The Eight Gates are said to be associated with the eight trigrams (Bagua 八卦 bā guà) of the I Ching, the Five Steps with the five elements of the Taoist "Wu Hsing" (五行 wǔ xíng); metal, water, wood, fire, and earth. Collectively they are sometimes referred to as the "Thirteen Postures of T'ai Chi Chuan" and their combinations and permutations are cataloged more or less exhaustively in the different styles of solo forms which Tai Chi is mostly known for by the general public. Pushing hands is practiced so that students have an opportunity for "hands-on" experience of the theoretical implications of the solo forms. Traditional internal teachers say that just training solo forms isn't enough to learn a martial art; that without the pushing hands, reflex and sensitivity to another's movements and intent are lost. Each component is seen as equally necessary, yin and yang, for realizing the health, meditative, and self-defense applications.