In traditional Chinese culture, qì (also chi or ch'i) is an active principle forming part of any living thing. Qi is frequently translated as life energy, lifeforce, or energy flow. Qi is the central underlying principle in traditional Chinese medicine and martial arts. The literal translation of "qi" is breath, air or gas.
 

Concepts similar to qi can be found in many cultures, for example, Prana in Vedantic philosophy, mana in Hawaiian culture, Lüng in Tibetan Buddhism, and Vital energy or pneuma in Western philosophy. Some elements of qi can be understood in the term energy when used by writers and practitioners of various esoteric forms of spirituality and alternative medicine. Elements of the qi concept can also be found in popular culture, for example The Force in Star Wars. Notions in the west of energeia, élan vital, or vitalism are purported to be similar.

So, what exactly is Qi?
 

Etymology

The etymological explanation for the form of the qi logogram in the traditional form 氣 is “steam (气) rising from rice (米) as it cooks”. The earliest way of writing qi consisted of three wavy lines, used to represent one's breath seen on a cold day. A later version, 气, identical to the present-day simplified character, is a stylized version of those same three lines. For some reason, early writers of Chinese found it desirable to substitute for 气 a cognate character that originally meant to feed other people in a social context such as providing food for guests. 

Appropriately, that character combined the three-line qi character with the character for rice. So 气 plus 米 formed 氣, and that is the traditional character still used today.

Definition

References to concepts analogous to the qi taken to be the life-process or flow of energy that sustains living beings are found in many belief systems, especially in Asia. Philosophical conceptions of qi from the earliest records of Chinese philosophy (5th century BC) correspond to Western notions of humours and the ancient Hindu yogic concept of prana, meaning "life force" in Sanskrit. The earliest description of "force" in the current sense of vital energy is found in the Vedas of ancient India (circa 1500-1000BC), and from the writings of the Chinese philosopher Mencius (4th century BC). Historically, it is the Huangdi Neijing translated as, The Yellow Emperor's Classic of Medicine (circa 2nd century BC) that is credited with first establishing the pathways through which qi circulates in the human body (see also details on Traditional Chinese Medcine (TCM) on this website).

 

Within the framework of Chinese thought, no notion may attain such a degree of abstraction from empirical data as to correspond perfectly to one of our modern universal concepts. Nevertheless, the term qi comes as close as possible to constituting a generic designation equivalent to our word "energy". When Chinese thinkers are unwilling or unable to fix the quality of an energetic phenomenon, the character qi (氣) inevitably flows from their brushes. 
—Manfred Porkert

 

The ancient Chinese described it as "life-force". They believed qi permeated everything and linked their surroundings together. They likened it to the flow of energy around and through the body, forming a cohesive and functioning unit. By understanding its rhythm and flow they believed they could guide exercises and treatments to provide stability and longevity.

Although the concept of qi has been important within many Chinese philosophies, over the centuries the descriptions of qi have varied and have sometimes been in conflict. Until China came into contact with Western scientific and philosophical ideas, they had not categorized all things in terms of matter and energy. Qi and li (理, li, pattern) were 'fundamental' categories similar to matter and energy.

Fairly early on, some Chinese thinkers began to believe that there were different fractions of qi and that the coarsest and heaviest fractions of qi formed solids, lighter fractions formed liquids, and the most ethereal fractions were the "lifebreath" that animates living beings.
 

Yuán qì is a notion of innate or pre-natal qi to distinguish it from acquired qi that a person may develop over the course of their lifetime.

 

Philosophical roots

The [morally] noble man guards himself against three things. When he is young, his xue-qi has not yet stabilized, so he guards himself against sexual passion. When he reaches his prime, his xue-qi is not easily subdued, so he guards himself against combativeness. When he reaches old age, his xue-qi is already depleted, so he guards himself against acquisitiveness.
—Confucius, Analects, 16:7
 

Not only human beings and animals were 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 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."

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 averse external forces that succeed in operating on that individual.
 

Another passage traces life to intercourse between Heaven and Earth: "The highest Yin is the most restrained. The highest Yang is the most exuberant. The restrained comes forth from Heaven. The exuberant issues forth from Earth. The two intertwine and penetrate forming a harmony, and [as a result] things are born."
 

"The Guanzi essay 'Neiye' 內業 (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, another Confucian scholar of the Jixia Academy, followed in later years. At 9:69/127, Xun Zi says, "Fire and water have qi but do not have life. Grasses and trees have life but do not have perceptivity. Fowl and beasts have perceptivity but do not have yi (sense of right and wrong, duty, justice). Men have qi, life, perceptivity, and yi." Chinese people at such an early time had no concept of radiant energy, but they were aware that one can be heated by a campfire from a distance away from the fire. They accounted for this phenomenon by claiming "qi" radiated from fire. At 18:62/122, he too uses "qi" to refer to the vital forces of the body that decline with advanced age.
 

Among the animals, the gibbon and the crane were considered experts in inhaling the qi. The Confucian scholar Dong Zhongshu (ca. 150 BC) wrote in Luxuriant Dew of the Spring and Autumn Annals: "The gibbon resembles a macaque, but he is larger, and his color is black. His forearms being long, he lives eight hundred years, because he is expert in controlling his breathing." ("猿似猴。大而黑。長前臂。所以壽八百。好引氣也。")
 

Later, the syncretic text assembled under the direction of Liu An, the Huai Nan Zi, or "Masters of Huainan", has a passage that presages most of what is given greater detail by the Neo-Confucians:

Heaven (seen here as the ultimate source of all being) falls (duo 墮, i.e., descends into proto-immanence) as the formless. Fleeting, fluttering, penetrating, amorphous it is, and so it is called the Supreme Luminary. The dao begins in the Void Brightening. The Void Brightening produces the universe (yu-zhou ). The universe produces qi. Qi has bounds. The clear, yang [qi] was ethereal and so formed heaven. The heavy, turbid [qi] was congealed and impeded and so formed earth. The conjunction of the clear, yang [qi] was fluid and easy. The conjunction of the heavy, turbid [qi] was strained and difficult. So heaven was formed first and earth was made fast later. The pervading essence (xi-jing) of heaven and earth becomes yin and yang. The concentrated (zhuan) essences of yin and yang become the four seasons. The dispersed (san) essences of the four seasons become the myriad creatures. The hot qi of yang in accumulating produces fire. The essence (jing) of the fire-qi becomes the sun. The cold qi of yin in accumulating produces water. The essence of the water-qi becomes the moon. The essences produced by coitus (yin) of the sun and moon become the stars and celestial markpoints (chen, planets).

—Huai-nan-zi, 3:1a/19

Qi and Feng shui

The traditional Chinese art of geomancy, the placement and arrangement of space called feng shui, is based on calculating the balance of qi, interactions between the five elements, yin and yang and other factors. The retention or dissipation of qi is believed to affect the health, wealth, energy level, luck and many other aspects of the occupants of the space. Attributes of each item in a space affect the flow of qi by slowing it down, redirecting it or accelerating it, which is said to influence the energy level of the occupants.
 

One use for a Luopan is to detect the flow of qi. The quality of qi may rise and fall over time, feng shui with a compass might be considered a form of divination that assesses the quality of the local environment.