Re: define ki
"In the first place, a human being possesses a mind and a body, but these alone are not enough. An activating force is required to connect the mind and the body, and this is the ki in Aikido; it is this that completes the trilogy of ki, mind and body.
Although the founder had a deep interest in philosophy, he probably would not have known of the philosophies of ancient India. However, he appears to have come to the understanding that what he called the 'expert use of ki' is synonymous with that state in which the mind and the body are unified and in harmony with the universe, a state that he achieved through many years of physical and spiritual training. The 'expert use of ki' means making ki work exquisitely and allowing the body to work in harmony with the mind. The founder discovered that the expert use of 'ki' could be realize though subtle changes in breathing."
from a summarized interview with Kisshomaru Ueshiba The Mysterious Power of Ki by Kouzo Kaku pg. 143