little both through acts of charity and not wasting effort trying to find meaning where there is none. Suffering exists, and there's no rhyme or reason behind it.

The Dustmen has decided that suffering exists because Creation has fallen into death, and the solution is to learn to see beyond the illusion of life.

The Harmonium absolutely believes that sufficient belief could relieve the worlds of suffering, so their goal is to make sure everyone believes the proper and sufficient things.

The Ciphers believe suffering can be avoided if thought can be eliminated.

The Doomguard believe suffering is part of the multiverse, and suffering will end when the multiverse does. Some of them believe, therefore, they should speed up the end of the multiverse, while others believe that would only increase suffering.

If someone, perhaps a Hardhead, were going to try to convince a Bleaker that they could eliminate suffering entirely if they only believed in the right things, the Bleaker would probably gently try to convince the Hardhead she was terribly, tragically wrong. Belief is power, sure, but ultimately meaningless, as all things are.

They're trying! I don't agree that the number of tanar'ri is truly infinite, however. The tanar'ri are a manifestation of belief, so they and their beliefs are only as powerful as the belief in chaotic evil across the multiverse. So they seek to spread belief in chaotic evil by tempting mortals into their path and simply making the multiverse as chaotic and evil as they can. Every time they wreak destruction and woe, they get stronger. Every time they physically steal part of the landscape of the Outer Planes and drag it into the Abyss, they get stronger, because the landscape is made of the beliefs of millions of souls, alive and dead.

Some beliefs are more convincing than others and therefore more successful than others. The personifications of the alignments work very hard to try to make the philosophies they represent seem more convincing. The celestials work to be inspirations, while the fiends work to be inspirations too, in their own way.

The only reason not to think that beliefs are numerically oriented is the idea that there are more tanar'ri than there are anything else. But they only manifest that way because of the nature of their beliefs, which is chaotic and fractious. The unified, focus belief of the baatezu is just as effective, so their race manifests itself in more limited numbers, as is appropriate for their more systemic and coherent belief system. Probably the eladrins and slaadi are every bit as numerous and fractious as the tanar'ri are.

So it's mostly about numbers, but not entirely. If it was entirely about numbers, then there wouldn't be much point in doing things like dragging gate-towns across planar boundaries, or physically working to slaughter gods, devils, demons, and angels. Those things matter too, because they're powerful manifestations of belief. A single gate-town, or a single god, might be equivalent to tens and thousands of Primes with an opinion about something, because it's a concentrated, potent symbol that's been forged from the beliefs of millions.

It's interesting to think about, isn't it? I certainly can't claim you haven't been thinking about the subject, though I don't agree on all of your assumptions or conclusions. Maybe because I'm brilliant.

Or maybe you can't, but I can.

That still pushes the problem back to the creation of the Ethereal and the Draeden themselves without providing an explanatory framework.

No it isn't. Ethereal = potential and possibility personified. Potential and possibility is always there, and therefore the Ethereal has always and will always exist.
This is not anything like creationism or the big bang theory (e.g. where did god/the matter in the singularity come from)

At some point you have to say "well, something or other apparently created itself
No. Ethereal = possibility. The POSSIBILITY has always been there, in one form or another, even if it was only a sort of Ethereal singularity or spark (the possibility of possibility, so to speak).

Also, it is hard to imagine why the Draeden wouldn't have created a universe that was entirely self serving[i]
They weren't the sole arbiters of creation, they were the sole arbiters of armageddon (of the previous multiverse). They already had a multiverse that was self-serving-- primordial nothingness.

[i]And also it becomes difficult to imagine how competing beliefs reconcile
It doesn't even have to be belief. While Astral is belief personified, that is not ALL it is. It is also memory. Beings can also be created from primordial memory on the Astral.

""And also it becomes difficult to imagine how competing beliefs reconcile""
That's deliberately ambiguous, as it should be.
Agreed 100%. However, if you want to go by the evidence from the inner and outer cosmology itself, the answer is that all belief has an effect, and that the result of all these competing beliefs create an equilibrium and prevent philosophical, cosmic, etc. entropy. So in other words, every sect and faction has the right idea and the wrong idea about the multiverse, because their beliefs help shape it, but are not the be-all end-all of what shapes or guides the multiverse.
Equilibrium has not always existed; sometimes chaos has been stronger than law and vice-versa, and sometimes fire has been stronger than water, etc. In the D&D setting however, the multiverse has come to an alignment and elemental equilibrium.

