Imitative Magic is sort of a sub-category and sort of core foundation of sympathetic magic. It is based on the idea that an object can manipulated by another similar object. An expert sympath can form a connection between a poppet and a person, and inflict harm on the individual by harming the doll, which is the basis of Voodoo. This even extends between realms, such as the mirror realm and the physical realm. It also explains why damage done to buildings in the Spirit World will be reflected in the physical realm over time. However there is a weakness to the technique when used from the mirror realm. Since the items in the physical world have more "weight" then if the items used are move then the reflections react in the same way.
Contagious Magic is a sub-category of sympathy. It is based on the idea that after having contact once, an object will always remain in contact even after they have been separated. An example in story would be when Conquest attempted to possess Rose's hair and, by contagion, Rose herself.