Spell Laws

from Ars Magica 3rd Edition, page 195.

When casting a spell, a Magus uses his Gift to manipulate magic in the world around him. For most spells, there are certain vocalizations and gestures that help a Magus control and define this manipulation. There are also certain laws which aid a Magus in his spell casting. These laws are based on observations of how magic works; Magi understand them intuitively without actually vocalizing them. By incorporating the laws into spells, Magi may strengthen Formulaic magic, or even surpass its normal limits.

The Law of Contagion states, quite simply, once together, always together.

Items which were once part of a whole maintain a mystical connection, even when separated. Thus, while Formulaic Hermetic magic is usually restricted by the Range of sight, this limitation may be overcome by having some part of the subject you are trying to affect. For instance, to find a person, you can use a strand of his hair, or a drop of his blood, clippings from his fingernails or even something that is intimate to him, such as clothing or a prized possession. The Inexorable Search is a spell that makes use of these magical laws, and allows Magi to exceed the usual bounds of magic. At the same time, a spell used to instantly return you to your laboratory requires a tile from its floor, or a piece of its wall. The Leap of Homecoming is a spell that lets you exceed the normal Range of Hermetic magic in this way, thanks to a Magus's knowledge of the workings of spell law. Items used to improve magic through the Law of Contagion are known as Arcane Connections.

Another magical law that Magi often use to strengthen their spells is the Law of Sympathy. It declares: that which looks alike is alike. Thus, a representation of someone can aid you if you wish to control her, while starting a small bonfire might help in casting a spell to make a huge one. Quite often, this law of magic is seen in the Spell Focus of a spell, or in the gestures used with a spell.

Spontaneous magic is also affected by these two laws. To gain great Range with a Spontaneous spell, you must have some Arcane Connection to what you are trying to affect. Additionally, you may utilize the Law of Sympathy to strengthen Spontaneous spells, similar to the way Spell Foci strengthen Formulaic spells.

These two laws are present throughout the spells in this book, and should be considered when creating new spells.