Laws Of Magic: The Law Of Similarity

The Law of Similarity

Like the magical Law of Contagion, The Law of Similarity governs Sympathetic Magic. This law states that a Magician can produce any effect by simply imitating it. In other words, having a physical or mental representation of a thing facilitates the ability to have control or influence over said thing. 
This law supports magical workings like voodoo dolls, poppets, figure candles, and all other spells that involve assigning representation to an object to effect the thing/person it represents.

Benefits:
From the law of similarity has evolved The Doctrine of Signatures, which is the belief that certain herbs and plants govern and have the ability to heal the parts of the body that they similarly represent. For example: walnuts have the ability to strengthen the brain, plants with yellow sap can cure jaundice, and so on.
Under this law a Witch can presume control over anything or anyone he/she wishes so long as she can create / find an object that is similar in aesthetic. ​

The aesthetic similarities between walnuts and the human brain are obvious.

Rute Ventura, “Trump Voodoo Box”

Dangers:
The dangers of this law are the same as the benefits. 
As easily as it is for anyone to work beneficial magic on representational objects, it is likewise as easy to perform malicious spells with sympathetic magic using the law of similarity. You may today be performing a social justice spell with a voodoo doll, but tomorrow could be the subject of someone else's curse. This is why protection magic is always a good idea. 
And while some of the observations made using The Doctrine of Signatures has proven to be beneficial and founded in scientific truth, many are not. The law of similarity is a magical law, and as such it only has complete authority over magical things. While magic and science do overlap, they exist independently without contradicting each other*. If a plant contains harmful toxins, it does not cease being poisonous and begin to be beneficial to the part of the human body it resembles. This however does not necessarily show fault in The Doctrine of Signatures, but could possibly be a result of misinterpretation of the significance of the similarity. 

*More specifically, I believe most forms of magic are not in contradiction with science because magic is a type of science itself - although not fully realized or understood, considered a pseudoscience, and/or not widely accepted to be plausible. It is my opinion that the success of spells is greatly increased with (if not entirely dependent on) the recognition and use of science that exists within magic, and vice versa.