Thread or string'. These texts form the last stage of Vedic literature, with verses written in very technical language, by different writers between 500 and 200 BC. These works developed as a result of the need to simplify the rites and rituals explained in the Brahmanas. These concise treatises simplify Vedic teachings on rituals and their reasons. They also simplify the concepts of customary law. They are known as the "angas" or limbs of the four Vedas, but are considered smriti.

There are three known groups of text called sutras: Shrautasutras, Grihyasutras and Dharmasutras, together known as the Kalpa Sutra,and are considered attached to the Vedas.(Outside the Kalpa Sutras are other independent texts, not attached to the Vedas, also called Dharmasutra and Grihyasutras) The Shrautasutras contain short passages of instruction for the performance of the elaborate rituals described in the Vedas. For example, they explain how to lay the sacrificial fire, or how to perform Chaturmasya. The authors of the Shrautasutras belonged to different schools of philosophy. Some of the important Shrautasutra works are: The Ashvalayana and Sankhayana, associated with the Rig-Veda (see Veda). The Jaimini, Manasaka, Latyayana, and Drahyayana, associated with the Sama Veda.

The Baudhayana, Manava, Bharadvaja, Apastamba and Hiranyakesin, associated with the black Yajur Veda. The Katyayana, associated with the white Yajur Veda.

The Kaushitaki and Vaitana, associated with the Atharva Veda. The Grihyasutras deal with household ceremonies or other rites performed with the domestic fire (see Agni) in daily life. As a rule, these ceremonies are not performed by priests but by the householder himself (see Ashram). The Grihyasutras instruct on both the household ceremonies and on sanskaras. They explain the ritual, the

Sutramantras used and the social aspects of the sanskaras. Most Grihyasutras begin with an explanation of the marriage ceremony (see Vivaha<). Some leave out funeral rites (see Antyeshti) as a sanskaras since the ceremony is considered inauspicious. Some of the important Grihyasutras are the Apastamba Grihyasutra, the Baudhayana Grihyasutra, the Ashvalayana Grihyasutra, the Sankhayana Grihyasutra, and the Gobhila Grihyasutra. The contents of all these texts are similar, with minor differences in the performance of the ceremonies, since the authors belonged to different schools of philosophy.

The Dharmasutra deal with the rules of conduct and law. They are the oldest sources of Hindu law, with a chiefly religious point of view. They are closely related to the Vedas, from which they quote. Some important Dharmasutras are: The Gautama Dharmasutra, which has rules for interpreting texts, details about the ashrams, especially rules of conduct for the householder and information on the sanskaras, particularly the Upanayanam. It is one of the oldest Dharmasutras, and is studied by the followers of the Sama Veda (see Veda).

The Baudhayana Dharmasutra describes the differences in the religious practices followed in northern and southern India, and provides detailed information about the four castes (see Varna), and the five daily sacrifices (Panchamahayagya). It is studied by the followers of the black Yajur Veda (see Veda).

The Apastamba Dharmasutra enumerates the five unpardonable sins , and discusses certain technical terms and doctrines of Mimansa. It is considered to be part of the black Yajur Veda (see Veda).

Certain other sources divide the Sutras into six categories, known as the Vedangas or limbs of the Vedas. They are the Shiksha, which describes phonetics; the Chandanas, Sutrawhich details metre and poetic rhythm; the Vyakarana, which deals with grammar; the Nirukta, which discusses etymology; the Kalpa, which explains religious practices; and the Jyotishi, which explains astronomy.

The first four works contribute to the correct recitation and understanding of the sacred texts. The last two deal with religious rites and duties and the appropriate seasons for their performance. A Brahmin must mention the sutra his family is associated with, while formally introducing himself with the 'Abhivadaye' Gotra