‘Atideśa,’ the principle of extending or transferring the details of a particular rite to other similar rites, is often resorted to, in Vedic sacrifices. Generally, the model (or archetype) sacrifice which contains all the details, is known as ‘prakṛti’ and the derived (or ectype) sacrifice as ‘vikṛti.’ For instance, ‘Iṣu’ is a vikṛti sacrifice and many of its details are to be adopted by atideśa from its prakṛti, the Śyena.
Atideśa may be provided by ‘vacana’ (Vedic text) or ‘nāma’ (name). When a Vedic text clearly states that the details of the particular sacrifice are to be filled from another already described, the atideśa is by vacana. When two rites have similar names, the details of one have to be derived from the other. For instance, the rite Māsāgnihotra (prescribed as part of Kuṇḍapāyināmayana, another rite) and the more common Agnihotra have similar names. Hence those of the details of Māsāgnihotra which are not mentioned, or, taken for granted, should be adopted by atideśa from the latter. This is atideśa by name.