The word Veda is often derived from 5 roots these days :
1. Vid jnane: To know
2. Vid sattayam: To be
3. Vid labhe: To obtain
4. Vid vicharane: To consider
5. Vid chetanakhyananiveseshu: To feel, to tell, to dwell
To this roots is added the suffix 'ghaw' according to Ashtadhyaayi 3.3.19. Accordingly, the word Veda means 'the means of which, or in which all persons know, acquire mastery in, deliberate over the various lores or live or subsist upon them."
It signifies a vast body of sacred and esoteric knowledge concerning eternal spiritual truths revealed to sages (rishis) during intense meditation. They have been accorded the position of revealed scriptures and are revered in Hindu religious tradition. Over the millennia the Vedas have been handed over from generation to generation by oral tradition and hence the name "shruti" or "that which is heard". According to tradition they are un-authored (apaurusheya) and eternal.
EXTENT AND CLASSIFICATION OF VEDIC LITERATURE
The Vedas are four in number - Rigveda, Yajurveda, Saamaveda and Atharvaveda. According to tradition, each Veda can be divided into four parts - mantras, braahmanas, Aranyakas and the Upanishads. A collection of mantras is called a samhitaaa. Conventionally speaking it is only the samhitaa portion which is referred to as the Veda i.e., Rigveda means only Rigveda samhitaa. The braahmanas, Aranyakas and the Upanishads have their own names and are more like the theological treatises of the Vedas. A few scholars include even the Kalpasutra texts in the word 'Veda'. In the case of the Rigveda, Saamaveda and the Atharvaveda, there is a clear-cut distinction of the samhitaa from the other portions. In contrast, the Yajurveda is of two types: Shukla (or white) Yajurveda and Krishna (or black) Yajurveda. In the latter, the samhitaa and the Brahmana portions are intermixed. Likewise, there is often no clear-cut distinction between the braahmanas and the Aranyakas, and the Aranyakas and the Upanishads. The braahmanas often merge into the Aranyakas and many old Upanishads are actually embedded in the Aranyakas.
This brings us to the definition of Mantra, Braahmana, Aranyaka and Upanishad. The mantras are basically hymns sung to the Gods - the devotional outpourings of the souls of poets. The samhitaas of the four Vedas are complied for the smooth performance of Vedic sacrifices. Four priests are needed to perform a Vedic sacrifice: a Hotr priest who sings hymns to Gods inviting them to preside over the sacrifice, an Udgaataa priest who sings sweet hymns in musical tones for the entertainment of the Gods, an Adhvaryu priest who performs the sacrifice according to strict ritualistic code and makes the offering to the Gods and a Brahmaa priest well versed in all the Vedas who supervises the sacrifice. The four samhitaas - Rik, Saama, Yaju, and Atharva - are said to be compiled to fulfill the needs of the four main priests: Rik samhitaa for the Hotr, Saama for the Udgaataa, Yaju for the Adhvaryu and the Atharva for the Brahmaa priest. Mantras are basically of 3 major types, when classified according to their mechanical form: Rk, Yaju and Saama. Rik mantras are versified mantras. Yajus are prose mantras whereas Saamans are melodies set on Rik mantras. The Rigveda is so called because it is comprised primarily of Riks. The Yajurveda is composed predominantly of prose mantras (and even the Riks are recited as if they were prose passages) whereas the Saamaveda samhitaa is composed of Riks, which are used as the basis of melodies called Saamans. The Atharvaveda is comprised of Riks (5/6) as well as Yajus (1/6). Some adept Vedic scholars can set even the mantras of Atharvaveda to melodies.
Unlike the mantras, which are mostly in verse, the braahmanas are predominantly written in prose. They contain formulas for rituals, rules and regulations for rites and sacrifices and also outline other religious duties. The formulas and rules for conducting extremely complex rituals are explained to the minutest detail. And every ritual is performed for a specific purpose for which a specific effect/benefit is expected. It was felt that there was nothing that could not be achieved by sacrifices - the sun could be stopped from rising and Indra, the chief of gods, could be deposed from his throne. The observance of the caste system and the four stages of life (Ashrama), the eternity of the Veda and the supremacy of the brahmin caste are other subjects dealt with in the braahmanas.
