Ki is possibly the most powerful, useful and even quintessentially Japanese word in the Japanese language. Familiar to everyone from fans of modern manga to practitioners of ancient Aikido, alone or in combination with other syllables, ki can mean many things.

Among the words and concepts incorporating that one sound are the words for feelings (kibun), weather (ten ki), energy (genki), gloom (kiomo), and on to the words for heart, mind, spirit, flavor, spark, value, humor, scent, interest, essence, energy, atmosphere, will, intention…even tree. The list is long. And when combined with other words, ki can create phrases of great nuance and versatility: ki ni iru means to like something; ki ga kawaru means to change one’s mind; ki ni kakeru evokes the notion of worry.

Uniting all those various words is a sense, though hard to pin down in other languages, of change, of something moving within the spirit or emotions of a person, a place…even a thing. The problem of assigning any clear, unambiguous definition of ki is obvious: Ki is ephemeral, ambiguous. In fact, the difficulty comes because that ambiguity is a part of ki itself.

As with many notions in Japanese, the meaning of ki is accessible on basic, quotidian levels – tree, remember? – but the more one looks into it, it takes on deeper and broader levels of refinement and subtlety. Given this, it is essential to start on the simplest level.

Perhaps the most important of the many meanings of ki is what is often translated as spirit, or energy. It is this sense that we can focus on to begin, for it is the meaning of the word that brought the concept to Japan more than a millennium ago.


Brought from China with Buddhism in the sixth and seventh centuries C.E., the Chinese word chi (or qi) is familiar to many, even in the West. In writing the word, the Japanese still use the Chinese character, or kanji, for what is pronounced chi. That pictogram, 気, combines the symbols for rice and steam or vapor, combining a simple “inanimate” thing with an animation that brings it alive, as some sort of energy is released.

At the same time, this ethereal notion is grounded in the simplest, most day-to-day process, of cooked rice doing it’s most basic function: releasing energy, in the form of heat and vapor.

But the meanings of chi and its descendent ki are different. While the Chinese use chi to describe the life force that animates everything – which makes it casually comparable to words used around the world, prana in Hindu, ruach in Hebrew, spirit and its Romantic variations in the West – the Japanese use of the word is far more subtle, ambiguous, and thus, much more widely useful.

Aikido teacher and theoretician Stefan Stenudd refers to ki as “the ether of intention,” and others have equated it with creative flow and inspiration.

Ki’s function in life is well understood in the martial art Aikido, the actions of which are focused almost entirely on the flow of ki. Thus, an attack in Aikido is less about the body of the attacker than about the flow of energy he has initiated, and “ridden.” Consequently, the person being attacked is inclined to use evasive moves to get out of the direction of the attacker’s ki flow.


‏The Aikido master Koichi Tohei wrote, in his 1962 book What Is Aikido?: “What is the light meaning of ki used in our daily life? A good feeling, a bad feeling, a great feeling, timidity, vigor, courage, a retiring disposition, et cetera – these are terms used in our daily life. In each word or phrase, the Japanese use ki as an integral part. The reason is that a human being was created from ki of the universe. While he receives ki, he is alive. Deprive him of ki and he dies; he loses his human shape. So long as his body is filled with ki and pours forth abundantly, he is vigorous and filled with courage. On the contrary, when his body has run out of ki, he is weak, cowardly and retiring. In Aikido training, we make every effort to learn to fill our body with ki and use it powerfully. Therefore, we must understand well the deep meaning of ki.”

‏But ordinary Japanese do not perhaps put nearly as much importance on defining ki that outsiders do. Its meaning is so basic, so woven into the language, into daily life, that few give it a second thought. Ki is just that: ki. A small word that expresses a concept that can be as deep, or as ephemeral, as any given moment.