Do certain beings beliefs outweigh others.
On the cosmic scale, no.

Belief may well have existed before there were any minds, just raw Law, Chaos, Good, and Evil whispering at the edges of the Astral Plane in the beginning of all things.

Actually, no. Evil and Good as concepts did not exist until some time late into creation (would have been around the time when Yugoloths were created). The concepts of Law and Chaos came far later than that.
Does that mean that actions and things which we categorize as lawful/orderly, evil, good and chaotic did not exist before those times? Of course it doesn't. It simply means that among sentient life and thought, the concept of "good vs. evil" or "law vs. chaos" did not exist, just as such concepts do NOT exist in the Far Realm, or among the Draeden, originally.

[u]Does thought spring from nowhere, in which case it is hard to explain thought as being anything other than purely random, and consequently all product of belief is without meaning or purpose?[/i]
Belief would have first sprang from protomatter and have been entirely under the influence of the Ethereal until the Astral came into being.

Well, I am not so sure I agree with that assessment. I think this belief thing as shaping force is just a giant problem if you really look closely at it.

Lets do a little thought experiment. Suppose there are six men in the whole multiverse (We can imagine they are the first six sentient being in existence). Also suppose that each of the men are equal in belief, and that the combination of two men's belief is sufficient to produce change. Two men believe there are 3 apples and 3 apples only, and another two men believe there are 4, and two other men think there are 5. In a multiverse with no other believers, If all are equally strong in belief, how many apples exist given these competing beliefs that are all equally possible but mutually exclusive propositions? Only one couple can be right, and if belief shape the multiverse but if the weight of their beliefs are equal, it should seem that no particular answer could be found, after all any one being right causes a contradiction if belief is numerically equal in effect. Whatever the various beliefs floating around, there will be only one result in a case of mutually exclusive propositions.

Ah, but perhaps they can all be right, because each one's idea of apple is a little different, so each person has their vision of apple created. Problem solved, right? After all, each person could then manifest their own apples in accordance with their belief, thus reconciling both the requirement of the particular number of apples and their own vision of what constitutes appleness. Perhaps each couple has a slight variation on appleness as compared to the next. But if we accept that belief only manifests change in sufficient quantity, then no manifestation of apple should ever occur, because of minor variations in each persons belief within any particular belief grouping. After all, beyond just the differences in belief concerning number of apples, any couple will have a slightly different notion of what an apple is when conceiving of their belief.

This could be resolved by appealing to a sort of Platonic Ideal of appleness, wherein people get their idea not from their own individual and completely unique experience and makeup, but from some universal form that exists outside the self, perhaps residing in the Astral. But this opens up a new problem, in that there must be an idea for all possible types of apples (after all, each person some how had a different idea of appleness that was still somehow possible), and indeed for all states of apples reflecting all possible ways of thinking about appleness, which perversely just recreates the problem of infinite variation in conception of appleness, such that we are liable to never to have two identical views of apple, and thus never sufficient belief to generate an apple (plenty of people have torn apart Platonic ideals if you are looking for more eloquent, exhaustive or analytical takedown).

Now, if appleness is a thing in itself, that is there is an idea of apple that exists true and pure and independent of any physical reality from which all people derive there appleness, then people should not be able to conceive of anything but the same ideal apple. If however apples are a thing in themselves, and the idea of an apple is derived from the experience one has with apples, then each person ideas must be necessarily idiosyncratic (if you need a good example of why this is so, see Wittgenstein's Beetle thought experiment). This being so, belief would be inherently unable to affect change as a product of number, because all belief would be idiosyncratic, and thus no belief would be able to produce a collective result.

