The words 'Upanishat' occurs in apposition to the word 'Nishat' as early as in Rigveda Khila. According to Max Mueller, Upanishad literally means "sit down near" (Upa - near, ni - down, shad - sit) which meant that the spiritual aspirant had to sit devotedly near the teacher to learn the doctrine. This suggestion has caught on rapidly, and is accepted by many modern scholars like Dr. Sarvapalli Radakrishnan. However, many traditional scholars frown upon this etymology and point out that it is ungrammatical. The earliest definitions of the word 'Upanishad' are available in the extant fragments of Vakyakara, Brahmandin and Bhashyakara Dramidacharya - two pre Shankaracharya commentators on Vedaanta who are quoted profusely by later Vedaantins like Sudarshana Suri. Following are these fragments:

Vakyakara: "Upanisannatvad upanisat"- "The term Upanishad derives from the fact that it is put down."

Dramidabhasyakara: Gahane hiyam vidya samnivista"- "For this meditation is contained in the Mysterious One (that it is called Upanishad)"

ENUMERATION OF THE UPANISHADS

The total number of extant Upanishads exceeds 200. Most of these texts are clearly late, and are not considered authoritative by all Hindus. The Muktika Upanishad, a text dating to around 1000 C.E., lists 108 Upanishads.

By tradition, fourteen are considered as the principal Upanishads. They are Isha, Kena, Katha, Prashna, Mundaaka, Maandukya, Taiitriya, Aitreya, Chaandogya, Brhadaaranyaka, Shvetaashvatara, Kaushitaki, Mahaanaaraayana and Maitri. Recently, the following ancient Upanishads have been discovered in manuscript and have been published: Arsheya, Chhagaleya, Shaunaka, Pranava, Katha Shiksha and Baskhalamantra. The last even has a commentary attached to it, which closely resembles the other commentaries of Shri Shankaracharya.

It is noteworthy that there are several other texts embedded in the Vedas and elsewhere that resemble the Upanishads very closely in their thought. Examples are: The Brahmasukta of the Atharvaveda, the Adhyatma Patala of the Apastamba Dharmasutra and so on.

While many of these Upanishads present Vedaantic thought, some late ones are sectarian, or are inclined towards Yoga and Sannyasa. Apparently, these texts were named as Upanishads because the word had acquired an aura or simply because these texts represent the esoteric, secret spiritual doctrines of their respective sects.

RELATIONSHIP OF UPANISHADS WITH VEDIC LITERATURE

It is generally believed that the mantras, the Braahmanas and parts of the Aranyakas constitute the karma kaanda or the works section of the Vedas, the Upanishads are the jnaana kaanda or the knowledge section. In reality however, the mantras are ancient collections covering a wide range of topics including rituals, ethics, spirituality, cosmology and so on. The Braahmanas are theological treatises, largely dealing with Vedic ritual, and rubricating these mantras in the rituals expounded. Often appended to these Braahmanas are esoteric texts called the Aranyakas. And in these Aranyakas, are embedded the Upanishads. However, many Upanishads are stand alone texts which might not have been integral with the Aranyakas. While the subject of the karma kaanda is dharma, the subject of the jnaana kaanda is Brahman or reality. The Upanishads are also called the Vedaanta (Veda - scripture, anta - end of) or the end of the Veda i.e., the final purport of the Vedas. This is because of two reasons: They generally occur at the end of the Samhita-Braahmana-Aranyaka literature; and because they represent a culmination or the 'final view, or essence' (siddhanta) of the Vedic philosophy.

All extant Upanishads are traditional classified under one of the 4 Vedas. Sometimes, this classification is opposed to the correct ancient placement of the Upanishads in the Vedic cannon, and in the case of late Upanishads, such a classification often appears artificial. Appendix 1 groups the various ancient Upanishads under different Shakhas of the Vedas.

DEVELOPMENT OF THE UPANISHADIC DOCTRINE

The modern theory voiced in some quarters that the Upanishads represent the revolt of the critical minded kshatriya against the ritualistic brahmin, finds little support in the texts themselves. For not only do brahmin teachers outnumber kshatriya teachers in the Upanishads, it was only the brahmins who fully developed the teachings of the Upanishads as presented in the various schools of Vedaanta. A kshatriya teaching brahma vidhya or knowledge of reality to a brahmin, is no argument, since tradition allowed all the three top castes to learn Vedaanta and it is not unusual for a spiritually inclined kshatriya to possess higher knowledge of Brahman than the average brahmin. And again such cases are exceptions and not the norm.

