Early sources citing distinguishing dreams do so in four types. Dreams from a physical indisposition, prescient dreams, dreams connecting the supernatural with humanity, and dreams coming from thoughts. Dreams are modernly revered as being capable of foresight. The Buddhist Treatise on Transcendent Wisdom goes on to classify dreams into five kinds if there is fever, one will often dream of fire, seeing yellow or red. If there are chills, then one dreams of water, seeing white. If there is palsy, one dreams of flying, seeing black. Things one experienced appear in dreams or thoughts protruding in the mind. Celestial beings are those involved in dreams to inform people of future events. It has been said that the basic nature of the existence of the universe on a higher level is evident through dream interpretation. Dreams can also be divided into passive dreams and active dreams. Passive dreams being individual expressions of people's subconscious, or manifestation of external influences. Dreams are not the results of sheer will but external forces. Forces that science has yet to discover. Another type of classification or dream interpretation originates in ancient Chinese theories of dreams. Mostly, based on the illustration of dream by the psychological state of the dreamer. In this type of study dreams can be divided into six types. One being accurate dreams, second startling dreams, third being thoughtful dreams, fourth insightful or awakening dreams, fifth joyful dreams, and sixth nightmares. Another interpreter Wang Fu goes on to say that, "Ten elements are the general parameters of dream interpretation." He also classifies dreams into those that have validity and those without validity. However, he also says, "Extraordinary dreams mostly have a reason; few are meaningless." Dreams may be direct, or they may be symbolic; they may involve vitality, thought, personality, feelings, or the times. In them may be reversal, sickness, or sexuality."