Now one possible counter to this view is that all possible variations of a thing exist as an idea. But this solution produces its own conundrum. It is perfectly possible for a person to think that an orange is an apple, until demonstrated otherwise through experience. But if idea itself is derived from archetypal truths, it should not be possible for a person to conceive of an idea that is inherently perverse or which produces a falsity. The notion of an apple being a thing which possesses the characteristics of an orange is not propositionally untrue. It is only untrue in reference to the factual nature of a thing commonly understood to be apples. The only thing that can reasonably be concluded is that the notion of apples is contextual upon common understanding, even though the apple itself must exist regardless of what we decide to call it. There is no reason people should not be able to hold all sorts of beliefs that are contradictory and counter to fact because the origin of their belief need not be conditioned by the fact itself, but which are condition by their own experience which may be counter-factual.

You may try to argue that variations on belief produce an apple cumulatively that possesses the mixed traits of belief, but then again you create a problem, because that would mean apples would incorporate every wrong impression of an apple, and even contradictory opinions on appleness, until you are liable to have something not much like an apple at all. Further, it would imply the multiverse lumps together unlike things that are categorically inimical to one another simply because of a quirk of language, at which point drawing boundaries on groupings becomes messy if not downright impossible.

If belief is a shaping force in the universe, how can you really resolve this paradox? You can't have belief without ideas, and unless ideas are derived from a single universal source (which I believe is the case via the Astral in D&D), then belief should never be able to be accumulated. If on the other hand belief is derived from a universal source of ideas, then differentiation should prove impossible, or if it is possible, simply should produce the same problem created by idiosyncratic ideas not accumulating to produce a particular outcome.

To further the thought experiment, lets just say that there are in point of fact 4 apples on a particular table, and that those six men all now believed there are 4 apples on that particular table, although they are in another room not looking at the table. Then suppose another man exists in the multiverse with otherwise equivalent properties to any one of these six men. What if he then eats one of those apples? If they still believe there are still 4 apples on that table (and they would have no reason to revise their opinions being ignorant of this act), the action of this one individual just altered the structure of the universe contrary to the belief of everyone else. Does this mean I didn't eat the apple? Is a new apple created on the table, springing forth from the common belief? Are there both 4 and 3 apples on the table? The same problem applies if he attempts to place a fifth apple on the table.

There are at least two discrete possible answers to that dilemma (and a couple more messy answers). If belief shapes reality corresponding to its prevalence, no matter what action this new man takes, there should be 4 apples on the table so long as the belief is retained. There is no reason for that belief not to be retained so long as his eating the apple is known only to him. Thus, nothing done in private that contradicts public belief should be possible, which means any change to physical reality contrary to the popular conception is simply impossible.

If on the other hand eating the apple does reduce the number of apples on the table from 4 to 3, the actions created a situation contrary to popular belief, which suggests belief can't shape reality contrary to the actions of physical reality. But this creates a new problem, because it suggests actions produced in physical reality trump belief. But if this is true, it would seem there are very few actual scenarios in which belief would shape reality, because reality itself is filled with matter in a constant state of action that according to these conditions must take precedent over belief (unless we are to try and imagine an entirely new way of physics in D&D as some sort of solution, but if we try to remain logical then it is hard to imagine consistently applying such a comprehensive overhaul to the very nature of reality). After all, physical interaction with an apple trumps the belief of the multiverse, so it follows that the action of any given atom or molecule or any particle of physical reality trumps the action of belief.

We might again invoke some sort of outside system for resolving this paradox, maybe by saying on the actions of sentient actors trump common belief, but even then, any area outside of sentient interaction (and how do we define the limits of that really?) would be in a state of stasis when no sentient actor involves itself on it. Fires shouldn't spread without an audience. Objects shouldn't fall during an earthquake unless someone is watching them.

A different problem arises when belief reflects things that are not explicitly quantifiable. Any belief in an abstract or an uncountable can't really have this system applied to it. Belief in Red or Shape can't really be settled numerically, since these things are both qualities possessed of things and shaped by the experience of the observer, but yet it is perfectly possible to believe in the existence or lack of existence of subjective experiences and qualities. Is the attribute of quality then in the thing of itself, independent of any particular belief? Is subjective experience shaped by common belief? How do you then translate a quantity of belief into the existence of a particular quality? If I believe in roundness as a quality on its own, independent of a particular object, does the idea count as a discrete unit that requires a fixed set of belief? What are the boundaries for idea in terms of the quantity of belief needed to manifest it? Mustn't roundness exist in the thing itself? If it doesn't, it stands to reason that no objects can ever have stable relationships because the very nature of the laws shaping them are fluctuating.

