Ashtanga, the eight limbs of yoga, is Patanjali's classification of classical yoga, as set out in his Yoga Sutras. He defined the eight limbs as yama (abstinences), niyama (observances), asana (postures), pranayama (breathing), pratyahara (withdrawal), dharana (concentration), dhyana (meditation) and samadhi (absorption). The eight limbs form a sequence from the outer to the inner. Postures, important in modern yoga, form one limb of Patanjali's scheme; he states only that they must be steady and comfortable.