Another modern assertion that the Upanishads are against the sacrificial religion of the Braahmanas is not wholly true. As noted before the Vedas are a whole spiritual package and each section - the hymns, the sacrifices, the philosophical discussions - have their validity and usefulness at a certain stage. The sacrificial religion served the religious needs of the masses and also helped in the purification of oneself. At the householder stage they're the main source of revenue for the brahmin. No orthodox thinker would object to that, which has so much social, spiritual and religious utility. So the Upanishads are not against the sacrifices per se, but only against their ultimate validity i.e., their ability or rather the lack of it, to effect liberation. While the sacrificial religion is to be practiced in the householder stage, when one moves to the forest dweller stage one is supposed to meditate on the symbolism and spiritual value of the sacrifices. During the samnyaasin stage one's life (worldly life with all its attachments) itself is said to be the sacrifice.

SIGNIFICANCE OF THE UPANISHADS

The Upanishads are truly the fount of all Indian philosophy. All the BrAhmanical schools derive their philosophies from the Upanishads and show an almost pathetic eagerness to find common ground between their doctrines and the Upanishads. Not only is Jainism with its duality of matter and Selves influenced by the Upanishads, even the Buddhist doctrines of annata, kshanikavaada, shunyavaada, vijnaanavaada and the two levels of reality are all derived from the Upanishads.

Numerous scholars have felt compelled down the ages to compose their own commentaries or sub-commentaries on the Upanishads. The commentaries of Shankaracharya are the most ancient available ones, and also the most popular. These are written from an Advaita Vedaanta perspective. The commentaries of Purnapraajna Anandatirtha (also called Madhvacharya) are written from a Dvaita Vedaanta perspective, whereas Rangaramanuja has written his commentaries from a Vishishtadvaita Vedaanta perspective. A partial list of these commentaries in Appendix B will give an idea of how prolific their commentarial tradition has been.

PHILOSOPHY OF THE UPANISHADS

The Upanishads do not represent systematic philosophy. They represent teachings of the sages who experienced or rather became reality (brahma vid brahmaiva bhavati - the knower of Brahman becomes Brahman). The purpose of the Upanishads is not mere intellectual satisfaction, but a practical solution to the ultimate problems of life. It is best expressed in the dialogue between Yama and Nachiketas in the Katha Upanishad. Nachiketas, a braahmana boy questions Yama (the God of Death) as to what happens to one's self after death. Does one exist or does he not, then? Yama tries to dissuade the boy from seeking an answer to a question, which even Gods find difficult to understand. Instead he offers a wide array of earthly comforts : long life, wealth, gold, elephants, horses, land, beautiful women etc. Nachiketas turns them down saying that all these are transient and only serve to wear out the senses of men. And when one has seen him i.e., Yama or death, how could anybody enjoy these things of sense? And having understood the transience of objects of sense and the implicit suffering contained in them, who would wish for a longer life?

As all phenomena are transient in nature worldly life ultimately leads to disappointment and suffering. Death puts an end to all our hopes and ridicules our achievements in life. To be born again is only to go through the same grind. So the end of suffering is not to be born at all and to become immortal. This according to the Upanishads can be achieved when we know the true nature of our Self (Atman).

The teaching of the Upanishads can be best understood under the following three categories :

1. the Self or essence of man - Atman
2. the Self or essence of the world - Brahman
3. the relation between Atman and Brahman

ATMAN

We find a clear exposition of the doctrine of the Atman and the practical path leading to it in the dialogue between the sage Prajaapathi and Indra in the Chaandogya Upanishad. Indra, the king of Gods and Virochana, the king of demons both approached Prajaapathi to learn the doctrine of the Self. Prajaapathi first teaches them that the Self is unborn, uncreated, eternal, cannot be destroyed and beyond suffering. Then he identifies the Self with the body. While Virochana returns home satisfied, Indra is not convinced. How can the immortal Self be the body, which is prone to change, decay and destruction? So he approaches Prajaapathi again and tells him of his confusion. Prajaapathi next identifies the Self with the subject of the dream state. Indra is again not convinced. How could the subject of the dream state be the eternal Self? Though devoid of defects of the body, it still experiences emotions in dreams - it is happy, sad, terrified, conscious of pain etc The Self being eternal cannot be subject to such limitations. So again he goes back to Prajaapathi and tells him his doubts. Prajaapathi now tells him that the enjoyer of the deep sleep state is the Self. But Indra is unconvinced by this too, for in deep sleep, there's no conscious or awareness. We neither feel anything, nor know anything, nor will anything. So what good is there in such a state?

When he approaches Prajaapathi again, the sage well pleased with his discriminatory powers says : Dear Indra! The body and the subject of the dream state are not the Self though they exist for the Self. The Self is not an abstract principle of the deep sleep state too. Yet it is something, which persists through these three states or else we would not have the unity of experience through the three states. The body, the senses, the mind, the presentation continuum, the consciousness - are all mere instruments and objects of the Self. Though the Self is the ground for the waking, dream and deep sleep states, it transcends them all. The Self is immortal, self-luminous and self-proved. It is the ultimate subject, which can never become an object and is necessarily presupposed by all knowledge. It is satchitAnanda (sat - existence, chit - knowledge, Ananda - bliss).