The symbolic and spiritual aspects of the sacrificial religion are meditated upon in the Aranyakas while philosophical issues are discussed in the Upanishads. (The contents of the Upanishads are dealt with in a separate section).
CONTENTS OF THE SAMHITAAS AND BRAAHMANAS : A GENERAL SURVEY
1. The Rigveda samhitaa comprises of 10552 mantras in 1028 hymns. This hymns are divided into 10 books called the 'mandalas'. Mandalas 2-8 are family mandalas since each of these mandalas contains hymns predominantly from 1 major family of Vedic seers. For instance, mandala VI has hymns of Bharadavaja seers, mandala 3 has hymns of Visvamitra family seers and so on. Mandala 9 has 114 hymns address to Soma. Mandalas 1 and 10 are considered later additions, for most part. The Rigveda samhitaa is often also divided into 8 parts called 'Ashtakas' which are further divided into 8 chapters each. On the whole, the Rigveda mostly consists of hymns to be sung to the various Gods. Varuna, Mitra, Surya, Savitr, Vishnu, Pusan, the Ashvin twins, Agni, Soma, Yama, Parjanya, Indra, Maruts, Rudra, Vishvakarman, Prajaapathi, Maatarishvan, Ushas, Aditi are some of the Gods encountered in the Rg Veda. Varuna - the god of the sky, Indra - the god of war and Agni - the god of fire, are more popular than Vishnu and Rudra (Shiva). Surya, Savitr and Pusan all refer to the solar deity and the GAyathri mantra is addressed to Savitr. Ushas and Aditi are goddesses.
2. Yajurveda samhitaas : There are several samhitaas of Yajurveda extant, the two major ones being the Madhyandina and the Taittiriya. The great sage Yaajnavalkya is said to have collected and edited the Ur hula Yajurveda. The Madhyandina samhitaa comprises of 1875 mantras/kandikas arranged into 40 chapters according to the order of performance of Vedic sacrifices. All but the last chapter (which is called the Ishavasya Upanishad) are employed in the Vedic ritual. The Yajurveda is largely prose, with about 700 verse mantras, most of which are directly borrowed from the Rigveda. The Yajurveda therefore is a liturgical text, but also contains sacrificial formulas to serve the purpose of ceremonial religion (yaju is derived from the root "yag" - to sacrifice). Very popular in South India, the Taiitriya samhitaa deals with detailed descriptions of sacrifices like PaurodAsha, YajamAna, Vajapeya, Rajasuya, etc The Taiitriya braahmana, the Taiitriya Aranyaka and the Taiitriya Upanishad are associated with the Taiitriya samhitaa. In the Yajur Veda Vishnu becomes more important. Naraayana and Shiva are also mentioned. Prajaapathi, the creator of the world, is identified with Vishvakarman. Brahman comes to signify the creative principle of the world.
3. The Saamaveda Kauthuma samhitaa is a purely liturgical collection where mostly hymns of the Rg Veda are set to music. The samhitaa comprises of 1875 Riks of which all but 1800 Riks are traceable to the published Shakalya recension of the Rigveda. The rest are all said to occur in the Shankhayana samhitaa of the Rigveda. The origins of Indian classical music lies in the Saama Veda. The samhitaa is divided into two broad divisions - Purvarchika, on which the Gramageya and the Aranyaka Saamans are set, and the Uttararchika, on which the Uha and the Uhya chants are set. The Ranayaniya samhitaa is not published yet but appears to be materially identical to the Kauthuma Sahmita, although its Saamans are quite different. The Jaiminiya samhitaa has approximately 1650 mantras and its Saaman tradition is quite different from the main Kauthuma tradition.
