Magical laws of Opposites are the laws that govern how opposing spells interact with each other. There are several such laws that are known, and likely still more to be uncovered.
Background[]
In general, the laws of Opposites allow a wizard to manipulate one form of energy, matter, or simile in order to achieve its apparent opposite. An example might be the death of a sacrificial being in the attempt to create life in another. Another might be the endless removal of portion upon portion of a single cake in order to feed sweet treats to multitudes; in consuming the cake, more is created.
Another form of the laws of Opposites concerns the idea that for every magical spelling, conjuration, or ensorcellement, there exists a negating incantation or enchanting; an opposite that is used to cancel, or oppose the first. Rainmaker is an excellent example of this kind of magical law of Opposites. Because it cleanses the air, it can be used to nullify smoke spells or enchantments of psychic befuddlement and depression. It goes without saying that it opposes many of the fire magics most effectively.[1]
The magical laws of Opposites is probably related to the additional law; that any spell, no matter how powerful, could always be removed by another magician of sufficient skill.[2]
All spells always have a weakness somewhere.[3]
Behind the scenes[]
The reference to feeding cakes to multitudes, is a reference to the story of Jesus feeding multitudes with only five loaves and two fishes.
The never ending 'Chest of Gold' seems to operate on this principle, as does the Fairy wallet.