Sympathetic magic, sometimes called symbolic or imitative magic, is spell work that is done with something that looks like your desired outcome. This type of magic is based on the belief that you can create a “map” or example of what you want to happen and then push energy in the direction of your desire. This is based in part on the theory of contagious magic which is the belief that a person’s body parts carry their essence, and that if you aren’t careful with your hair, blood and other body parts (this includes menstrual blood and other discharges) that another person can take these items and create an effigy of you to do spell work on your behalf. It is the binding or linking (sometimes called a tag lock) between two things.
Examples of sympathetic magic include voodou work with poppets, the use of animal skins to transfer power to a warrior, or wearing feathers, bones, amber or other stones.
Sympathy is the ability to put yourself in the place of another person and feel their emotions, or to manipulate energy toward a desired outcome. When you create a doll/poppet, you put your knowledge of a particular person into the doll. You can add an item belonging to that person (fingernail clippings, blood, etc.) to attach the doll to the person the spell is intended for. You then can add other symbolic items inside the doll to power the spell such as a heart. Once the doll is created, you can use it to send the spell you desire to the recipient. It should be noted that voodoo dolls are used for healing spells more often than spells of hate or revenge.
Sympathetic magic is also used in working with correspondences, or the use of mundane items in your magical work. Examples of correspondences include the use of red candles in love spells or rose quartz to help heal emotions. The colors or items themselves don’t carry magical properties, but your belief that using them is the correct process carries the weight of your intentions. This is why you use red thread in many different types of spell work.
More information on voodoo, hoodoo, root work and other folk traditions can be found in books at your local metaphysical bookstore. One of my favorites is “The Magic of Marie Laveau: Embracing the Spiritual Legacy of the Voodoo Queen of New Orleans” by Denise Alvarado.