The following are the text I got from Sri Sri Nitai Das Prabhu, an ardent follower of Iskon & Srivaishnavam and a sincere devotee of Lord Sri Krishna. I pray, The Lord, Sri Krishna to give him every strength and energy to Serve the Community with his fine writing and to spread the Spiritualism. My Dandavata Pranamam to everyone who read this article. I wish and pray that every reader get his/her attain Mental Happiness through Surrendering to His Supremeness.

THE VEDAS

Introduction

The age of the Vedic scriptures - early estimations - reasons

In hundred eighties at the time of British colonialism an early generation of Indologists, headed by the appreciated translator of the Vedic texts Max Muller, came up with the a theory about the age of the Vedic texts that was fitting the Biblical calculation of the beginning of the world. Not based on tangible proves this theory about the age of Vedic texts did not have a long standing, and nowadays it is accepted only by few, let say orthodox Indologists. The great deal of early British Indology was motivated by Christian missionary considerations, is no secret. Colonel Boden founded the famous and important 'Boden Chair for Sanskrit' at the University of Oxford in 1811 with the explicit object 'to promote the translation of the Vedic Scriptures from Sanskrit into English, so as to enable his countrymen to proceed in the conversion of the natives of India to the Christian Religion'. In 1886 Max Muller, in a letter to his wife wrote: 'The translation of the Veda will hereafter tell to a great extent on the fate of India and on the growth of millions of souls in that country. It is the root of their religion, and to show them what the root is, I feel sure, is the only way of uprooting all that has sprung from it during the last 3 000 years.'

Western scholars decided to apply their own methodologies and, in the absence of reliable evidence, postulated a timeframe for Indian history on the basis of conjectures. Considering the traditional dates for the life of Gautama, the Buddha, as fairly well established in the sixth century BCE, supposedly pre-Buddhist Indian records were placed in a sequence that seemed plausible to philologists. Accepting on linguistic grounds the traditional claims that the Rigveda was the oldest Indian literary document, Max Muller allowing a time-span of two hundred years each for the formation of every class of Vedic literature, and assuming that the Vedic period had come to an end by the time of the Buddha, established the following sequence that became widely accepted:

Rigveda c. 1200 BCE
Yajurveda,Samaveda,Atharvaveda, c. 1000 BCE
Brahmanas, c. 800 BCE
Aranyakas,Upanishads, c. 600 BCE

However, later Max Muller himself admitted the purely conjectural nature of the Vedic chronology, and in the last work published shortly before his death, The Six Systems of Indian Philosophy, he admitted: 'Whatever may be the date of the Vedic hymns, whether 1500 or 15 000 BCE, they have their own unique place and stand by themselves in the literature of the world' (p.35). Obviously, despite the great endeavors of Max Muller to establish his own estimation of the time of the origin of the Vedas, some of his contemporaries, both Western and Indian scholars, such as Moriz Winternitz and Bal Gangadhar Tilak, disagreed with his chronology and postulated a much higher age for the Rigveda.

The Vedas brought by invaders questioned

Aryan invasion theory

As previously mentioned, early European attempts to explain the presence of Indians in India and the date of the origin of the Vedas, had much to do with the commonly held Biblical belief, that humankind originated from one pair of humans- Adam and Eve, (precisely, not before their common birth date, that was believed to be c.4005 BCE)-and that all peoples on earth descended from one of the sons of Noah, the only human to survive the Great Flood that occurred c. 2500 BCE. The only problem seemed to be to connect peoples not mentioned in Chapter 10 of Genesis ['The Peopling of the Earth'] with one of the Biblical genealogical lists.

One of the famous Christian historian attempting to explain the presence of Indians in India was Abbi Dubois (1770-1848), who after long sojourn in India (1792-1823) collecting a large amount of interesting materials concerning the customs and traditions of the Hindus categorically stated: 'It is practically admitted that India was inhabited very soon after the Deluge, which made a desert of the whole world. The fact that it was so close to the plains of Sennaar, where Noah's descendants remained stationary so long, as well as its good climate and the fertility of the country, soon led to its settlement.'

Nowadays more and more Indian educated scholars point out that there are no references in the Vedas about the migration from outside India. All the geographical features mentioned in the Rigveda are those of northwestern India and there are no archaeological evidences whatsoever, for the Aryan invasion theory. On the other side, there are references to constellations in Vedic works whose timeframe could be calculated. The dates arrived at are 4500 BCE for one observation in the Rigveda, and 3200 BCE for a date in the Shatapatha Brahmana. For some these seems to be far too remote to be acceptable, especially if one assumes-as many nineteenth century scholars did, that the world was only about 6 000 years old and that the flood had taken place only 4000 to 5000 years ago. But these objections have not a strong standing.

