Upanishads (उपनिषदः)

Upanishads (Samskrit : उपनिषद्) are the concluding segments, available as a part of Aranyakas. Since they expound the various spiritual and dharmika siddhantas and tattvas that leads a sadhaka to the highest purpose of Moksha and because they are present at the end of the Vedas, they are also referred to as the Vedanta. They do not forbid the rituals or rites prescribed in the Karmakanda but expound that only through Jnana one can attain moksha.

वेदान्तो नामोपनिषत्प्रमाणं तदनुसारीणि। शारीरकसूत्राणि च । vedānto nāmopaniṣatpramāṇaṁ tadanusārīṇi। śārīrakasūtrāṇi ca ।

Sadananda Yogindra, in his Vedantasara says that"Vedanta has the Upanishads for its evidence and includes the Sharira Sutras and other works which corroborate it"

परिचयः ॥ Introduction

The Vedas have been divided into four styles of texts – the Samhitas, the Aranyakas, the Brahmanas and the Upanishads. The subject matter of the whole Veda is divided into Karma-Kanda, Upasana-Kanda and Jnana-Kanda. The Karma-Kanda or Ritualistic section deals with various sacrifices and rituals. The Upasana-Kanda or Worship section deals with various kinds of worship or meditation. The Jnana-Kanda or Knowledge-Section deals with the highest knowledge of Nirguna Brahman. The Samhitas and the Brahmanas constitute Karma-Kanda; the Aranyakas constitute Upasana-Kanda; and the Upanishads constitute Jnana-KandaThe Upanishads along with the Bhagavadgita and Brahmasutras constitute the Prasthana Trayi (प्रस्थानत्रयी) and both the Gita and Brahmasutras are based again on the Upanishads. They are also the foundational sources for all Darshana shastras and including the Jain and Buddhist philosophies.

According to Dr. K. S. Narayanacharya, these are four different modes of expressing the same truths, each as a cross check against others so that misrepresentations are avoided, a method used and valid even today.

Most of the Upanishads are in forms of dialogues between a master and a disciple. In Upanishads, a seeker raises a topic and the enlightened guru satisfies the query aptly and convincingly. The central concepts found in the Upanishads involve the following aspects of Sanatana Dharma

• Brahman (Supreme Being, Ultimate Reality)
• Atman (Self)
• Jiva (Embodiment of Atman)
• Unity of Brahman and Atman (Know that you are Ātman)
• Srshti (Origin of Creation)
• Jnana (Knowledge that Unity and Self are not separate)
• Avidya (Ignorance)
• Moksha (The Paramapurushartha)

The Upanishads speak about the identity of the Supreme Being, the Brahman, the individual Atman, their mutual relationship, the Universe (jagat) and man’s place in it. In short they deal with Jiva, Jagat and Jagadishwara and ultimately the path to mokṣa or mukti. Chronology and dating of Upanishads is not attempted in this article.

व्युत्पत्तिः ॥ Etymology

There are different versions about the meaning of Upanishad as given by many scholars. The term Upaniṣad term consists of उप (upa) and नि (ni) उपसर्ग-s (Upasargas or Prefixes) and सद् धातुः (Sad dhatu) followed by किव्प् प्रत्ययः (Kvip pratyaya as Suffix) used in the sense of विशरणगत्यवसादनेषु । Shri Adi Shankaracharya explains in his commentary on Taittriyopanishad about the meanings of Sad dhatu thus

• विशरण (नाशनम्) to destroy : They destroy the seeds of Avidya causing samsara in a Mumukshu (a sadhaka who wants to attain Moksha), hence this Vidya is called Upanishads

  अविद्यादेः संसारबीजस्य विशरणाद् विनाशनादित्यनेन अर्थयोगेन विद्या उपनिषदुच्यते । avidyādeḥ saṁsārabījasya viśaraṇād vināśanādityanena arthayogena vidyā upaniṣaducyate ।

• गति (प्रपणम् वा विद्यर्थकम्) to obtain or to know : That vidya which leads to or make the sadhaka obtain Brahma, is called Upanishad.

  परं ब्रह्म वा गमयतोति ब्रह्म गमयितृत्वेन योगाद् विद्योपनिषद् । paraṁ brahma vā gamayatoti brahma gamayitr̥tvena yogād vidyopaniṣad ।

• अवसादन (शिथिलर्थकम्) to loosen or to dissolve : Through which cycles of birth, aging etc painful process are loosened or dissolved (that is bondages of samsara are dissolved allowing the sadhaka to attain the Brahma)

  गर्भवासजन्मजराद्युपद्रववृन्दस्य लोकान्तरेपौनपुन्येन प्रवृत्तस्य अवसादपितृत्वेन उपनिषदित्युच्यते । garbhavāsajanmajarādyupadravavr̥ndasya lokāntarepaunapunyena pravr̥ttasya avasādapitr̥tvena upaniṣadityucyate ।

  His also defines the primary meaning of Upanishad as ब्रह्मविद्या (Brahmavidya। Knowledge of Brahma) and secondary meaning as ब्रह्मविद्याप्रतिपादकग्रन्थः (Brahmavidya pratipadaka granth । texts which teach Brahmavidya). Shankaracharya's commentaries of the Kaṭha and Brihadaranyaka Upanishad also support this explanation.

