Two of the Eight Principles. When using the Eight Principles to diagnose a patient, a disease is classified as being situated in either the exterior or the interior. A variety of symptoms are used to assess whether a condition is interior or exterior, including signs from the tongue and pulse. An exterior condition is an invasion of external pathogenic factor, and an interior condition is a disharmony of the Zang Fu or an external pathogenic factor that has invaded the deep levels of the body.