A recent major work by Klaus Klostermaier that denies Aryan invasion theory (you can read the full article on http://www.iskcon.com/icj/6_1/6_1klostermaier.html) offers 'seventeen arguments: why the Aryan invasion never happened'. Here we will mention only some of them that are relevant in our discussion about the Veads, so that we can see, that the Vedic scriptures were not imported from outside of India.

1) There is no memory of an invasion or of large-scale migration in the records of Ancient India-neither in the Vedas, Buddhist or Jain writings, nor in Tamil literature. The fauna and flora, the geography and the climate described in the Rigveda are that of Northern India.

2) The archaeological finds of Mehrgarh (copper, cattle, barley) reveal a culture similar to that of the Vedic Indians. Contrary to former interpretations, the Rigveda shows not a nomadic but an urban culture (purusa as derived from pur vasa = town-dweller).

NOTE: (Mehrgarh is located in the area of Baluchistan, and Pakistan)

3) The Rigveda describes a river system in North India that is pre-1900 BCE in the case of the Saraswati river, and pre-2600 BCE in the case of the Drishadvati river. Vedic literature shows a population shift from the Saraswati (Rigveda) to the Ganges (Brahmanas and Puranas), also evidenced by archaeological finds.

4) The astronomical references in the Rigveda are based on a Pleiades-Krittika (Taurean) calendar of c. 2500 BCE when Vedic astronomy and mathematics were well-developed sciences (again, not a feature of a nomadic people).

5) The battles described in the Rigveda were not fought between invaders and natives but between people belonging to the same culture.

6) The Rigveda itself shows an advanced and sophisticated culture, the product of a long development, 'a civilisation that could not have been delivered to India on horseback' (p.160).

Conclusively, even these few discoveries prove the origin of the Vedic culture and literatures as not something that was imported by uncivilized nomads concerned only with the maintenance of their tribal economy.

The beginning of kali yuga and the Vedas

Regarding Vedic chronology Max Muller wrote:  "Whether the Vedic hymns were composed 1000 or 1500 or 2000 or 3000 years B.C. no power on earth will ever determine."

This statement of Max Muller is easily rejected on the strength of the previous references, and so, nowadays more and more western archaeologists place the date of Indus civilization between 3250 and 2750 B.C. Gradually the proper date of the origin of the Vedic scriptures is becoming established which corresponds to the calculations given in the Vedic texts, when Srila Vyasadeva wrote down the Vedas.

The beginning of the kali yuga, according to the astronomical information from Mahabharata and other Vedic scriptures, started at 2:27a.m. on February 18th in the year 3102 B.C. exactly when Lord Krishna had left this planet after 125 years and 4 months of His earthly pastimes. It is also described that the arrival of Kali yuga was witnessed by the great heroes of Mahabharat like Yudhistira.

Conclusively, because the Vedic scriptures, as mentioned in the Srimad Bhagavatam and other Vedic texts, were written by Srila Vyasadeva at the beginning of the Kali yuga age, they are roughly 5000 year old. Any other calculations of the age of the Vedic scriptures are certainly wrongly motivated, just to minimize the value of Vedic texts and the Aryan civilization, as that was done by Max Muller and other Christian missionaries.

Division of the Vedas

According to tradition, each Veda can be divided into two parts - Mantras and Brahmanas. A collection of Mantras is typically called a Samhita. Currently, and often in ancient Vedic tradition as well, it is often the Samhita portion which is referred to as the Veda. For instance, the word 'Rigveda' would typically mean the Rigveda Samhita.  

The Brahmanas have their own names and are more like theological treatises of the Vedas. The end portions of many Brahmanas have an esoteric content, called the 'Aranyakas'. Embedded in these Aranyakas, or at their very end, are deeply spiritual treatises called the 'Upanishads' (upa=near, ni=down, shad=sit). They were taught to those who sat down beside their teachers to become enlightened with spiritual understanding.

Further, the Vedanta-sutra, which consists of codes revealing the method of understanding Vedic knowledge, is the concise form of all Vedic knowledge. It begins with the words athato brahma-jijnasa: "Now is the time to inquire about the Absolute Truth". According to the great dictionary compiler (Kosakara), Hemacandra, Vedanta refers to the purport of the Upanishads and the Brahmana portion of the Vedas. Supported by the Upanisads the Vedanta-sutras are known as nyaya-prasthana, legitimate logic and argument concerning cause and effect giving the conclusive understanding of the sruti-prasthana, the Upanishads.