But if we are in truth the eternal Atman, why do we not know it?

The Upanishads say that it is due to our ignorance (avidya) that we're not aware of the true nature of ourselves. When ignorance is removed with right knowledge, the Self shines forth in its true nature. In fact, acquisition of spiritual knowledge is the supreme purpose of human existence. Human beings are superior to other forms of life only because they can sufficiently discriminate between the real and the unreal, between the ephemeral and the eternal, between darkness and light. A man who does not strive to make good of this opportunity and remains lost in materialism has, as if, committed suicide. The 3rd verse of Ishavasya Upanishad therefore declares:

"The immutable soul is the real nature of man, and not his mortal frame.
Because the soul endures from one life to the next,
whereas the body changes every moment and perishes with death.
But the materialistic people, enveloped with ignorance, vanity or pride,
deny the very existence of the soul.
They say- 'Only that exists which can be perceived with the senses.
There is nothing beyond, there is no yonder world after death.
Verily, man is but an agglomeration of the elements,
born of the lust of his parents.
We are born with our physical birth, and cease to exist after our death.
Indeed, there is no connection between actions and their fruits.
There no vice or virtue. So eat, drink and be merry.'
Denying their own true essence,
these deluded men have killed their own souls in this very life."

Recourse to Spirituality does not mean that one can forget his worldly duties. The Upanishads stress again and again that 'faith without works is dead." As an example, quote the 2nd verse of the Ishavasya Upanishad:

"Seek not the Truth by abandoning this world
Or by renouncing all your bounden duties.
This is indeed not the path of salvation.
Rather, desire ye to live a full life of a hundred years,
Actively engaged in the selfless perfromance
of your duties and enjoined actions at all times.
Verily, this is the only way enjoined for man's salvation,
And not the opposite.
All actions bear fruit- good or bad.
And these fruits taint his soul, causing him to be reborn!
But the fruits of actions- good or otherwise, don't taint that wise man,
who performs his duties selflessly, as an offering to God,
Just as a lotus leaf is not tainted by water, even though touching it.
But he, who through ignorance, shirks away from his duties,
Merely deludes himself by thinking- 'I am performing any action!'
Aye! no man can desist from action for even a single moment."

If the true Self of man is the Atman or reality, what about matter and the psychological mechanism?

The Upanishads are very clear that Brahman is the origin and the end of the world. It is the material cause of the world and the world is a manifestation of Brahman. Brahman made the world out of itself. The Brahmasukta of Atharveda (Paippalada Shakha) states

"(It is) The Supreme Being (Who) first spread out the mighty powers collected in Him
(It is) The Supreme Being (Who) first spread out the heavenly lights everywhere
Verily, The Supreme Being was born as first Lord of all that exists
Who, then is fit to be this Supreme Being's rival" VIII.9.1

"These Heaven and Earth are Supreme Being,
The seven currents are The Supreme Being
All the Adityas are Supreme Being
(Verily) All the divine beings contemplate upon the Supreme Being." VIII.9.2

In the beginning the world was just Being, one only, without a second.
Then it thought to itself : "Would that I were many. Let me procreate myself".

All this is verily Brahman. Brahman is that from which everything proceeds, that in which everything breathes and that in which everything is finally dissolved.

A theory of evolution is presented in the doctrine of the pancha kosha or the five sheaths in the Taiitriya Upanishad. The lowest level is the annamaya kosha or the plane of matter. Matter is jada or devoid of consciousness and must evolve to life. So the second stage is praanamaya kosha or the plane of life. Vegetables are an example of this kosha. From life evolves perceptual consciousness and thus we have the manomaya kosha or the mental plane. But this is still instinctive consciousness and can be related to that of animals. From instinctive consciousness evolves consciousness, which is self conscious or rational. This is vijnaanamaya koshas or the plane of self-conscious reason. This is the base for moral life and that, which distinguishes man from animal. This is also the plane where the empirical trinity of knower, known and knowledge exist. When the trinity of the knower, known and knowledge become fused in a transcendental unity we have the highest state of evolution - the Anandamaya kosha or non-dual bliss.

So does this evolution mean that the original Brahman is lost?

No. The Upanishads are firm that all such evolution is only in the level of name and form and the original nature of reality is never lost. Analogies equating Brahman to clay in a clay pot or gold in an ornament are used to bring home the point. Though name and form might vary, the essence remains the same. All the stages of evolution are but manifestations of Brahman, which is the soul of all matter and life (sarvabhutaantaraatmaa). It pervades all phenomena and is the inner controller (antaryaamin) of all. "For fear of him fire burns, for fear of him the sun shines and for fear of him the winds, the clouds and death perform their office".

