What Yoga Is
Yoga is the control of the mind with the goal of spiritual peace. It is founded on ethical conduct and calm-inducing mental habits. Physical practice begins with postures (asanas) which train the body-mind complex. The next step is breath control (pranayama), a direct means of controlling the mind. Linked with this is the control of the sense organs. Yoga philosophy underpins these practices, giving them perspective and depth. Meditative states, the culmination of Yoga, are the fruit of practice arising from stilling the senses and concentrating the mind.
Yoga originated in India and is first mentioned in ancient Sanskrit works that are several thousand years old. It was codified as a system of practices about 2,000 years ago by Patanjali, whose classic treatise, the Yoga Aphorisms (Yoga Sutra), is still studied by Yoga students the world over.
Yogic practices for spiritual development have historically been used by people of diverse outlooks and beliefs. However, Yoga itself is founded on a philosophy (Samkhya) which teaches that the individual soul is separate from the mind. The mind consists of matter and thus belongs to the material world. Therefore by controlling and transcending the functions of the mind the individual exists in a state of spiritual freedom. This is the Yogic goal of liberation.
In mediaeval times, manuals of Yoga practices were written. They give details of various Yoga postures and breath control techniques and explain their health benefits. They also explain meditation and what could be considered occult practices. The principal such manual is the Light on the Yoga of Force (Hatha Yoga Pradipika).
The modern popularity of Yoga is due to a number of nineteenth and twentieth century Indian gurus who attracted disciples in large numbers and spread their teachings abroad. Notable among them are Swami Shivananda, Swami Kuvalayanada, Swami Satayananda, Paramahamsa Yogananda. The focus of each school is different.