Nyaya, Srutis and Smritis

In Vedic culture, the available body of knowledge comes from the revealed scriptures. The scriptures are mainly of three categories: nyaya-prasthana, sruti-prasthana and smrti-prasthana. The nyaya-prasthana includes the literature known as Vedanta-sutra - the ultimate conclusions of the Vedas. The sruti-prasthana comprises the four Vedas with their subsidiary branches like the Samhitas (mantras and prayers), Brahmanas (explanations how to use the Samhitas), Aranyakas (texts for hermits in the forest), Upanishads (secret teachings, most important in philosophical aspect). The third division of the Vedas the smriti-prasthana consists the Puranas, Mahabharata (that includes the Bhagavad-gita), Samhitas and Itihasas (histories), the Ramayana etc.

So, the Vedanta sutras are known as nyaya-prasthana, or fully logical arguments towards the conclusive understanding of sruti-prasthana, the Upanisads and the Brahmaëa portion of the Vedas. According to the great dictionary compiler Hemacandra, the supplement of the Vedas is called the Vedanta-sutra - the ultimate knowledge of the Vedas, and the Upanisads support its conclusions.

Sruti refers to the four Vedas, which once upon a time became manifested from Lord Brahma when he began to think how to create the worlds. Sruti is composed in Vedic Sanskrit and smrtis in laukika Sanskrit. There are some basic differences between these two types of Sanskrit. E.g., the Vedic Sanskrit has its own grammar and it is used only in the Vedas. 

Moreover, the words of the Vedic Sanskrit have accent, similar to notes in music, and the meaning of the word can change drastically simply by changing the accent of its letters. Therefore, these words have to be heard properly from the guru in the disciplic succession and hence the Vedas are called sruti (lit. hearing). Nobody has the authority to change even a single syllable of the sruti. They are passed on from one age to another. Sometimes some parts of srutis get lost due to break in disciplic succession. Then they are again heard in trance by great sages called rsis. Rsi means a seer, or one who sees the Vedic texts. He hears it in trance and realizes its meaning. Thus, e.g. the Upanisadic texts contain the conversations of self-realized sages based on their realizations of that spiritual knowledge.

Smrtis on the other hand are written in laukika Sanskrit or Sanskrit spoken by people. It does not have accent in its words. Itihasas, Puranas, Agamas are all part of smrtis. Among the smrti literature there is a body of literature which is also called smrti such as Manu-smrti. These smrtis are part of dharmasastra or books giving religious code. Smrti sastras are compiled by remembering the meaning of the sruti and that's how the name smrti (lit. remembrance) comes about. The smrtis change from age to age in their structure but the essence is same.

The four Vedas: Rg, Sama, Yajur and Atharva

According to the Vayu Purana, before Kali yuga there was only one Veda - the Yajur Veda. In the beginning of the Kali yuga however, Srila Vaysadeva devided it into four branches. This is described in two Puranas namely the Srimad Bhagavatam and the Kurma Purana (52.19-20) as well: 

"The Rgveda was divided into 21 branches and the Yajurveda into 100 branches, the Samaveda into 1,000 branches and the Atharvaveda into 9 branches."

Further, every branch was divided into four subdivisions called Samhita (or Mantra), Brahmana, Aranyaka, and Upanisad. Thus altogether, the Vedas consisted of 1130 Samhitas, 1130 Brahmanas, 1130 Aranyakas, and 1130 Upanisads, a total of 4520 titles. By the influence of time, however, many texts have been lost. At present only about 11 Samhitas, 18 Brahmanas, 7 Aranyakas, and 220 Upanisads are available. This is less than 6% of the original Vedas.

The structure of the four Vedas

In the first canto of Srimad Bhagavatam it is describes that formerly there was only one Veda called Yajur Veda in which four division of sacrifices were mentioned. However, in the beginning of the Kali yuga srila Vyasadeva divided that one Yajur Veda into four Vedas namely: Sama, Yajur, Rig and Atharva which corresponded to the four divisions of the sacrifices.

In the case of the Rigveda, Samaveda and the Atharvaveda, there is a clear-cut separation of the Mantra collection from the Brahmana portions. In contrast, the Yajurveda is of two types: Shukla (or white) Yajurveda and Krishna (or black) Yajurveda. In the former, the Mantra and Brahmana collections occur separate from each other. In the latter, the Mantra and the Brahmana portions are intermixed. Thus, the Taittiriya 'Samhita' belonging to the Krishna Yajurveda has Mantras put together with Brahmana portions. Even the Taittiriya 'Brahmana' has both Mantras and Brahmana passages mixed with each other.

 Coming to the Brahmana texts, there is often no clear-cut distinction between the Brahmanas proper and the Aranyakas, or between the Aranyakas and the Upanishads. The Brahmana text proper often merges into the Aranyakas and many old Upanishads are actually inserted within the aranyakas.

