The following are helps to success in Yoga and are called Niyama or regular habits and observances; Tapas, austerity; Svâdhyâya, study; Santosha, contentment; Shaucha, purity; Ishvara-pranidhâna, worshipping God. Fasting, or in other ways controlling the body, is called physical Tapas. Repeating the Vedas and other Mantras, by which the Sattva material in the body is purified, is called study, Svadhyaya. There are three sorts of repetitions of these Mantras. One is called the verbal, another semi-verbal, and the third mental. The verbal or audible is the lowest, and the inaudible is the highest of all. The repetition which is loud is the verbal; the next one is where only the lips move, but no sound is heard. The inaudible repetition of the Mantra, accompanied with the thinking of its meaning, is called the "mental repetition," and is the highest. The sages have said that there are two sorts of purification, external and internal. The purification of the body by water, earth, or other materials is the external purification, as bathing etc. Purification of the mind by truth, and by all the other virtues, is what is called internal purification. Both are necessary. It is not sufficient that a man should be internally pure and externally dirty. When both are not attainable the internal purity is the better, but no one will be a Yogi until he has both. Worship of God is by praise, by thought, by devotion.