4. Atharvaveda samhitaa : It is often said that the Atharva Angirasa was originally not given the status of a Veda, but seems to have been later elevated to the position. The main theme of the Atharva Veda is cure for diseases, rites for prolonging life and fulfillment of one's desires, statecraft, penances, magic, charms, spells and sorcery. While the Gods of the Rg Veda are approached with love, the Gods of the Atharva Veda are approached with cringing fear and favor is curried to ward off their wrath. Homage is paid to them to abstain from doing harm. Sophisticated literary style and high metaphysical ideas mark this Veda. The two extant samhitaas of Atharvaveda are Shaunakiya and Paippalada. The former has 5977 mantras arranged in 20 books called 'kandas' while the latter has approximately 7950 mantras arranged in as many kandas. Among other things the text also gives us an idea of the geographical spread of the Hindu civilization then - from Gandhara (Afghanistan) to Magadha (Bihar) to Vanga (Bengal).
5. Braahmanas and Aranyakas : These are basically vast and ancient theological treatises on the Mantra samhitaas. The former mainly devolve upon the ritual significance of the hymns whereas the latter deal with the spiritual significance of the Vedic rituals. In doing so, the texts elaborate upon numerous etymologies, legends connected with individual hymns and are sometimes a sort of a commentary on the hymns they deal with.
Polytheism, monotheism, monism have all been read into the Vedic hymns. Max Muller even coined the term "henotheism", as the transitional stage between polytheism and monotheism in the hymns. It is the opinion of modern scholarship that the Vedic hymns reveal the gradual progress of philosophical thought i.e., from polytheism to monotheism to monism. This major flaw in interpretation is not surprising when it is understood that such an opinion springs from viewing Indian philosophy through a Western philosophical looking glass.
The fundamental difference between Western philosophy and Indian philosophy, especially the scriptures, is that while Western philosophy tries to uncover the real with the use of the intellect, Indian philosophy is basically an attempt to logically reconcile the world of experience with the spiritual experience of the sages. The sages - Yaajnavalkya, the Buddha, the Mahaaveera - had experienced reality - unlike Western philosophers they're not speculating, analyzing with the help of reason what reality may be - they know what it is. They have experienced it and using analogies they try to describe it.
The scriptures are not to be interpreted as progress in philosophical thought. What's claimed as polytheism and monotheism is but the identification of the various manifestations of the One Supreme Being. Monism is what the Vedic sages have as the highest teaching and numerous verses supporting this are spread across each Veda, from the first mantra portion to the last Upanishad portion : "the One real which the wise declare as many"; "Purusha is all this, all that was and all that will be"; "the real essence of the Gods is one"; "The same real is worshipped as Uktha in the Rg, Agni in the Yaju and Mahaavrta in the Saama"; "the indescribable is the ground of all names and forms, the support of all the creation"; "He is immanent in all this creation and yet he transcends it".
Likewise the different parts of the Veda - mantras, braahmanas, Aranyakas and the Upanishads - too don't signify the progress of philosophical thought. The Veda is a whole package towards spiritual liberation. One cannot directly start with the Upanishads, which teach the highest truth. One must first develop the physical, mental and moral maturity to be eligible to learn such truth. The mantras, braahmanas and parts of the Aranyakas serve such a purpose. The four parts of each Veda can also be mapped to the four stages of life (ashrama) of the twice born (dvija). As a student (brahmachaarin) one is to chant the hymns and live a life of control and virtue. As a householder (grhasta) one is to observe the injunctions laid forth in the braahmanas. In the forest dweller stage (vaanaprastha) one is to meditate upon the spiritual truths behind the rituals as explained in the Aranyakas and practice austerity. With the mental and moral maturity developed during the three previous stages one can finally take up the life of a wandering mendicant (samnyaasin) and study the highest truth taught in the Upanishads. Such is the orthodox Indian view.