Isshinryu karate is occasionally described as a half-hard/half-soft martial art. This is a concept taken from Goju-ryu (go: hard; ju: soft), a forerunner style and extant system of Okinawan karate. Hard or external martial arts are characterized by use of muscular strength, speed, and linear movements. Soft or internal arts (almost always of Chinese origin) are defined by their circular body movements and especially the development of ki or chi. Hard martial arts are explosive, visibly combative and down to earth as it were. The soft or internal arts are ethereal and occasionally fodder for woo-skeptics. In truth, some concept of ju can be found in nearly every system of martial arts. Not meeting force with force, maintaining proper balance and blending with an opponent's energy are methods as worthy as developing as striking power and athleticism.1
In Chinese boxing the contrast between external and internal styles is very well defined. This distinction, however, is somewhat muddled in Okinawan karate.2 "The manner of spitting or drinking is either hard or soft" is taken from the Isshinryu Code (Eight Precepts of the Fist) but few ponder its meaning. In Japanese bujutsu the expression Ju yoku go o sei suru translates as "Softness controls hardness" or "Weakness controls strength."3 This is a philosophy that was probably hijacked from Chinese Daoism. Certainly, proper technique will win over brute strength, as again, this idea is held consistent within all combative styles.
Taking the hard-soft dichotomy to the next level of psychology or philosophy we could define these terms along different parameters. For example, an external or hard approach to martial arts could be found in the desire to compete in tournaments, training with ishi sashi (traditional weights) or on the makiwara (striking post). Soft or internal approaches may be realized in preventive measures such as verbal deescalation, awareness of one's surroundings, and cultivating health and chi through the practice of forms and meditation.
In Daoist texts the soft or yin model is commonly expressed as water. Water, the softest of all things, can eventually erode even the hardest of objects while seeking its own level and being at one with nature. As Bruce Lee famously said, "Water flows -- or it can crash! Be water, my friend."
1. Daniele Bolelli 2003. On The Warrior's Path. Frog, Ltd. 2. Michael Rosenbaum 2001. Okinawa's Complete Karate System: Isshinryu. YMMA Publication Center. 3. Donn Draeger 1974. Modern Bujutsu & Budo. Weatherhill, Inc.