In my personal view, you are really just better off not worrying about potential contradictions and paradoxes and instead just living with the rules and accepting that outcomes may occasionally be absurd if probed too deeply. Provide explanations sure, but don't labor under the false that an immediate solution to a particular problem resolves the larger contradictions of the multiverse. I guess my take home point is this. Much like our universe, the multiverse exists, and it seems to have certain rules, but those rules exist in and of themselves and are not contingent upon the understanding of a particular sapient species. They will operate regardless. We as observers may try to understand the rules, but just because we sometimes don't, or believe we observe a contradiction, it doesn't mean we are right. It may even be more sensible to assume you (or the player) are the one who is wrong. After all, the multiverse is going to do its thing regardless of whether or not we agree with it. Unless of course we get enough somebodies to disagree right along with us

about the only belief that will affect them, short of formalized magic or psionics (which might be an application of belief, or might not; it doesn't really matter in general, though in a specific game it might be fun to pin down), and then only some of them. In particular, "apple" is generally agreed to be a collection of mostly Water, with a bit of Earth and Positive, and touches of Fire and Air, or wu jens would give you a different elemental breakdown which was also correct as far as their standard model goes. Beliefs don't usually generate material things. Sigil's factions don't argue about whether there are 3 apples or 4 apples, and most of them speak a common language in which the notion of "apple" is reasonably well-defined by common experience.

That is correct. The only other thing that could possibly be affected in a major way by belief on the Inner Planes are the powers, but since most of these powers are primordial, it's unlikely that belief affects them in the same way that it affects most on the outer planes (for instance, Kossuth won't die if he lacks worshippers). Some argue that belief shapes the associations between elements and abstract ideas, though.

I've little to add at the moment, but that certainly was a fascinating read NichG.

I'm intrigued by this, and want to talk about it, so please bear with me if I over-narrate.

There are basically three kinds of cosmologies: steady state (always there, no beginning or end), linear (both an ultimate beginning and a final ending), and cyclical (a definite beginning and ending, but each beginning was preceded by an earlier ending, and each end makes way for a new beginning).

It sounds like you're suggesting that the Ethereal Plane itself is a steady state cosmology, while the rest of the planes are cyclical. That is, the Ethereal Plane is continually forming demiplanes that eventually evolve into full inner planes and material planes/crystal spheres. Eventually these other planes age and die, and new planes are born to take their places.

Under what circumstances, in your view, does a plane die? If the Ethereal is the only continuous plane, every other plane must die periodically. If the Ethereal is eternal, there was never a time that wasn't after a still earlier creation cycle... unless you're assuming that there was an infinite amount of time, before any other creation, in which the Ethereal Plane was sterile for an infinite duration, and you're left having to explain what might have fertilized it.

Do planes die of old age, slowly expanding and losing integrity until they crumble? Does the Ethereal itself eat away at their base, devouring the Inner Planes until they're entirely dissolved into the mists, at which point everything else collapses? Do the other planes all die at once or do they die independently of each other, one Astral dying even as two new transitive planes spring forth as substitutes? Do the draedens periodically wake up and wreck everything? Were there always draedens, or did some previous cycles have alternative arbiters of Armageddon?

My own view of multiversal history has the Far Realm as a steady-state universe, and Time (which contains the potential for the Great Wheel cosmology within it) possibly budding off it as a waste product from some unfathomably vast Far Realm creature. There's room for epochs where even potential dies, leaving nothing at all. There's also room for cycles, but there may have been a first cycle, and there may yet be a last cycle.

I think it's possible that the Astral and Ethereal actually had separate origins, but at some point they collided and stuck together, like ancient one-celled organisms made by multiple more primitive organisms joining in permanent partnership.