 There are a few exceptions even to the above generalizations on the internal distinctions in the Vedic texts.

The Samhitas

The Samhitas or mantras of the four Vedas are basically hymns sung to the demigods and are especially chanted for the smooth performance of Vedic sacrifices. Four types of priests are needed to perform a Vedic sacrifice:

The Hotra priest who sings hymns to Lord Visnu and the demigods inviting them to preside over the sacrifice,

The Udgata priest who sings sweet hymns in musical tones for the entertainment of Vishnu and the demigods,

The Adhvaryu priest who performs the sacrifice according to strict ritualistic codes and offers oblations to Vishnu and the demigods

The Brahma priest well versed in all the Vedas who supervises the sacrifice.

The four Samhitas are said to have been compiled to fulfill the needs of these four main priests: Rg-Samhita for the Hotra, Sama-Samhita for the Udgata, Yajurveda Samhita for the Adhvaryu and the Atharvaveda Samhita for the Brahma priest. Initially however, there was no special connection of the Brahma priest with the Atharvaveda, as this Veda was and is not so closely integrated with Vedic rituals as the other three Vedas.

The Rigveda (Rg Veda)

Since out of the four Vedas this Rgveda is one of the most important we will give a bit longer explanation about it. The Rg Veda is called "the Veda of praise". Most of the verses are in praise of numerous demigods. According to many commentators the Purusa-sukta found in this Veda is especially praising the supreme position of Lord Narayana who according to the Rgveda is the Highest Supreme Lord whereas Agni is the lowest. Actually the most of the Rgvedic hymns praise various deities like Vishnu, Indra, Varuna, Agni, Savita, Marut, Mitra, etc. The hymns in praise of individual demigods are known as suktas. In the description of different factors related to the demigods we find informations about historical, political and geographical conditions of ancient Vedic times. Further, many suktas of the Rgveda deal with topics like ethics, philosophy, religion, culture etc.  

Few Philosophical tenets in the Rgveda

Atma, Paramatma, creation, genesis, death, rebirth, liberation etc. are all deeply and exhaustively discussed in the Rgveda.  

a) Ishvara, Jiva, Prakriti: are considered the three factors of creation and administration of the universe. Ishvara is the main cause of creation who impregnates the Jivas in to the Prakriti to give them all facility to attain liberation from the repeated birth and death - samsara. The Jiva actually attains freedom from the bondage and liberation from Prakriti when he realizes his own true spiritual nature in relation to Ishvara. Many mantras in Rgveda describe this three factor points.

b) Creation:  There are about 6 to 7 suktas in Rgveda regarding the genesis of this Universe. The Nasadiya, Hiranyagarbha and Purusha suktas are the most famous.   The Nasadiya sukta (10.129) describes the condition before the creation, and evolution of the Universe. "In the beginning there was nothing. There were neither worlds nor momentum, neither birth nor death nor immortality, neither day nor night. Only the Omnipotent, supreme Purusa, existed. When He desired to create the seed of creation and the demigods were born. The supreme Purusa is the only Lord of this creation and He alone should be known and understood". The Hiranyagarbha sukta also describes the process of creation. "In the beginning of the material creation the Hiranyagarbha - Parmatma alone existed. He was the sole Lord of all created beings. He bears on his person the earth and celestial worlds".

The Sama-Veda

The Sama-Veda called the "Veda of chants" contains some hymns from the Rg Veda transfered and re-arranged, without reference to their origin. Here the verses are not chanted but sung in specifically indicated melodies using the seven svaras or notes. Such songs are called Samagana and in this sense the Sama Veda is really a book of hymns. The Sama Veda is chanted during the performance of soma-yagyna. The Gandharva-veda is the Sama Veda's upa-veda.

Yajur Veda

Known as "the sacrificial Veda", the Yajur Veda contains texts pertaining to the performance of sacrifices. This Veda is divided into two parts: the Taittiriya-samhita and the Vajasaneyi-samhita. The first part is also called the black (Krishna) Yajur Veda for its Samhita and Brahmana portions intermix. The second is called the white (shukla) Yajur Veda because its Samhita portion is quite separate from its Brahmana portion. The Dhanur Veda (or military science) is the Yajur Veda's upa-veda. The Sthapatya-veda (or architectural science) and the Shilpa-sastra (or knowledge of art) are also indirectly connected to this Veda. the Yajur Veda known the Krishna ("black") Yajur Veda mostly used in south India and the Shukla ("white") Yajur Veda that is most known in the north of India. Both contain almost the same material of approximately 2000 mantras borrowed form the Rgveda Veda plus many other prayers chanted during the sacrifices in which the ultimate beneficiary of all such sacrifices is said to be the Supreme Lord, Vishnu.

