Fundamental to the law of dependent origination are the seals (or marks) of the Law. Seal is used in the sense of a brand that guarantees the validity of a document and serves as a person’s mark. Thus the seals of the Law are simultaneously its characteristics and its proof. Any theory that conforms to these characteristics is true; any theory that fails to do so is false. The three seals state that all things are impermanent, nothing has a persisting self, and nirvana is tranquility. Sometimes a fourth, all existence is suffering, is added to make the four seals of the Law.