I think a crystal sphere is created when a demiplane is exposed to the energies of the Astral plane, pulling it across the planar boundary into the phlogiston, which crystallizes, forming a solid bubble of crystallized phlogiston due to the energies at work, incidentally protecting the reality within from the phlogiston's chaos. I'm not sure where phlogiston comes from, unless it's a compound of ethereal and astral matter that can't exist within a sphere or on any other plane.

If you believe the creation myth in Hellbound: The Blood War, Evil, Good, Law, and Chaos (and possibly Balance as a fifth) all emerged at about the same time, approximately simultaneously. First of all these concepts existed on their own; tiring of warring directly, they created progenitor races (including the baernaloths, and I'd tentatively identify the other progenitors as the true slaadi, the kamerel, the priminals, and the Twin Serpents), who in turn created the first planar races (including the yugoloths, guardinals, slaadi, and so on).

I think if either axis originated first, it would be the Law-Chaos one, since that doesn't require sentience. Fiendish Codex II suggests that Law and Chaos warred long before anyone knew what Good or Evil were, but that's just presented as a myth, and isn't to be trusted.

I would argue that the Astral is not belief and memory personified, but is actually a non-space between the planes in which belief and memory were able to collect. While time does not pass in the Astral, it can only exist within time.

Yes, the yugoloths must have already existed, but their equivalents among the hosts of law and chaos probably came into being at about the same time. I did suggest that yugoloths were older than obyriths, based on the idea that the obyriths (rather than the later tanar'ri, as Faces of Evil had said) were what the General of Gehenna created when he cast the chaotic larvae from the yugoloth race. However, I think there were probably chaotic outer planar beings in existence before the obyriths - I think the slaadi were probably older, for example. And I think the aphanacts preceded the elder Baatorians.

It's clear that the concept of good must have existed, then, by the time of the Battle of Pesh. I think Chan and Sunnis's innovation wasn't to become aware of Law, but simply to make an alliance with it.

I wouldn't. It's easy to imagine nonliving matter is an organized or disorganized state. It's harder to imagine it having morality.

Have you ever looked at ants and other social insects? They're definitely organized, and their organization has nothing to do with physical force or might. How about bonobos, which rely on socialization rather than intimidation? Do ducks fly in formation purely because they're intimidated by the might of the alpha duck? They do not; they have an instinctive sense of order. How about symbiotic relationships between species, or the way the vast complex systems in a single organism work together in harmony (probably evolving from multiple symbiotic organisms working together in ancient times)?

Besides which, complaining about order doesn't make it less orderly. Tanar'ri don't have the smooth harmony of a wolf pack hunting in concert; they're a mob of individuals who war against one another even as they attack those they feel mutual hatred for. Wolves, once they've established the pecking order, cooperate with an elegance that can only be called orderly. The criteria they use for choosing their order doesn't make it disorderly; even baatezu generally appoint the mightiest among them to be their leaders.

Cats, now. They're a chaotic species if ever there was one. Even if one establishes dominance, they still don't cooperate (lions excepted). But canines are lawful.

Well, I understand the resolution to this problem when it comes to differing views of personal values, which is what separates the various outer planes. It becomes more difficult to explain when you are talking about competing views of the factual state of reality, which your explanation only somewhat addresses. I realize the suggestion is that basically given any competing view of reality, you would expect a plane of existence to spring up to accommodate that view if given sufficient belief (presumably an awful lot, which means it would have to reflect pretty fundamental and/or primal ideas like good and evil). But if you consider that one's belief about the factual state of affairs is entirely personal and based upon your own knowledge and experience, with random overlap with various other people, wouldn't that result in a bunch of demi-planes to accommodate various beliefs, or at least an infinite expanse of transition between particular beliefs rather than hard planar boundaries? Certain places like the outlands sort of serve that function, but ideologically each plane is fairly distinct and there is generally little suggestion of gradient other than the gatetowns, and the gatetowns themselves provide a pretty definitive ideological boundary (I might be persuaded otherwise on that point, as there are some other places where such gradients are suggested, just not as commonly as might otherwise be concluded).

I think the "inertia" idea suggested by NichG (that established realities are very difficult to undo, especially when it comes to certain fundamental rules) is a good partial solution. The infinite possible realities of which any given person occupies one is another good way of getting around the problem because it basically says the irreconcilable situations create parallel dimensions.

