Dream energy
Dream energy is the still poorly understood quantity that fuels dream magic. Despite the common name, it isn't really a form of energy, in the physical sense, but is more a sort of magical potential—and in fact is sometimes called "dream potential", though that name, though more accurate, is less commonly used than "dream energy".
Creatures in the cosmos of Ses gather dream energy when they sleep, during which, according to the most accepted theories, they somehow mentally or spiritually enter another cosmos, known as Goetogenia. On waking, they can use this energy to cast spells and perform other acts of magic, or their magical energy can be siphoned off and used by others.
Rate of accumulation
Some people seem to inherently accumulate dream energy more quickly and readily than others, but its acquisition is also a skill that can be developed over time, with people learning with training and experience to dream more "efficiently" and gather energy more rapidly. Some scholars have tried to find links between the untrained rate of accumulation of dream energy and other traits such as intelligence and physical strength, but no such correlations have been proven; at best, there may be some very weak correlation with creativity or with self-awareness, but the grounds for this are shaky, the more so given the ill-defined nature of the qualities in question.
Exactly why some people gather more dream energy than others, regardless of whether the difference is innate or learned, is also poorly understood; it's not clear whether those who gather dream energy rapidly are somehow dreaming differently than those who gather it more slowly. Some scholars hold that the difference results from the dreamers' visiting different parts of Goetogenia, some of which are more richly endowed with dream energy than others. The fact that dreamers with different energy accumulation rates have encountered each other in their dreams, however, casts considerable doubt on this idea. Others opine that the different rates of energy accumulation stem from the dreamers' activities while dreaming; perhaps the more power he gains in the dreaming world, for instance, the more magical potential he bears on waking. A comparison of the dreamlives of fast and slow dreamers, however, has found no consistent and compelling differences. Another theory is that it is nothing about the dreams that affects the rate of dreaming, but something about the dreamer, that some feature of the dreamer's mind, body, or soul changes to allow him to more efficiently absorb dream energy. No more evidence has been found to support this theory than the others, however, and the matter remains in dispute.
Spellcasting
The best known use of dream energy is to use it to cast spells. There are a number of different ways of doing this, and in fact whole distinct techniques of manipulating dream potential into spells have arisen, leading celemologists to classify all spells according to a system of carminical taxonomy according to the details of their development.
Some people cast spells unconsciously in their sleep, often using it up as quickly as it accumulates. Depending on the particular spells being cast, such sleepcasting can be dangerous.
Siphoning
Some wizards, not content with the dream energy they gather themselves in dreams, develop the ability to use the dream energy of others—perhaps without their consent, in a process known as siphoning. A person whose dream energy is being siphoned off by another wizard is known as a dreamthrall of the wizard doing the siphoning, though that term shouldn't be understood to imply that he is necessarily under that wizard's compulsion in any other way; if the dreamthrall is not himself a spellcaster, he may be completely unaware of the uses to which his dream energy is being put. Siphoning has reached particular heights on the world of Dadauar, where powerful mages called onirarchs have the dream energy of entire populous nations at their disposal.
Ambient magic
In light of the fact that dream energy is gathered in dreams, the fact that some objects and beings use magic without dreaming requires explanation. Talismans with finite uses, such as s, are easily explicable as having been endowed at their creation with some quantity of dream energy that is expended at their use, but those with repeated or continuous effects seem to require access to an unlimited source of dream energy the origin of which is not obvious if they're not being fueled by a living and dreaming creature. The spontaneous enchantment of certain natural features raises similar issues, perhaps more so. Certain magic-using living, or unliving, entities also pose something of an enigma; undead, for instance, do not dream, but may be quite capable of spellcasting. In the last case, there is some evidence that even unsleeping creatures do somehow dream with a part of their minds, subconsciously visiting Goetogenia while awake. Some celemologists have tried to extend this explanation to nonliving objects, positing that anything with a magical enchantment does have a life of some sort and does dream, but many find this hard to swallow; the idea that a lowly potion or enchanted dagger is in some sense alive may not be readily disprovable, but strikes most scholars as unlikely.
The preferred explanation is that there exists some form of ambient magic, environmental dream potential that talismans can draw upon for these effects. The source of this ambient magic, however, has not been proven. The prevailing theory is that it simply represents unused dream energy, that the dream potential gathered but never used for spellcasting or other effects eventually bleeds off into the atmosphere. In principle, this could perhaps be tested; if all the dream energy in a given area were used for spells, the theory predicts that talismans brought in the area would cease working. In practice, this would be infeasible to arrange, and in any case the failure of such an experiment still wouldn't definitively settle the matter, since the necessary range is unknown; it could be that ambient magic acts at great distances, and that talismans could be adequately powered by leaked-off dream energy on distant worlds—most celemologists consider this unlikely, but it remains a possibility.
Other theories as to the source of ambient magic exist, but are considerably less popular. Some believe that Goetogenia and Ses are one and the same, that dreamers visit not another cosmos but only another part of their own, and that the dream energy inherently exists everywhere in the cosmos but must be processed through dreams for use in spellcasting—but can power talismans and other nonliving effects in its raw form. This theory, however, while never very widespread to begin with, has recently been dwindling even further in popularity. Others believe that ambient magic is produced by the dreams of the gods, or by the spirits of the dead. Another theory is that dream energy has another route into Ses other than by dreams, though there are conflicting ideas as to what that route is. An interesting theory that remains on the fringe but is gaining some ground is that ambient magical effects are powered by the dreams of some yet unidentified beings called "facilitators".