Briefly, Yajur Veda is like a manual for sacrifices that have to be performed for the successful running of the household, the business, the kingdom. There are sacrifices for getting rain and seasonal offerings connected with agriculture. The longest sections in the Yajur Veda are devoted to the soma sacrifice, how to build the fire altar and the ashvamedha or horse sacrifice.

To successfully perform the famous soma sacrifice there are many preparations to be done already one year in advance, for example, the building of the huge altar from 10,800 bricks and the collecting of many other rare ingredients. Other things that are described in the Yajur Veda are: dharma, karma, respect for family, cow worship, varnasrama, the existence of heaven and hell, reincarnation, the nature of the demigods, Lord Vishnu, need of overcoming material desires,  how should a yoga practitioner purify his mind to become eligible to elevate his consciousness, liberation from rebirth, etc.

Atharva Veda

The Atharva Veda contains prayers and magic chants. Some of the rites described in the grihya-sutras come from the Atharva Veda. The Atharva Veda is the first Vedic text dealing with medicine: It is surprisingly advanced for its age and outlines a clear germ theory. That is, it identifies the causes of disease as living causative agents. Besides descriptions of how to perform various rituals and the important philosophical tenets the Atharva Veda also gives insight into the Aryan warfare describing a variety of devices such as the arrow with a duct for poison (apaskambha) and castor bean poison, poisoned net and hook traps, use of disease spreading bugs and smoke screens find a place in the Atharva Veda samhita.

The Brahmanas

Commenting on Taittiriya Samhita 1.2.1, Bhatta Bhaskara defines 'Brahmanas' as texts which explain the Vedic mantras and Yajnas. In chapter 2 of his Kavyamimamsa, Rajasekhar defines the Brahmanas as texts which are characterized by statements of praise, criticism, disapproval, and explanation and application of ritualistic mantras.

There is no sharp difference in the characteristics of the Mantra and the Brahmana portions of the Vedas. However, unlike the mantras, which are mostly in verse, the Brahmanas are predominantly prose. The Brahmanas 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. For example, it is said that nothing could be achieved without sacrifices and even the sun would stop from rising. The duties of men professing different occupations, the eternity of the Veda, popular customs, cosmogony, historical details, praise of ancient heroes are some other subjects dealt within the Brahmanas.

Some of the well known Brahmanas are the Aitareya, Taittiriya, Kaushitaki, Shankayana, Shatapata, Talavakara (Jaiminiya), Gopatha and Chandogya Brahmanas.

The aranyakas

The Aranyakas constitute the Brahma kanda -the last section of Karma kanda (the treatise on rituals). They were studied by ascetics together with their students that moved into the forest to study the spiritual doctrines. Thus the Aranyakas or forest texts give less emphasis on the sacrificial rites then the Brahmana texts used in the towns. The Aranyakas are considered to be transitional literature between the Brahmanas and the Upanishads. Although they still discuss rites they explain their mystical aspects and the nature of God. They give the conduct for dharma (the correct religious path to follow), Achara (tradition), vidhi (procedure and duty), nishedha (prohibitions), lists of formulas and some hymns from the Vedas as well. Moreover, Aranyakas contain a lot of intellectual discussions that are later even more elaborated in the Upanishads.

Most Brahmanas have one or more Aranyakas associated with them. For example, the Aitareya and Kaushitaki Aranyakas are associated with the Aitareya and Kaushitaki Brahmanas of the Rig-Veda. However, it is not known that there are Aranyakas associated with the Atharva Veda. Some of the well known Aranyakas are the Taittiriya, Shankhayana, Devatadhyaya, Samavidhana, Panchavinsa(Tandya), Shadwinsha and Arsheya Aranyakas.

Degrees of education

There are four degrees of education in Vedic knowledge that corresponded to the four asramas of brahminical culture (the brahmacari or Student asrama, the grhastha or householder asrama, the vanaprastha or retired asrama and the sannyasa or renounced asrama).  The first degree of learning is the memorization of the Vedic Samhitas, which consists of thousands of mantras (verses) divided into four sections Rg, Sama, Yajur and Atharva. The second degree is the mastery of the Brahmana portion of the Vedas, which educates one in  rituals for fulfillment of duties to family, society, demigods, sages, other living entities and the Supreme Lord.  The third degree is the mastery of the Aranyaka portion of the Vedas, which prepares the retired householder for complete renunciation.  The fourth degree is the mastery of the Upanisads, which present the philosophy of the Absolute Truth to persons seeking liberation from birth and death.