Now, the suggestion that new planes (or new parts of existing planes) are just shapes to accommodate competing beliefs seems reasonable enough as a way to resolve things, but then you have to wonder why belief would do anything other than shape otherwise unshaped parts of the multiverse (and why not since the multiverse is infinite?). It would seem sort of contrary to that idea to then say belief can affect pre-existing areas, since it seems to resolve conflict not by choosing one idea over another, but rather by simply taking the path of least resistance and shaping some unshaped area to meet the particular belief. It makes sense that an area might grow the more new belief reinforces the idea, but it is hard to see why belief would be changing areas already established when the path of least resistance would seem to be working with the raw potential of the ethereal, or working with whatever it is that allows belief to shape infinite planar expanses. If the planes were limited in size, then you might have a justification for belief changing pre-existing areas previously shaped. To use an analogy, a lake filled to a certain level might break the banks and flood the valley below. But why would that lake do anything but keep filling up if its basin was of infinite depth? Maybe there is an underlying geography to the planes that directs this belief like the contours of a valley, a geography that has no bearing on the actual physical makeup of the planes? Such an idea though would almost require a new coterminous plane to explain such a thing.

Which leads me back to the apple thing. My point was that there is plenty of reason to have a particular view about the factual state of affairs (such as the number of apples on a table), even though you are often liable to be wrong. After all you can't constantly be aware of every factual change in the multiverse. So it would seem to me that, given the vast possibility for wide variation in views on every day things, the tendency of the multiverse would be towards the average (or possibly modal) explanation, which would make change in that state very difficult, because any change would inherently be contrary to the common average belief, especially since the reality in place initially must conform to that average belief. I sort of get the impression that you are saying that belief really wouldn't impact explicitly factual things at all, and at best might shape stuff in some distant part of an outer plane, but I think for that to be valid you almost have to reject the possibility of change in factual states of affairs via belief, which would have vast repercussions.

Sure. But these are mathematical attempts to explain a property we observe, but there is no such thing as the perfect roundness or ideal redness we can conceive of. We can describe it, but it doesn't exist, partly because the idea is something apart entirely from the reality of the thing the idea derives from. Redness is a property of an object that exists in various degrees, but redness is not a thing in itself. It is an idea that encompasses certain phenomena, but which exists outside the presence of those phenomena in our minds. It would be similarly reductive to treat hate, envy, love and other essentials of the outerplanes to merely the biochemistry that produces them. Redness only exists physically as a property of a thing, specifically light cast off an object. Roundness is a little different in that it is a geometric description to which objects conform to varying degrees, but the issue is fundamentally similar. The wavelength of light is certainly a thing in itself, and it can't be denied that it does certain things in the world (well, it can be denied, but that's a whole different problem), and similarly shapes exist and things conform to various geometries and such objects behave in a certain way. But the experience of these things is also subjective, and our conception of them does not really reflect the reality we face. When we think of redness as an idea or roundness as a shape, our mind is not accurately reflecting our experiences of these things. It does not reflect a particular wavelength or offer up a particular specimen we've experienced that is sort of round. We have a notion of these things that the world somewhat conforms to. Rather we think of abstract objects with idealized properties, or sometimes just a set of rules.

The point is, belief should reflect how we think about things, and thus a realtiy shaped by belief should reflect that sort of thinking. That is contrary to the real world where how we think about things is a reaction to the state of reality. Thus red isn't the way it is because we think it is that way (which would be the Platonic view and seemingly the Planescape view). Obviously you know that, but you don't seem to be address the very serious issue this presents. Basically, if in planescape Redness is a function of wavelengths, that must assume redness was first imagined as being a wavelength rather than a color, since there is nothing in the belief of color that anyone would have that would require wavelengths, and if anything people's beliefs would likely reflect a vastly simpler and less realistic explanation (if you need proof of that, just as 20 people around you how color works). And roundness would first be conceived of as a perfect two dimensional shape rather than a lumpy rock. But the multiverse is filled with lumpy rocks and, apparently by your own admission, wavelengths of light that are perceived as color. Unless those things are preconditional physics of the multiverse, why would that be how things manifest themselves? Shouldn't the outcome of belief conform to the nature of the belief itself? When you get right down to it, if they think color is a certain thing that works in a certain way (which I think you would agree would not likely be wavelengths of light), shouldn't that be how color works?