An alternative explanation of the word Upanishad is "to sit near" derived as follows

• नि (ni) उपसर्ग (Upasarga or Prefix) in front of सद् धातुः (Sad dhatu) also means 'to sit'.
• उप (upa) Upasarga is used to mean 'nearness or close to'.
• उपनिषद् term thus means "to sit near"

Thus Upanishad came to mean as ' to sit near the Guru (preceptor) to obtain the 'secret knowledge' or Brahmavidya (as per Shabdakalpadhruma : उपनिषद्यते प्राप्यते ब्रह्म-विद्या अनया इति)

Generally, Upanishads are synonymous with Rahasya (रहस्यम्) or secrecy. Upanishads themselves mention statements such as "इति उपनिषद् इति रहस्यम्" when discussing some important siddhantas. Probably such usages are given to prevent and caution against giving this knowledge to the undeserving.

In the mukhya upanishads, there are many instances of रहस्यम् meaning secret or hidden knowledge especially in Atharvaveda upanishads. Kaushitaki Upanishad for example, contains detailed siddhantas of मनोज्ञानम् and तत्वज्ञानम् (Psychology and metaphysics). Apart from them they also contain मृतकज्ञानम् (siddhantas around death, travel of Atman etc), बालमृत्यु निवारणम् (preventing untimely childhood deaths) शत्रुविनाशार्थ रहस्यम् (secrets about the destruction of enemies) etc. Chandogya Upanishads gives the secrets about the origin of worlds, Jiva, Jagat, Om and their hidden meanings.

Classification of Upanishads

More than 200 Upanishads are known, of which the first dozen or so are the oldest (प्राचीनम्), most important and are referred to as the principal or main (mukhya) Upanishads. The rest of them aid in explaining bhakti or jnana concepts and many are without bhashyas. Some scholars accept 12 Upanishads and some even consider 13 to be the principal Upanishads and some others accept 108 Upanishads given by Muktikopanishad.

There is no fixed list of the Upanishads as newer ones, beyond the Muktika Upanishad list of 108 Upanishads, have continued to be discovered and composed. A collection of Upanishads, namely Upanishad Samgrahah by Pt. J. K. Shastri contains 188 upanishads. Pracheena Upanishads have long been revered in Sanatana Dharma traditions, and many sampradayas have interpreted the concepts of Upanishads to evolve their sampradaya. These "new Upanishads" number in the hundreds, cover diverse range of topics from physiology to renunciation.

Basis for Classification

Many modern and western indology thinkers have put forth their contemplations on the classification of Upanishads and it is based on the following factors

1. the presence or absence of Shankaracharya's bhasyas (Ten for which bhashyas are available are Dasopanishads and the rest describing devatas. Vaishnava, Shaiva, Shakta, Saurya etc)
2. the ancientness of Upanishad based on association with Aranyakas and Brahmanas
3. the ancientness and modernness of the Upanishads based on description of deities and other aspects ( Given by Shri Chintamani Vinayak on Page 256 of Reference )
4. the shanti patha given in each of the Upanishads
5. the ancientness and modernness of the Upanishads having prose or metrical compositions (mostly given by Western Indologists like Dr. Daison)

दशोपनिषदः ॥ Dasopanishads

Muktikopanishad lists the following ten as principal Upanishads which have received attention from Shri Adi Shankaracharya in form of his bhasyas and are considered ancient (प्राचीनम्).

ईश-केन-कठ-प्रश्न-मुण्ड-माण्डूक्य-तित्तिरः । एेतरेयं च छान्दोग्यं बृहदारण्यकं तथा ॥ īśa-kēna-kaṭha-praśna-muṇḍa-māṇḍūkya-tittiraḥ । ēētarēyaṁ ca chāndōgyaṁ br̥hadāraṇyakaṁ tathā ॥

The 10 Mukhya Upanishad on which Adi Shankaracharya commented are:

1. ईशावाश्योपनिषद् ॥ Ishavasya Upanishad (Shukla Yajur Veda)
2. केनोपनिषद् ॥ Kena Upanishad (Sama Veda)
3. कठोपनिषद् ॥ Katha Upanishad (Yajur Veda)
4. प्रश्नोपनिषद् ॥ Prashna Upanishad (Atharva Veda)
5. मुण्डकोपनिषद् ॥ Mundaka Upanishad (Atharva Veda)
6. माण्डूक्योपनिषद् ॥ Mandukya Upanishad (Atharva Veda)
7. तैत्तियोपनिषद् ॥ Taittiriya Upanishad (Yajur Veda)
8. एेतरेयोपनिषद् ॥ Aitareya Upanishad (Rig Veda)
9. छान्दोग्योपनिषद्॥ Chhandogya Upanishad (Sama Veda)
10. बृहदारण्यकोपनिषद् Brhadaranyaka Upanishad (Yajur Veda)

Apart from these ten, कौषीतकि (Kaushitaki) श्वेताश्वतर (Shvetasvatara) and मैत्रायणीय (Maitrayaniya) Upanishads are regarded as ancient since the first two of these three found a mention by Shankaracharya in his Brahmasutra bhashyas along with dashopanishad bhashyas. However, there are no available commentaries on these given by him.