The Upanisads

The symbolic and spiritual aspects of the sacrificial religion are meditated upon in the Aranyakas while philosophical issues are discussed in the Upanishads. They teach the path of knowledge, one could say, as opposed to that of the rituals (karma-kanda) expounded in the Brahmanas, and Aranyakas. Although related to the Brahmanas and Aranyakas the Upanisads reveal only the Absolute Truth, and impart higher confidential knowledge. Although some Upanisads can be interpreted in a way that they describe the ultimate Truth to be the Impersonal Brahman, when one takes to consideration all the Upanisads and especially the Isa Upanisad, the Gopala-tapani Upanisad, the Katha Upanisad etc., it becomes clear that the Ultimate Supreme Absolute Truth is a person. For example, the Katha Up. 1.3.10 explains that: 'Higher than senses are the sense objects; higher is the mind; higher is the buddhi; higher is the soul and still higher the avyakta. Then it says: avyakta purusah para purusa na param kincit sa kastha para gatah. The Purusa, the Personality of Godhead, is superior to the Avyakta. He is the ultimate Entity beyond Avyakta, the supreme goal.

According to the Indologists, the Upanisads related to the Aitreya and Kaushitaki schools are respectively called Aitreya and Kaushitaki Upanisads. Those of the Tandi and Talavakara schools of the Sama Veda are called Chandogya and Kena (or Talavakara) Upanisads. Those of the Taittiriya school of the Yajur Veda are named Taittiriya Upanisad and Maha-Narayana Upanisad. That of the Katha school is called Katha Upanisad and that of the Maitrayani school is known as the Maitrayani Upanisad. The Brihad-aranyaka Upanisad is the direct development of the Vajasaneti school.

The Upvedas and Vedangas,

Upavedas - The supplementary texts of the four Vedas are called Upavedas or "sub-Vedas" (up means subsidiary). There are four Upvedas. Arthaveda (science of sociology and economics) is related to Rgveda; Dhanurveda (science of defense and war and the making of its related appliances) is related to Yajurved; Gandharvaveda (science of music, both singing and instrumental) is related to Samveda; and Ayurveda (the medical science) is related to Atharvaveda. The first three are almost extinct, the fourth one, the Ayurveda, is still in existence but not all of its books are available.

Vedangas - There are six Angas or explanatory limbs, to the Vedas: the Siksha and Vyakarana of Panini, the Chhandas of Pingalacharya, the Nirukta of Yaska,  the Jyotisha of Garga, and the Kalpas (Srauta, Grihya, Dharma and Sulba) belonging to the authorship of various Rishis.

Vyakarana (Sanskrit grammar) - Without knowledge of Vyakarana, one cannot understand the Vedas. Unfortunately the very ancient Sanskrit grammar books are all extinct. It is believed that there was a Mahesh grammar produced by Lord Shiva, and there was also an Aindra grammar. Both are extinct. The grammar that we have now is the Panini grammar. It has eight chapters so it is called Ashtadhyayi. It is considered that it was directly inspired by Lord Shiva. There is a famous verse in this respect: Once Lord Shiva, at the end of his ecstatic dance caused by the enchanting effects of love of Krishna, played on His damru (the mini hand-drum which Shiva holds in His hand). Fourteen very distinct sounds came out of it. Haring this within his mind, the sage Panini understood them as the science of Sanskrit grammar which already eternally existed. Thus, graced by Lord Shiva, Panini, on the basis of those Divine sounds, re-established the lost science of Vedic grammar.

Siksha - is the science of proper articulation and pronunciation of the Vedic syllables (sounds). Siksha is essential because mantras are precise sound formulas that must be executed properly if the desired result is to manifest.

Chanda - is the science of poetic meter; in the Vedas there are eleven chandas such as Gayatri, Ushnik, Anushtup, Brihati, Pankti, Trishtup, Jagati, Aticchanda, Atyashti, Atijagati and Ativirat.

Nirukta - is the science of etymology and lexicology or in other words a dictionary of words used in the Vedas and their derivatives; a famous nirukta was compiled by Yaska.

Jyotisha - is the science of astronomy and astrology. The Yajur and Rig Vedas have sections attached to them dealing with astronomy, whereas the Atharva Veda has a section dealing with astrology. Aside from the Vedas, many rishis such as Parashara, Garga, Narada, Shukadeva, Bhrgu, etc., wrote on this science and preserved it in their sampradayas (disciplic successions).

Kalpana - is the science of rituals and observations (viddhi).

The first pair of angas, siksa and chanda, teach us how to speak the Vedas. The second pair, nirukta and vyakarana, teach us how to understand the meaning of the Vedas. While the third pair, kalpana and jyotisa, teach how to use the Vedas.

The Kalpa-sutras

The Kalpa-sutras are sometime included in the supplementary category. They deal with the Vedic rituals and sacrifices somewhat like the Brahmanas.