I guess what I am getting at is that essentially belief, unlike say gravity, does not follow a fixed set of rules. Gravity is essentially a mathematical explanation for a predictable behavior of matter in the universe. Belief does not really have a similarly fixed property, because its effects are widely variant, highly contingent upon the believer, and essentially subjective, so the idea that it produces a fairly stable universe with a fixed set of rules implies that there are lots and lots of things everyone basically agrees upon that just so happen to create conditions similar enough to our own reality. But that requires that people's explanation of physical reality basically matches closely our own scientific understanding of reality, otherwise we would expect very different rules. Things might fall only if they are dropped by someone or something for example, rather than because bodies with mass attract one another. But given the world they live in, their ideas about things should be radically different from what is now our common understanding of how stuff works, color being just one such example.

There are a few different situations in Planescape where reality in the Outer Planes "splits" based on differing points of view. The oldest and most potent division is obviously based on alignments, which define the Outer Planes more than anything else. After that, you'll see different pantheons coming into existence depending on the cosmology of different cultures. That is, one culture might see Thunder and its associated deities in one light, and one culture might see atmospheric phenomena in a different light, and rather than the multiverse generating a single composite thunder god, there's a different thunder god for each culture. These are subordinate, as far as outer planar organization goes, to the alignments, which might have more influence because they're bigger, more universal, or perhaps simply because they've been around longer.

You bring up other basic natural laws, like geometry, color theory, and gravity. It's true that different cultures organize colors in different ways (the Chinese recognize yellow-orange as a color, but not yellow; there are African cultures that count blue and black as the same color), but it's not immediately clear to me how this would effect the planes or the laws of nature. Insofar as there are gods for these things, each culture has its own.

In situations where the perception of things is truly individual (in color perception, for example), it's easy to imagine each person's belief affecting only themselves. In your thought-experiment with a multiverse containing only six people, if each person has their own opinion on what color something is, that person can continue to have their own opinion without that belief affecting anyone else's. The object simply exists in a subjective, "quantum" state without any "true" nature that can be divined. And I'd say this remains true even if five of our lonely souls see something as purple and one insists it's a vivid neon green. When one's perception affects only oneself, there's no reason to assume reality would be democratically imposed.

In the Outer Planes, more likely a bunch of realms. But everyone doesn't need their own realm; as above, it's really only a situation where one's opinion matters, as in a great philosophical movement or religion. So I don't think there needs to be a region in the Outer Planes where everyone thinks spaghetti is awesome slowly fading into a region in which people think spaghetti is merely adequate.

It's also true that most beliefs don't map precisely onto the outer planar landscape because the alignments have such overwhelming priority. So, for example, the Egyptian pantheon is scattered throughout the planes rather than having a single massive realm representing the Egyptian cosmological view, overlapping with neighboring cultures like ancient Kush or Assyria. The conflict between Law, Chaos, and other greater forces has broken that up. The same is often true of any philosophical viewpoint, which usually fail to shape the planar landscape significantly (which is why the Sign of One and Doomguard don't have their own planar realms).

Just about any cohesive philosophy makes for a great idea for an outer planar town, however, and this town can be pulled into one plane or another depending on the influence of Law, Chaos, Good, or Evil inside it.

The Outlands grow more chaotic toward aoXs and more harmonious toward Fortitude, and more wasted toward Hopeless and so on. Closer to the Spire, though, everything becomes more balanced.

I think there's some truth to that. Another thing to keep in mind is basically what I've been saying for some time in this thread: that Planescape doesn't really present a multiverse where everything is generated by belief, just one in which belief is very powerful and influential, especially in the Outer Planes.

