Shiksha and Chandas are aids for pronouncing and reciting Vedic mantras correctly, Vyakarana and Nirukta are for understanding their meaning, and Jyotisha and Kalpa provide appropriate times and methods for performing the Vedic sacrificial rites and rituals. The origins of these six auxiliary 'sciences' are found in the Vedas. A brief description of each of them follows.
(i) Shiksha - This branch teaches the science of phonetics or pronunciation and recitation of the Vedic mantras. Any deviation in the pronunciation can change the meaning and thus mar the desired effect or purpose for which the mantras are chanted and applied in sacrifices.
(ii) Chandas - Chandas is the science of prosody. It deals with versification, or the rules for the metres in which Vedic mantras and poems were composed. There are eleven major and minor metres like, Gayatri, Anushtup, Ushnik, Trishtup, Jagati, etc. Pingala is the earliest known author of the Chanda shastra written in sutra form, which became popularly known as Pingala shastra.
According to tradition, before reciting any Vedic mantra the reciter has to pay respect to the respective rishi, devata and chandas of the mantra.
(iii) Vyakarana - Vyakarana is the science of grammar, which helps to make language clearer. It is called the 'mouth' of the Vedas.
Without it, the Vedas and all other Shruti works would be impossible to understand correctly. The earliest available text on Sanskrit grammar today is the Ashtadhyayi of Panini (c. 500 BCE). Panini wrote his work for the understanding of the Vedic and mainly the classical Sanskrit language, and especially for the style of Sanskrit spoken in his day. Though the Vedas were revealed and chanted many millennia before him, a systematic grammar for both Vedic and classical Sanskrit was first given by Panini. The Ashtadhyayi is considered to be the most basic and standard work in Sanskrit grammar today. It has been recognized as one ofthe greatest intellectual achievements of all time. Panini, however, mentions several scholars who were grammarians and lexicographers before him.
It is worth noting that some ancient grammarians like Patanjali (200 BCE) and Bhartruhari (between 450 and 500 CE) developed a spiritual philosophy out of grammar. They identified the eternal aspect of sound with Brahman (shabda Brahman) of Vedanta by writing the Mahabhashya and Vakyapadiya respectively. Vyakarana also includes dictionaries like Amarakosha, Halayudhakosha and others.
(iv) Nirukta - There was a Sanskrit work called Nighantu, now extinct, which was a dictionary of difficult Vedic words. The work is attributed to Yaska by some scholars, but it is not certain who the real author was. According to Yaska, the difficult words were collected and classified by the descendants of ancient sages.
The Nirukta is the oldest Indian treatise on etymology, philology and semantics, also ascribed to Yaska. The work is available today, and it is a commentary on the Nigbantu. It thus enables one to understand the Vedas. Sage Yaska was the last of the commentators on Nigbantu. His work on Nirukta is the best known work available. It is considered to be the earliest Vedabhashya or commentary on the Vedas. It consists of three parts: (1) a list of synonyms called Naighantuka Kanda, (2) a list of words used only in the Vedas called Naigama Kanda, and (3) a list of words relating to deities and rituals known as Daivata Kanda. In the Daivata Kanda, Yaska gives the etymological explanation of the names of the deities. Finally, Nirukta ends with instructions, teachings and eulogies of the Vedic devas.
(v) Jyotisha - Jyotisha is the Vedic science of astrology that includes astronomy, geometry and mathematics. Movements of the sun, moon, planets and constellations are observed and recorded in order to fix suitable days and auspicious times for the commencement and conclusion of sacred rites and yajnas for various purposes. The influence of the movement of celestial bodies on human life was also studied (astrology). References to eclipses are found in the Rig Veda.
Two Jyotisha books available from the early Vedic period are Archajyotisha of the Rig Veda with 36 verses and Yajusjyotisha of the Yajur Veda with 43 verses, and from the later period we have the Atharvajyotisha with 162 verses.
Later, the astronomy section of jyotisha science was gradually advanced by the works of Aryabhatta I (476 CE), Varahamihira (580 CE), Brahmagupta (628 CE), Bhaskaracharya I (700 CE), Aryabhatta II (c. 950 CE) and Bhaskaracharya II (1114 CE). These rishi-scientists helped in the development of Hindu astronomy and astrology.
(vi) Kalpa - The ritualistic Vedanga is called kalpa comprising the following four types of works written in sutras (aphorisms) :
1. Srauta-sutra – dealing with the Vedic rituals. These contain details about Vedic sacrifices. Each Veda had its own srauta-sutras, e.g., Asvalayana-srauta-sutra and Samkhayana-srauta-sutra belonging to the Rgveda.
2. Sulba-sutra – closely connected with the Srauta-sutras above are these sutras dealing with the measurement of sacrificial altars; sulba means the measuring tape. These are the earliest works on Indian geometry, and occupy a significant position in the history of mathematics.
3. Grhyasutra – dealing with rituals right from the ceremony of impregnation (niseka or garbhadhana) to funeral rite (antyesti-kriya). These also are attached to particular Vedas. For instance, the Asvalayana and Samkhayana Grhyasutras belong to the Rgveda.
4. Dharmasutra – dealing with rules and regulations relating to the four castes and four stages of life, royal duties (raja-dharma) and secular law (vyavahara).
Besides the above works, some works of the type of Index were written for determining the rsis, deities and metres of the hymns of the Rgveda. Thus, we have Arsanukramani, Devanukramani and Chando'nukramani. The Anuvakanukramani contains index to the anuvakas into which hymns, rather the Mandalas (books) of the Rgveda are sub-divided. Katyayana's Sarvanukramani, as the title indicates, contains all the aforesaid anukramanis. The Brhaddevata of Saunaka lists the names of the rsis to whom are ascribed the rks of the hymns.