Kalpa Sutra is mainly of four types:-

1) SHRAUT SUTRA:- It contains the description of various religious rites as mentioned in the 'Brahmans' and also the various oblations performed in the sacrificial fire.

2) GRIHYA SUTRA:- It contains the detailed description about the various oblations performed in the household like sacred thread ceremony, marriage, 'Shraadha' etc.

3) DHARMA SUTRA:- It contains the detailed description about the duties of all the four castes i.e. Brahmana, Kshatriya, Vaishya and Shudra. The duties of the king are especially emphasized. It is considered as the main 'Kalpa Sutra'.

4) SHULVA SUTRA:- It contains the methods of constructing the 'Altar' of the oblation which are based on the ancient geometrical science of the Aryans. It is considered to be very scientific.

Sutras and shastras

The sutras are a succession of concise instructions that recall, summarize or shed light on teachings that are self-evident to those who know them. Sutras are often quite hard to grasp since they require prior and implied knowledge and culture. If we lack such knowledge, it will prove very difficult for us to decode sutras. These must form a collection of instructions (codes) that express the essence of all knowledge in the minimum of words. It must be universally applicable and faultless in its linguistic presentation. Sutras or codes are generally meant to be learnt by heart and commented upon. They can be gathered together and developed to form a sastra. More often than not, a satra is a revealed work that deals with many subjects. 

Describing what are the Vedic shastras (scriptures) the Candogya Upanisad (7.1.4) says that the Puranas and Mahabharata, generally known as histories, are the fifth Veda. This is also confirmed in the Srimad Bhagavatam (1.4.20): "The histories and Puranas are said to be the fifth Veda. Vyasadeva instructed this literature known as Veda, which has the Mahabharata as its fifth part."

All these shatras were manifested from the Supreme Lord Narayana. This is decribed in the Atharva Veda 11.7.24 and Madhyandina-sruti of Brhad-aranyaka Upanisad 2.4.10:

"The Rg, Sama, Yajur and Atharva became manifest from the Lord, along with the Puranas and all the Devas residing in the heavens."

"O Maitreya, the Rg, Yajur, Sama and Atharva Vedas as well as the Itihasas and the Puranas all manifest from the breathing of the Lord."

Therefore, the Mahabharata and Ramayana, which are itihasas, and according to Madhvacarya, the Pancaratras as well, are all accepted as bona fide Vedic shastras given by the Supreme Lord Narayana.

Vedanta Sutra and Bhashyas

Vyasadeva the incarnation of Krishna compiled Vedanta-sutra to enable one to understand the Absolute Truth through infallible logic and argument. According to the great dictionary compiler (Koshakara), Hemacandra, Vedanta refers to the purport of the Upanishads and the Brahmana portion of the Vedas.

Veda means knowledge, and anta means the end. In other words, the Vedanta-sutra is the proper, conclusive understanding of the ultimate purpose of the Vedas expressed through concise sutras or codes.  The Vedanta-sutras are known as nyaya-prasthana, legitimate logic and argument concerning cause and effect giving the conclusive understanding of the sruti-prasthana, the Upanishads.

In the very beginning the special purpose of the human form of life is expressed in the sutra athato brahma-jijnasa: "Now is the time to inquire about the Absolute Truth". With this the student is introduced into method of understanding the Vedic knowledge. The Vedanta Sutra consists of four chapters. The first two chapters discuss the relationship of the living entity with the Supreme Personality of Godhead. This is known as sambandha-jnana, or the knowledge of relationship.

The third chapter describes how one can act in his relationship with the Supreme Personality of Godhead. This is called abhideya-jnana.

The fourth chapter describes the result of such action. This is known as prayojana-jnana.

The Vedanta-sutras are also known by the following different names: 1) Brahma-sutra, 2) Saririka-sutra, 3) Vyasa-sutra, 4) Badarayana-sutra, 5) Uttara-mimamsa, 6) Vedanta-darsana.

Because the Vedanta-sutra is in codes which contain a lot of knowledge, it required commentaries (bhashyas).

Sripada Sankaracharya wrote his commentary on Vedanta-sutra based on monism (advaita - not two). He established that God and the living entity are one. Not accepting the transformation of the energy of Absolute Truth, which is the actual explanation of the Vedanta-sutra, he introduced the theory of illusion. He claimed that everything is one with Supreme.

There are other (theistic) commentaries by vaishnava acharyas:

Nimbarka - dvaitadvaita (oneness and dualism)
Vishnuswami - suddhadvaita (purified oneness)
Ramanujacharya - visistadvaita (specific oneness)
Madhvacharya - dvaita (dualism)
Baladeva Vidyabhusana - acintya bhedabheda tattva (inconceivable oneness and difference)

In each of these commentaries, the Supreme Personality of Godhead is established as the cause of all causes, the cosmic manifestation is established as transformation of His inconceivable energies, and bhakti is described very explicitly.