In its very opening verse, the Ishavasya Upanishad reminds us that Brahman is the essence of existence:

"All sentinent and insentinent objects in this ever changing Universe are ephermal and pass away with time.
But the Lord Who is immanent in everything, and controls it in multifarious ways, is Eternal and Imperishable.
Seek to realize this Eternal Truth and do not get entangled in this world.
Enjoy the bounties of Nature, but with a sense of reunuciation.
Do not hanker too much after riches and do not get obsessed with them.
To whom does all this belong? Certainly not to any man,
for we do not bring anything with us, nor do we take anything along.
But He, the Underlying Reality, owns all this, and we are mere guardians of His Divine riches."

When the whole world is the manifestation of Brahman, even the Atman must be Brahman too. The Mahaavaakyas or the great statements of the Upanishads proclaim : "Tat tvam asi - you are that" and "Aham Brahmaasmi - I'm Brahman". Both identify Brahman to one's own self (Atman). But what's the exact nature of their relationship? (This is the focal point of difference between the various schools of Vedaanta).

Are they one and the same? The Advaita school of Vedaanta takes this stand and gives forth a full fledged non-dualistic Absolutism. But if the Atman is eternal and unchanging, what about the changes experienced in the world? According to Advaita Vedaanta, the changes in the world are unreal (mithya) and an illusion (maaya).

Is Brahman and Atman related in the way of part to whole or quality to object? This is the theory of the VisishtAdvaita school of Vedaanta which teaches qualified non-dualism ie the world and the Selves are qualities of Brahman.

Are Brahman and Atman totally different? This cannot be, for it is explicitly taught in the Upanishads that Brahman is the material cause of the world and the world is the manifestation of Brahman. But still the Dvaita school of Vedaanta argues from this angle and presents a scheme where God, Selves and matter are totally distinct and independent realities.

Actually the dualistic interpretation of the Upanishads as presented by the Dvaita school of Vedaanta is not a new phenomenon. The other five Braahmanical schools - Saamkhya, Yoga, Nyaaya, Vaishesika and Purva Mimaamsaa - all claiming to be the correct interpreters of the Upanishads too propound a dualistic view of the universe.

Excerpts from two remarkable passages from the Upanishads are presented below - one from the Brhadaaranyaka Upanishad and the other from the Chaandogya Upanishad. The first is the famous dialogue between the greatest of Indian sages, Yaagnavalkya and his wife Maitreyi regarding the nature of the Atman. The second is the equally famous dialogue between the sage Uddhaalaka Aruni and his son Shvetaketu, where the relationship between Brahman and Atman is taught. The translation is free and not exact.

Brhadaaranyaka Upanishad

Yaagnavalkya had two wives - Maitreyi and Katyaayani. While Maitreyi was a discourser of Brahma Vidhya, Katyaayani possesed only such knowledge as women have. When Yaagnavalkya wished to move on to the forest dweller (vaanaprastha) stage,

"Maitreyi", said Yaagnavalkya, "I'm getting away from this state of householder. So let me make a settlement for you and that Kaatyaayani".

"My Lord", said Maitreyi, "even if the riches of the world were mine, would it make me immortal?

"No", said Yaagnavalkya, "your life will only be like the life of people with plenty of wealth. But there's no hope of immortality through wealth".

Then Maitreyi said, "What shall I do with that by which I do not become immortal? Please, venerable sir, explain to me whatever you know of immortality".

Then Yaagnavalkya said, "You were always dear to me Maitreyi, but now you've become dearer. So as you wish I shall explain it to you. But as I expound, seek to meditate on it".

Then he said, "Verily, not for the sake of the husband is the husband dear, but for the sake of the self is the husband dear. Verily not for the sake of the wife is the wife dear, but for the sake of the self is the wife dear. Verily not for the sake of the sons … wealth … cattle … braahmana … kshatriya … worlds … Gods … Veda … beings … all … is each dear, but for the sake of the self is each dear. Verily Maitreyi, the self is to be seen, to be heard, to be reflected on, to be meditated upon; when verily the self is seen, heard, reflected on and known, then all else is known".

"Braahmanahood deserts him who knows Braahmanahood in anything else than the self. Kshatriyahood deserts him who knows Kshatriyahood in anything else than the self. The worlds desert him … the Gods desert him … the Vedas desert him … the beings desert him … all deserts him who knows all in anything else than the self. This Braahmanahood, this Kshatriyahood, these worlds, these Gods, these Vedas, all these beings, this all are the Self".

"As from a fire kindled with damp fuel different kinds of smoke issues forth, so verily from this great being has been breathed forth the Rg Veda, the Yajur Veda, the Sama Veda, the hymns of the Atharvan and Angirasas, legend, ancient lore, sciences, sacred teachings, verses, aphorisms, explanations, commentaries, sacrifices, oblation, food, drink, this world and the other and all beings".

