There are three kinds of Power that have been created as the foundations of Realms and to push back the Entropy of Chaos. First there was Logrus - defined amongst academics as a 'Constraining of Chaos'. Second there was Pattern defined as an 'Imposition of Order'. In effect, both these Powers result in the same things - a material Realm and an origin point for Shadow. But the nature of the realm and the ability of the initiates of the Power are polar opposites.
More recently a third kind of Power has been created, referred to as a Neutral Power. In effect, this is a Power which, either by accident or design, has elements of both the Constraining of Chaos and the Imposition of Order. Neutral Powers do not take completely opposite relationships with either Pattern or Logrus. However, by quirk of fate, they do all become polar opposites of other neutrals.
The first Neutral to be made was the Twister, created by Kelric. All stories indicate that he was attempting to draw a Pattern, but he was disturbed during the process by an attack of Abyss Hags, and the Creation went wrong.
The second Neutral was created by Corwin - while again attempting to Create a Pattern, it is clear that he either had not studied sufficiently, or attempted to change too many things as he went, such that he also ended up creating something that is not a Pattern.