Agamas

The Agamas are theological treatises and practical manuals of divine worship.

The word Agama in Sanskrit has a few meanings 'acquisition of knowledge', 'traditional doctrine', 'science' etc. In terms of religious significance, the Agamas are as important as the Vedas. They include Tantras, Mantras, and Yantras which mostly deal with the deity worship of God in the temples. All the Agamas discuss (i) Jnana or Knowledge, (ii) Yoga or concentration, (iii) Kriya or rituals, and (iv) Charya or worship. They also give elaborate details about the ontology, cosmology, liberation, devotion, meditation, philosophy of mantras, mystic diagrams, magic and combination of words used as a magical charm, temple-building, making deities, rules of household life, social rules, and public festivals. Although historically they are not derived from the Vedas, still they are used as important guidebooks for deity worship. Saivaits, Vaishnavas and Shaktas all have their own respective Agamas.

Saivism recognizes 28 principal Agamas and 150 sub-Agams. Various schools of Saivism such as the the Saiva Siddhantha school, Tamil Saivism, Kashmiri Saivism and Vira Saivism  follow these texts and base their religious activity upon them. These are very much like the Puranas in some respects. The texts are usually in the form of dialogues between Siva and Parvati. In some of these, Siva answers the questions put by Parvati and in others Parvati answers Siva's questions. The most prominent agama text in Saivism is the Kamika. In all of them Siva is consider to be the Supreme Ruler of the Universe, the Highest Self, the Conscious Principle while Shakti is regarded as the unconscious or the natural principle who is the cause of bondage. The union of Shakti with Siva at the highest level leads to the freedom of the soul (pasu) from the Pasa or the attachment.

The Shaktas follow 27 Agamas also called Tantras. Shaktas considers the Mother Goddess as the Supreme Self and relegate Iswara, the Divine Father, to a secondary position. In the shakta philosophy the Divine Mother is both the cause of delusion (maya) and the source of liberation. The infamous tatntric worship of the shaktas is not at all accepted by the followers of Vedic methods of worship. In their Agamas besides the mechanical, ritualistic, Tantric forms of worship there is knowledge about magic and occultism.  

The Vaishnava Agamas are grouped into four categories namely the Vaikhanasa, Pancharatra, Pratishthasara and Vijnanalalita. Of these, the Vaishanavas consider the Pancharatra Agama as the most important. These Agamas are believed to have been revealed by Narayana Himself. The Pancharatra Agama is again subdivided into seven sub-Agamas namely, the Brahma, Saiva, Kaumara, Vasishtha, Kapila, Gautamiya and the Naradiya. The Pancharatra Agamas consider Vishnu as the Supreme Lord of the Universe and devotion to Vishnu as the sure path to liberation. According to one opinion, the Vaikhanasagama is the most ancient and most important Agama and all the Agamas practically and literally copied all their information from this sacred Agama. It is believed that the Vaikhanasa Agama was originally compiled under the guidance of sage Vaikhanasa during the early Vedic period. Sri Madhavacharya held Pancharatra texts in high esteem and equated them with the Vedas and the epics, while Sri Shankaracharya had a different opinion. 

According to another classification the Agamas are of five types namely: Sakta Agamas, Soura Agamas, Ganapatya Agamas, Saiva Agamas and Vaikhanasa Agamas.

The Pancharatras

The Pancharatra system is spoken by the Supreme Personality of Godhead (just like the Bhagavad-gita); there are 108 Pancharatra books in which the system of worship of the Lord in His Deity form is explained to and through the great authorities of bhakti, viz., Lord Brahma, Lord Siva, Goddess Lakshmi etc., Padma Pancharatra, Narada Pancharatra, Hayasirsa Pancharatra, Laksmi-tantra, and Mahesa Pancharatra are some of the most important books of Pancharatra.

Under the Vedic vidhi (rules) a student is required to be a bonafide son of a brahmana or twice born, but a sudra can be elevated to a brahmanas position by Pancaratrika vidhi.

As human society becomes degraded by the influence of the age of Kali, people become unfit for the vedic system. So the Pancharatra system of making one qualified by initiating him into the process of bhakti by which he is engaged fully in the service of the Deity form of the Lord.

Pancharatra books contain elaborate descriptions on the subject matter of the expansions and incarnations of the Supreme Personality of Godhead, especially the Deity incarnations, detailed information on day to day worship of the Deity forms, methods of purification of the worshipper and process of practical meditation, process of installing temple and Deities, and instructions on how to conduct different festivals in glorification of the pastimes