"As a mass of salt is altogether a mass of taste, without inside or outside, so is the self altogether a mass of intelligence, without inside or outside. Having arisen out of these elements, it vanishes again in them. When it has departed there's no more separate or particular consciousness".

Then Maitreyi said, "Here indeed, venerable sir, you've caused me to reach utter bewilderment. I do not at all understand this Self".

Yaagnavalkya replied, "I do not say anything bewildering. The Self verily is imperishable and of indestructible nature".

"For where there's duality, there one sees another, one smells another, one tastes another, one speaks to another, one hears another, one thinks of another, one touches and knows another. But when everything has become one's own Self, by what and whom should one see, by what and whom should one smell, taste, speak, hear, think, touch and know? By what should we know him by whom all this is known? Indeed by what would one know the knower? The Self is to be described as not this, not this (neti, neti). He is incomprehensible, indestructible, unattached, unfettered. He does not suffer. Thus you have the instruction expounded to you, O Maitreyi. Such verily is life eternal".

Having said this Yaagnavalkya went away into the forest.

Chaandogya Upanishad

"As when the bees collect honey from different trees, mix them up and reduce them to a unity and the essences are not able to discriminate that, "I'm the essence of this tree", "I'm the essence of that tree", even so all creatures though they reach Being in deep sleep, they do not know it".

"That which is the finest essence - that this whole world has as its Self. That is Atman. That is Reality. That art thou (tat tvam asi), Shvetaketu".

"As the various rives which flow into the ocean and become the ocean itself, losing their individuality they know not that, "I'm this river", "I'm that river". Likewise though all creatures here in this world have come forth from Being they do not know that they have come forth from Being".

"That which is the finest essence - that this whole world has as its Self. That is Atman. That is Reality. That art thou (tat tvam asi), Shvetaketu".

"Bring a fruit from that nyagrodha tree there, Shvetaketu".
"Here it is, sir".
"Break it open".
"It is open, sir".
"What do you see there?".
"These fine seeds, sir".
"Break open a seed".
"It is open, sir".
"What do you see now?".
"Nothing, sir".
Then Uddhaalaka said to him, "Verily my dear son, that subtle essence which you do not perceive, verily my dear, from that the great nyagrodha tree exists. Believe me, dear".
"That which is the finest essence - that this whole world has as its Self. That is Atman. That is Reality. That art thou (tat tvam asi), Shvetaketu".

We conclude with a beautiful litany from the Brahmasukta of Atharvaveda (Paippalada Shakha)

"The Supreme Being are the fishermen,
The Suprme Being are the servants,
The Supreme Being indeed are these gamblers.
Man as well as woman originate from the Supreme Being
Women are God and so are men." VIII.9.10

"The Supreme Being is in the highlands, the Supreme Being is in the lowlands, (indeed)
the Supreme Being envelops from all directions.
Trees, mountains and in shrubs or creepers,
(Verily) The Supreme Being abides in these all.
The Earth and the Heavens
The Supreme Being abides in both" VIII.8.11

"These Heaven and Earth are Supreme Being,
The seven currents are The Supreme Being
All the Adityas are Supreme Being
(Verily) All the divine beings contemplate upon the Supreme Being." VIII.9.3

"The Brahamanas speak of (the glories of) the Supreme Being (during the day)
(But) The Supreme Being verily is present (also) in the night.
From The Supreme Being is born the {light} (of the Sun that brightens the day),
By the Supreme Being does fire shine with great splendour (at night). VIII.9.4

"The Supreme Being abides in food producing plants
And it is He who causes the rains (which give life to these plants) to descend.
(Indeed) The Supreme Being is inner animating Soul of all this
As long as the sun shines bright." VIII.9.5

"The Supreme Being is the priest who recites the chants during the ritual,
The Supreme Being is (also) the ritual
As well as the chants being recited with great precision.
From the Supreme Being arises the priest who pours the oblation into the fire
{Within} the Supreme Being {is present} the oblation." VIII.9.6

"The Supreme Being is the fire altar, brimming with clarified butter,
The Supreme Being are the bulls possessing the beneficient seed,
The Supreme Being are the cows, that yield the oblation going into the ritual fire,
The Supreme Being is he who, seated in the divine chariot, attains the well performed magnificent ritual." VIII.9.7

"By the (will of the) Supreme Being the inert (thing) moves (and thus becomes dynamic)
By the (will of the) Supreme Being does the body unite (with life).
By the (will of) Supreme Being does the outward breath return to the man with great trembling." VIII.9.8

