Humans seem to naturally generate a series of concepts known as sympathetic magic, a host of theories and practices which have certain principles in common, two of which are of overriding importance: the Law of Contagion holds that two things which have interacted, or were once part of a single entity, retain their connection and can exert influence over each other; the Law of Similarity holds that things which are similar or treated the same establish a connection and can affect each other.