JEET KUNE DO contains a definite structure and specific principles that have guided its development. As Lee examined different martial arts, he used these principles to evaluate whether or not a particular technique should be included in the art. A technique had to fit into the existing structure and work efficiently with other techniques in order to be included.

The maxim “Absorb what is useful, reject what is useless, and add what is specifically your own,” characterizes the “research” and “experimental” aspects of Jeet Kune Do. In his research Lee tried to identify techniques that could enhance his fighting style and to understand how other stylists fought so that he could develop ways to counter them. He critically read thousands of books on judo, boxing, wrestling, fencing, and other arts, often underlining the text and making notes in the margins when a particular idea struck him as significant. Lee also attended demonstrations and martial arts tournaments, carefully watching participants in order to understand the essence of their style. He sought out and trained with martial artists from many disciplines so that he could learn from them.

Lee concluded that kata, or forms, had limited usefulness because they bore little resemblance to real combat. Recognizing that fights did not fall into established patterns, he regarded these exercises as “swimming on dry land.” Lee believed that to become an effective fighter, one had to actually swim in the water, which meant sparring.

Lee also came to understand that, in order to adapt to the changing dynamics of a real fight, a person had to develop skill in combat at any range. He realized, for example, that Wing Chun worked best at close range, but that other methods were needed, for both close range and other distances. Therefore, Lee incorporated kicking techniques from other gung fu systems, as well as Savate, for intermediate-range fighting. He also took punching techniques from Western boxing for intermediate range. Finally, he added chokes, strangleholds, locks, throws, and takedowns for close range.

Lee concluded that it was important to aggressively close in on an opponent, rather than passively wait for an opponent to approach. Further, it was better to avoid being hit than to block an attack. Thus, Lee drew on fencing and Western boxing because their superior footwork and mobility allowed him to quickly bridge the gap when attacking and to quickly evade when being attacked.

Many of the principles of Jeet Kune Do were borrowed from Western fencing. These include broken rhythm, interception, and simple and direct movements. Indeed, Lee’s art has been characterized as “fencing without a foil.”

Many martial arts systems that Lee examined were of the “block and hit” variety. When a person was attacked, that person would block the strike and follow up with a strike. Through fencing, Lee found a more efficient way to deal with an attack. A good fencer would not merely block or parry an attack but would strike as an opponent prepared to attack, thus intercepting the attack. Lee applied this principle to empty-handed fighting, meaning that a person could intercept with a punch or kick as the opponent started to attack.

Lee realized that no single martial arts system had all the answers to every situation. Thus, to stick to one particular “way” of fighting, as he called it, was to cling to “partiality.” Rather than be bound to any particular style, Lee strove for “totality” in fighting, using any method that worked, no matter what its source. He believed that individuals should train their “tools” (the parts of the body used for fighting) for maximum effectiveness, according to their own abilities, and that this training was more important than any style. Individuals should experience “freedom of expression” in fighting, so that they can act in response to reality, rather than to a preconceived notion of what a fight “should” be like.

Lee’s extensive research led to the following principles, which guided the development of his art:

Generally speaking, Lee did not see value in the practice of gung fu forms and karate katas, because they did not match actual fighting situations. The exceptions were the sil lum tao from Wing Chun and a kicking set that he had developed.