Appendix 1

I. Shakala Charana of Rigveda

1. Aitreya Upanishad (2nd Aranyaka of the Aitreya Aranyaka).
2. Asyavaamiya Sukta (Rigveda 1,164,1-64)
3. Purusha Sukta (Rigveda X, 90)
4. Nasadiya Sukta (Rigveda X, 129)
5. Hiranyagarbha Sukta (Rigveda X,121,1-10)
6. Vac Sukta (Rigveda)
7. Mudgala Upanishad of Mudgala Shakha
8. Galava Upanishad of Galava Shakha

1. Bashkalamantra Upanishad

1. Bavrucha Upanishad

1. Kaushitaki Brahamana Upanishad in the Shankhayana Aranyaka
2. Samhita Upanishad in the Shankhayana Aranyaka

1. Taittiriya Upanishad (Taittiriya Aranyaka prapathaka VII-IX)
2. Yajniki or Mahanarayana Upanishad (Taittiriya Aranyaka prapathaka X)

1. Kathakamantra or Kathaka or Katha Upanishad
2. Kathashruti Upanishad
3. Kanthashruti Upanishad
4. Shivasamkalpa Brahamana
5. Katha Shiksha Upanishad

1. Maitrayaniya Upanishad or Maitrayainiya Aranyaka or Brihadaranyaka of Maitrayaniya Shakha (the Charaka Aranyaka manuscript is almost identical to this text)
2. Chhagaleya Upanishad of the Chhagaleya Shakha
3. Shvetashvatara Upanishad of the Shvetashvatara Shakha

1. Vajasneyi Samhita Upanishad or Isha or Ishavasya Upanishad (Madhyandina and Kanva recensions).
2. Brihadarnyaka Upanishad (Madhyandina and Kanva recensions).
3. Agnirahasya section in book X of Shatapath Brahman
4. Jabala Upanishad of Jabala Shakha
5. Subala Upanishad
6. Mandala Brahamana Upanishad
7. Tadeva Upanishad (in Yajurveda Samhita)
8. Rudrasukta (In Yajurveda Samhita)

1. Jaiminiya Braahmana Upanishad or Talavakara Aranyaka
2. Kena Upanishad in the Talavakara Aranyaka
3. Shatyayana Gayatri Upanishad in the Talavakara Aranyaka
4. Pranagnihotra in the initial sections of the Jaiminiya Brahman

1. Chhandogya Upanishad or Tandya Rahasya Upanishad

1. Atharvana Upanishad or Mantra Upanishad of Atharvaveda or Mundaka Upanishad
2. Pranava Upanishad ( in Gopatha Braahmana)
3. Skambha Sukta
4. Ucchishta Sukta
5. Prana Sukta
6. Gayatri Upanishad (Gopatha Brahamana I, 32-33)
7. Brahma Sukta

1. Prashna Upanishad
2. Brahma Upanishad
3. Garbha Upanishad
4. Samhita Upanishad or Brahma Sukta (Paippalada Atharvaveda VIII, 9, 1-12)

1. Chulika Upanishad
2. Mandukya Upanishad
3. Brahmabindu Upanishad
4. Nadabindu Upanishad
5. Dhyanabindu Upanishad
6. Amritabindu Upanishad
7. Tejobindu Upanishad
8. Atharvashiras Upanishad
9. Atharvashikha Upanishad
10. Kaivalya Upanishad

1. Shaunaka Upanishad
2. Arsheya Upanishad

Appendix B

Prasnopanishad

1. Bhasya of Sri Samkaracharya
2. Tika of Anandajnaana: This is merely a subcommentary on # 1 above
3. Bhasya of Sri Madhvacharya
4. Bhasya of Jayathirtha: This is a subcommentary on # 3 above
5. Aloka of Sri Vijnaana Bhiksu
6. Vivarana of Narayanendra Saravati, the disciple of Jnanendra and the grand-disciple of Kaivalyendra Sarasvati: This is a sub-commentary on # 1 above
7. Bhasya of Rangaramanuja Muni
8. Dipika of Narayana Bhatta, son of Ratnakara Bhatta
9. Dipika of Samkarananda Bhagvat, the disciple of Acharya Anandatma
10. Commentary by Damodara Sastri
11. Upanisadabrahmayogin (Paramadvaita): Manuscript at Central Library at Baroda
12. Hindi Bhasya of Damodara Satavalekara

1. Samkaracarya (Advaita)
2. Bhaskara Bhatta: Manuscripts mentioned by Oppert. It is clear which Bhatta Bhaskara this is since several scholars of this name are known in Hindu history
3. Anubhutisvarupacarya: A sub-commentary on # 1 above
4. Madhvacarya (Dvaita)
5. Anandagiri: A sub-commentary on # 1 above
6. Jayatirtha: A subcommentary on # 4 above
7. Aloka of Vijnaana Bhiksu
8. Rangaramanuja (Visistadvaita)
9. Dipika of Narayana Bhatta, son of Ratnakara Bhatta
10. Nrsimhacaryya Chhalari (Dvaita)
11. Nigudhartha Prakasika of Damodara Sastri
12. Dipika of Samkarananda Bhagavat, the disciple of Acharya Anandatma
13. Upanisadabrahmayogin (Paramadvaita): Manuscript at Central Library at Baroda
14. Damodara Satavalekara

