Japanese martial arts refers to the enormous variety of martial arts native to Japan. At least three Japanese terms are often used interchangeably with the English phrase “Japanese martial arts”: “budō” (武道?), literally meaning “martial way”, “bujutsu” (武術?), which has no perfect translation but means something like science, art, or craft of war, and “bugei” (武芸?), literally meaning “martial art.” The term “budō” is a modern one, and is normally intended to indicate the practice of martial arts as a way of life, and encompassing physical, spiritual, and moral dimensions with a focus of self-improvement, fulfillment, or personal growth. The terms bujutsu and bugei have more discrete definitions, at least historically speaking. Bujutsu refers specifically to the practical application of martial tactics and techniques in actual combat. Bugei refers to the adaptation or refinement of those tactics and techniques to facilitate systematic instruction and dissemination within a formal learning environment.
Hard and soft methods
There are two underlying strategic methodologies to the application of force in Japanese martial arts. One is the hard method (剛法, gōhō?), and the other is the soft method (柔法, jūhō?). Implicit in these concepts is their separate but equal and interrelated nature, in keeping with their philosophical relationship to the Chinese principles of yin and yang (Jap.: in and yō).
The hard method is characterized by the direct application of counter-force to an opposing force. In practice, this may be a direct attack, consisting of movement directly towards the opponent, coinciding with a strike towards the opponent. A defensive technique where the defender stands their ground to block or parry (directly opposing the attack by stopping it or knocking it aside) would be an example of a hard method of defense. Hard method techniques are generally conceptualized as being linear.
The soft method is characterized by the indirect application of force, which either avoids or redirects the opposing force. For example, receiving an attack by slipping past it, followed by adding force to the attacker’s limb for the purpose of unbalancing an attacker is an example of soft method. Soft method techniques are generally conceptualized as being circular.
These definitions give rise to the often illusory distinction between “hard-style” and “soft-style” martial arts. In truth, most styles technically practice both, regardless of their internal nomenclature. Analyzing the difference in accordance with yin and yang principles, philosophers would assert that the absence of either one would render the practitioner’s skills unbalanced or deficient, as yin and yang alone are each only half of a whole.
Source and References http://en.wikipedia.org/wiki/Japanese_martial_arts