I think the answer is that there's a distinction between changing existing beliefs and coming up with entirely new beliefs. Law and Chaos are entirely different beliefs and they can't really change each other, only affect what influence each has on other things. So there are separate planes of Law and Chaos, and an individual town or realm can be pulled toward one or the other. In influencing where a town slides, you're shaping existing beliefs (the existing beliefs of that town's inhabitants and, perhaps, the philosophy that town personifies) rather than creating a completely new philosophy/town that would probably appear in some unshaped part of the Outer Planes, independent of any existing one.

In our hypothetical universe of six, if three people thought that libertarianism was good and three people thought it was evil, the town of Libertarianburg would probably end up somewhere in that universe's equivalent of the Outlands.

This geography is defined, to a very large extent, by the larger aligned forces. To a lesser extent, powerful pantheons define planar geography. Other than that, the outer planes have no "actual physical makeup." It's all reified belief.

Perhaps. For the most part, I don't think belief affects everyday things at all, if only because people rarely have strongly divergent opinions on them. In your apples example, my first instinct was to say the average number, four, would win, but I remembered that there's more than one outer plane, and there's a reason for that.

I think the main repercussion is that you'll end up with a Planescape that looks like the published Planescape. As you pointed out earlier, if people believe that anything enough people believe becomes real, why wouldn't they concentrate on dreaming up the best of all possible worlds? The Dustmen believe everyone is dead not because they desperately want this to be the case (although there might be some of that), but because they're convinced it is the case, and that it will always be the case regardless of what anyone thinks. And outside the Outer Planes, the idea that belief is power is much less common.

So if belief does affect the fundamental nature of reality, most people don't seem to believe it does. Which is a paradox.

I think colors might actually be things in themselves on the Quasielemental Plane of Radiance. If there are Platonic shapes, they probably exist on Mechanus (and, in "fallen" form, in Acheron; in "ideal" form in Arcadia, and I'm not exactly sure how an idealized shape might be different from a Platonic shape - maybe the corners aren't as sharp). On more chaotic planes, people would be more dubious that shapes are Platonic things and not just imperfect, subjective descriptions of things (and I have a long-delayed reply to Idran on that subject).

Emotions, for their part, seem most real and affecting in Arborea and the Abyss, which seem for whatever reason to personify them. It's likely that in less chaotic planes, emotions are thought of as less objective.

In Planescape, redness is probably a primal schism in the pure light of positive energy, and probably precedes any belief in what redness might be. I'm not convinced that redness is something that can be affected significantly by belief, with the Plane of Radiance continually reminding the multiverse of what redness really is.

The same probably applies to most everyday things, with reality being defined in the Inner Planes and interpreted elsewhere. The symbolic associations of red might be found in the Outer Planes (for example, in red slaadi and red abishai), but I think Planescape does present a "pre-existent reality" that isn't defined (at least, not primarily) or generated by the vagueries of what people believe them to be.

On this argument, I might direct people to a good book called "Godel, Escher & Bach". It's a dense read but I found it informative.

In the work, they touch upon Godel's Incompleteness Theorems. In HEAVILY simplified form, Godel created a mathmatical paradox that exposes that all mathematics have underlying asumptions. If these implied assumptions are true, then the rest of mathematics holds true but if the assumptions aren't true, then the rest falls apart.

In an area where this might be more obvious, look at Euclidean geometry. There are five basic postulates that are "obvious" but can't be proven. These include things like "Two parallel lines can never cross" (actually this one is derived, but it isn’t written in the esoteric language of the real postulates)
Thus geometry was born and chugged along happily for centuries.

However, along can Einstien with his theories that space can be curved. Suddenly, the postulates that Euclid used as a foundation might not be valid anymore. Near a black hole (let’s say) it might be possible for parallel lines to intersect.
Now we have a whole field of mathematics devoted to non-Euclidean geometry where they build up a set of new rules when they consider one or more of Euclid’s postulates to be tweaked in some way.

While it’s hard to imagine (at least I can’t) a situation where 1+2 <> 3 or where 1+2 <> 2 +1 (neither of which can be "proved"); it doesn’t mean it’s impossible (just improbable) that people would conceptualize something outside the norm.

And given Xaositects love of freedom/chaos; I could see them trying to interpret all of existence in new ways and throwing out the "obvious" rules of being out the window in an effort to find something new.