1. Karikas if Gaudapadacharya
2. Bhasya of Sri Samkaracharya on the Upanishad and the Karikas
3. Bhasya of Sri Madhvacharya
4. Tika of Anandagiri (on #2 above)
5. Tika of Jayatirtha (on # 3 above)
6. Aloka of Sri Vijnaana Bhiksu
7. Bhasya of Rangaramanujamuni
8. Dipika of Samkarananda Bhagvat, the disciple of Acharya Anandatma
9. Dipika of Narayana Bhatta, son of Ratnakara Bhatta

Also called Atmashatakopanishad because it is often divided into 6 khandas in traditional commentaries.
1. Samkaracharya. Only the commentary on Aranyaka 3.4-6 is normally printed. Manuscripts at CalcuttA
2. Bhasya of Sri Madhvacharya
3. Tika by Anandagiri on # 1 above
4. Tika of Anantandagiri
5. Tika on # 2 above by Vyasatirtha (Visistadvaita)
6. Sayanacharya
7. Tika of Visvesvara
8. Bhasya Tippana by Jnaanamrta Yati, the disciple of Uttamamrta
9. Vivarana on Samkaracarya's comment on A.A. 3.4-6 by Abhinava Narayanendra Sarasvati, the disciple of Jnanendra Sarasvati and grand disciple of Kaivalyendra Sarasvati (Manuscript at RAS, Calcutta #214)
10. Nigudarthaprakasanam of Damodara Sastri

1. Vakyakara Braahmanandin: A brief comment, called the 'Vakya'. Lost but citations in the works of later Vedaantins are seen.
2. Bhasyakara Dramidacarya: A commentary on # 1 above: The work is lost but citations in the works of later Vedaantins are seen.
3. Samkaracarya (Advaita):
4. Bhaskara Bhatta (Bhedabheda): Lost, but profuse citations in the Tippana of Narendra Puri (# 5 below)
5. Narendra Puri: A brief comment ('Tippana') on # 3 above
6. Madhvacarya (Dvaita)
7. Anandagiri: A gloss on # 3 above)
8. Sayanacarya (Advaita): It has been published
9. Jayatirtha: A sub-commentary on # 6 above
10. Rangaramanuja (Visistadvaita)
11. Raghavendra Yati (Dvaita)
12. Mitaksara of Nityananda Asrama (Advaita Vedaanta)
13. Nigudhartha Prakasana of Damodara Sastri
14. Damodara Satavalekara
15. Pundit Shiva Shankara Kavyatirtha

1. Bhavatrata (unkown): Portion of a commentary on the entire Talavakara Aranyaka - manuscript preserved at the Vishvesvaranand Vedic Research Institute at Hoshiarpur, India
2. Samkaracarya (Advaita): Wrote two commentaries- the more extensive 'Padabhasya' and the shorter 'Vakyabhasya'.
3. Anandagiri: Sub-commentaries on # 2 above
4. Madhvacarya (Dvaita)
5. Jayatirtha: A sub-commentary on # 4 above
6. Rangaramanuja (Visistadvaita)
7. Dipika of Samkarananda Bhagvat
8. Nigudhartha Prakasika by Damodara Sastri
9. Upanisadbrahmayogin (Paramadvaita): Manuscript preserved at Central Library at Baroda
10. Damodara Satavalekara

1. Bhartrprapanca (Bhedabheda)
2. Samkaracarya (Advaita)
3. Anandagiri: Sub-commentary on # 2 above
4. Gopalayatindra or Gopalayogi: Sub-commentary on # 2 above
5. Rangaramanuja (Visistadvaita)
6. Madhvacarya (Dvaita)
7. Jayatirtha: Sub-ommentary on # 6 above
8. Aloka of Vijnaana Bhiksu
9. Nigudhartha Prakasika by Damodara Sastri
10. Upanisadbrahmayogin -manuscript in Central Library- Baroda (Paramadvaita)
11. Damodara Satavalekara (Vaidik): In Hindi

1. Samkaracarya (Advaita): This and all others subsequently are on the Kanva version of the text
2. Suresvaracharya: A voluminous commentary in approximately 12,000 verses. It is a Varttika
3. Bhasya of Madhvacharya
4. Anandagiri's commentary on the Varttika of Sri Suresvaracharya
5. Anandagiri's independent commentary on the Upanishad called 'Nyayamrita'
6. Tippana on # 3 by Jayatirtha
7. Aloka of Sri Vijnaana Bhiksu
8. Bhasya of Rangaramanuja Muni
9. Bhasya of Upanishad Brahmayogin
10. Hindi Bhasya by Pt. Satavalekara

