that there were different fractions of qi—the coarsest and heaviest fractions formed solids, lighter fractions formed liquids, and the most ethereal fractions were the "lifebreath" that animated living beings. Yuanqi is a notion of innate or prenatal qi which is distinguished from acquired qi that a person may develop over their lifetime. Philosophical roots The earliest texts that speak of qi give some indications of how the concept developed. In the Analects of Confucius, qi could mean "breath". Combining it with the Chinese word for blood (making 血氣, xue–qi, blood and breath), the concept could be used to account for motivational characteristics: The philosopher Mozi used the word qi to refer to noxious vapors that would eventually arise from a corpse were it not buried at a sufficient depth. He reported that early civilized humans learned how to live in houses to protect their qi from the moisture that troubled them when they lived in caves. He also associated maintaining one's qi with providing oneself with adequate nutrition. In regard to another kind of qi, he recorded how some people performed a kind of prognostication by observing qi (clouds) in the sky. Mencius described a kind of qi that might be characterized as an individual's vital energies. This qi was necessary to activity and it could be controlled by a well-integrated willpower. When properly nurtured, this qi was said to be capable of extending beyond the human body to reach throughout the universe. It could also be augmented by means of careful exercise of one's moral capacities. On the other hand, the qi of an individual could be degraded by adverse external forces that succeed in operating on that individual. Living things were not the only things believed to have qi. Zhuangzi indicated that wind is the qi of the Earth. Moreover, cosmic yin and yang "are the greatest of qi. He described qi as "issuing forth" and creating profound effects. He also said "Human beings are born [because of] the accumulation of qi. When it accumulates there is life. When it dissipates there is death... There is one qi that connects and pervades everything in the world." The Guanzi essay Neiye (Inward Training) is the oldest received writing on the subject of the cultivation of vapor [qi] and meditation techniques. The essay was probably composed at the Jixia Academy in Qi in the late fourth century B.C. Xun Zi,