Veda is the highest authority in Hindu knowledge system and the authority of all other scriptures are based on the authority of the Veda. Vedas are four – Rig, Yajur, Sama and Atharva. Rigveda contains prayers to Gods (Riks are the mantras). Yajurveda has methods to use Riks for sacrifices (Yajus-Yajna). Sama Veda introduces musical notes. Atharva Veda gives ways to make life successful, and contains methods to fulfill what can be called material aspirations.