1. Bhartrprapanca (Bhedabheda Vedaanta: Was probably on Madhyandina recension of Yajurveda. No longer extant. Extensive quotations are found in the Bhasyas of Sri Samkaracharya, Sri Suresvacharya, Anandagiri and Anandapurna Muni
2. Samkaracarya (Advaita Vedaanta): This is on Kanva recension of Yajurveda
3. Uvata (Vaidik commentary): This is a part of the commentary on the entire Yajurveda (Madhyandina recension)
4. Kuranarayana (Visistadvaita Vedaanta)
5. Tippana of Narendra Puri
6. Madhvacarya (Dvaita Vedaanta)
7. Tippana by Anubhutisvarupacharya (manuscript at Bikaner)
8. Anandagiri: Sub-commentary on # 2 above
9. Venkatanatha (Visistadvaita Vedaanta)
10. Sayanacarya (Advaita Vedaanta): Manuscript at Central Library at Baroda
11. Vijnaanabhiksu (Samkhya-Vedaanta)
12. Jayatirtha: Sub-commentary on # 7 above
13. Anantabhatta: part of his commentary on Kanva Yajurveda Samhita
14. Mahidhara: Vaidik commentary. This is a part of the commentary on the entire Yajurveda (Madhyandina Sakha) Samhita.
15. Chintamani by Sadananda
16. Bhashya of Appaya Dikshita
17. Dipika of Raghavendra Yati (Dvaita Vedaanta)
18. Dipika of Samkarananda, the disciple of Acharya Anandatma, on #2 above
19. Dipika of Balakrishnananda
20. Bhashya by Kika, the son of Narayana (date unknown)
21. Bhashya by Gopalananda, disciple of Sahajananda (date unknown)
22. Chandrika by Hridayarama (date unknown)
23. Tippana by Jnaanananda (date unknown)
24. Manuprabha commentary by Amaradasa (date unknown)
25. Viveka by Sridharananda (date unknown)
26. Upanisadbrahmayogin (Paramadvaita Vedaanta): Manuscript at Central Library, Baroda
27. Commentary by Damodararya (date unknown)
28. Commentary by Narasimha (date unknown)
29. Vrtti by Devendranatha Thakur (1862)
30. Commentary by Gangadhara Kaviratna Kaviraja
31. Vimala by Taracharana Tarkaratna (1880)
32. Vyakhya and Rahasyavrtti by Ramachandra Pandit, son of Siddheshvara
33. Dayanand Saraswati: Vaidik commentary. Part of the commentary on the entire Yajurveda (Madhyanadina Sakha) Samhita
34. Vivarana by Swami Prakashananda
35. Commentary by Gobhila published by Suddha Dharma Mandala
36. Damodara Satavalekara: Vaidik commentary. In Hindi
37. Rajvira Shastri- Hindi gloss comparing the commentaries of Shankaracharya and Dayanada Saraswati

1. Bhartrprapancha
2. Disciples of Bhartraprapancha: In his Varttika, Suresvara refers to interpretations of # 1 by disciples of Bhartrprapanca
3. Hariswami: Portion of a commentary on the entire Satapatha Brahman. The relevant portion is lost
4. Mukhyartha Prakasika of Dviveda Ganga, the son of Narayana
5. Vasudeva Brahma
6. Nilakantha: The author Nilakantha was the son of Ranganatha Saiva and Laksmi. His teachers were Kasinatha and Sridhara. He referred to the previous commentaries by Sri Samkaracharya and Sri Suresvaracharya on the Kanva version but omitted to comment on the first two Braahmanas although they were commented upon by Sri Samkaracharya. Nilakantha gives a reason for this omission and states that these two Braahmanas strictly belong to Asvamedha Karmakaanda and are dealt with in the 10th prapathaka of Madhyandina Satapatha Braahmana. Therefore, they should not be dealt with in a commentary on the Upanisad.
7. Mitaksara of Nityanandasrama, the disciple of Purusottamasrama

1. Bhasya of Rangaramanuja Muni
2. Dipika of Narayana Bhatta, son of Ratnakara Bhatta
3. Dipika of Narayanashramin
4. Dipika of Shankarananda
5. Commentary of Mukunda
6. Vivarana of Upanishadbrahmayogin

1. Commentary ascribed to Sri Samkaracharya: considered spurious by many scholars
2. Aloka of Vijnaana Bhiksu
3. Commentary by Vijnaanatman, the disciple of Jnanottama

1. Bhatta Bhaskara
2. Sayanacharya
3. Bhasya of Kesava, a disciple of Sri Madhvacharya: It follows the Andhrapatha of the text.
4. Dipika of Narayana Bhatta, son of Ratnakara Bhatta