"Life force" is probably best known definition of Qi which has its foundation in traditional Chinese medicine and philosophy and it is very important part of Chinese culture . While Qi as a "life force" is understandable for Chinese there is a problem to define it in English or other western languages . The problem is not purely linguistic but rather based in cultural and philosophical differences . There are several definitions of Qi including "material force" ,psycho-physiological power associated with blood and breath" , 'vital force" or "impulse of life" . All these definitions are partially correct but non of them even together cover a full meaning of Qi . This simple example shows how different is eastern way of thinking and perceiving realty from the western way of thinking . While there is a clear distinction between energy and matter , mind and body, physical and metaphysical in western philosophy and languages , such distinctions are far less concentrated on the east . Problem in definition of Qi is that Qi is not energy nor matter but rather both . It is some form of bioenergy and it has certain qualities . There are more than 40 different forms of Qi in traditional Chinese medicine . In classical Chinese philosophy Qi is a force of the universe which brings life and existence to everything . Qi is what make things like earth or rocks dense and it is what person's thoughts are made of . It is a same force with different qualities in different things .
Qi as a biomechanical efficiency is something exclusively found in martial arts . Ability to use body with maximum efficiency with minimum effort is called Qi .Qi used in this context is far less complicated to understand than previous one . It is simple matter of knowing a human body and how to use it in order to get maximum power generation and maximal transmission of the force to the target . Qi is a result of proper skeletal alignment which allows to use a human body as integrated unit and to transfer or receive force and proper sequence of muscular contractions and relaxation .Qi viewed in this way is not something separate from the body , an independent force that circulate throughout the body , as it is viewed in the previous "life force" model . It is more like a state of being .Simple fact that this model of Qi can be examined and measured makes it easily understandable to the western mind .
Every time when martial instructor cannot explain something because he either do not knot understand or find is hard to articulate it he will use term"Qi" . I have seen so many times that lack of knowledge and understanding is covered with "Qi" . Sometimes lack of education which leads to inability to verbally explain things is also covered with term "Qi" . There is only one case when "Qi " is used to explain something that cannot be put in words. There are aspects of martial arts that cannot be easily explained- they are subjective feelings , unique and different for every individual