No prohibition is made against improvising variations on, rewording, or challenging the Smriti. The Smriti includes the two great Sanskrit epics, the Mahabharata and the Ramayana the many Sanskrit Puranas, including 18 great Puranas and several dozen more subordinate Puranas and the many Dharmashastras and Dharmasutras (textbooks on sacred law), of which the one attributed to the sage Manu is the most frequently cited. The practical compendium of Hinduism is contained in the Smriti, or “what is remembered,” which is also orally preserved. The actual content of this canon, however, is unknown to most Hindus. The Vedas, including the Brahmanas and the Upanishads, are regarded as revealed canon ( shruti,”what has been heard ”), and no syllable can be changed.
Between the 8th century BC and the 5th century BC, the Upanishads were composed these are mystical-philosophical meditations on the meaning of existence and the nature of the universe.
At this time, too, the Brahmanas-lengthy Sanskrit texts expounding priestly ritual and the myths behind it-were composed. A fourth book, the Atharva-Veda (a collection of magic spells), was probably added about 900 BC. The Rig-Veda was supplemented by two other Vedas, the Yajur-Veda (the textbook for sacrifice) and the Sama-Veda (the hymnal). This text, probably composed between about 15 BC and consisting of 1028 hymns to a pantheon of gods, has been memorized syllable by syllable and preserved orally to the present day. The oldest of the four Vedas is the Rig-Veda, which was composed in an ancient form of the Sanskrit language in northwest India. The ultimate canonical authority for all Hindus is the Vedas.