Upanishads as Part of Aranyakas

Many Upanishads are the final or exclusive portions of the Aranyakas or the Brahmanas. But these refer mainly to the dasha upanishads. It may be seen from the table below that some Upanishads not classified in dashopanishads are from Aranyakas. (Ex: Mahanarayaneeya Upanishad, Maitrayaniya Upanishad) while the Atharvana veda associated Upanishads do not have corresponding Brahmanas or Aranyakas as they are unavailable.

Upanishads as part of Aranyakas and Brahmanas

Veda		What part of Brahmana or Aranyaka constitutes Upanishad	Name of Upanishad	Name Comes from	Contents
RigVeda		4th to 6th Adhyayas of 2nd Prapathaka of 2nd Aranyaka of Aitareya Aranyaka (Page 250 of Reference )	एेतरेयोपनिषद् ॥ Aitareya Upanishad	Mahidasa Aitareya composed this Upanishad	Consists of 3 Adhyayas
		3rd to 6th Adhyayas of Shankhyayana Aranyaka (Page 251 of Reference )	कौषीतकि उपनिषद् ॥ Kaushitaki Upanishad	Given by Kaushitaki Rshi	Consists of 4 Adhyayas
Yajurveda	Krishna	7th to 9th Prapathakas of Taittriya Aranyaka (Page 251 of Reference )	तैत्तियोपनिषद् ॥ Taittiriya Upanishad	From source Taittriya Aranyaka	Consists of 3 Vallis or chapters : Shikshavalli, Brahmavalli (Anandavalli) and Bhruguvalli
		10th Prapathaka of Taittriya Aranyaka (also considered as Khila khanda) (Page 251 of Reference )	महानारायणीय उपनिषद् ॥ Mahanarayaniya Upanishad		Consists of collection of passages including both prose and mantras.
		Kathasamhita or Kathavalli (Page 54 of Reference )	कठोपनिषद् ॥ Kathopanishad or काठकोपनिषद् ॥ Kathakopanishad	Comes from the source Katha samhita	2 Adhyayas with 3 vallis each (total 6 vallis) contains 119 mantras.
		Maitrayaniya Aranyaka (Page 251 of Reference )	मैत्रायणीय Maitrayaniya Upanishad	Comes from the source Maitrayaniya Aranyaka	Contains 7 Prapathakas
	Shukla	Last 6 Adhyayas of Shatapatha Brahmana (Page 56 of Reference )	Brhadaranyakopanishad		Contains 6 Adhyayas
		40th Adhyaya of माध्यन्दिन-शतपथ-ब्राह्मणम् ॥ Madhyandina Shatapatabrahmana	ईशावाश्योपनिषद् ॥ Ishavasya Upanishad	The first word of the first mantra ॐ ईशा वास्यमिदँ सर्वं यत्किञ्च जगत्यां जगत् ।	Contains 18 mantras
Samaveda		10th Anuvaka of 4th Adhyaya of जैमिनीय ॥ Jaiminiya (Talavakara तलवकार) Brahmana (Page 253 of Reference )	केनोपनिषद् ॥ Kena Upanishad or Talavakaropanishad	The first word of the first mantra ॐ केनेषितं पतति प्रेषितं मनः	Contains 4 Khandas with 32 mantras in all.
		Last 10 Adhyayas of Chandogyabrahmana of Kauthuma Shakha (Page 55 of Reference )	छान्दोग्योपनिषद्॥ Chhandogya Upanishad		Contains 8 Prapathakas or Adhyayas each having varying number of Kandas and mantras.
Adharvaveda		Associated with Pippalada brahmana (Page 54 of Reference )	प्रश्नोपनिषद् ॥ Prashna Upanishad	Comes from the Prashna or question and answer format seen in this upanishad.	Mostly in prose it has six Prashnas (sections)with 16, 13, 12, 11, 7 and 8 passages respectively.
		Associated with Shaunaka samhita (Page 54 of Reference )	मुण्डकोपनिषद् ॥ Mundaka Upanishad		3 Mundakas (chapters) each containing 2 Khandas with 64 mantras in all.
		Associated with Atharvaveda (Page 55 of Reference )	माण्डूक्योपनिषद् ॥ Mandukya Upanishad	Composed by the son of Mandukya maharshi.	Contains 12 mantras only

Deity and Samkhya Based Classification

Pt. Shri. Chintamani Vinayak Vaidya has assigned the ancientness (प्राचीनता) or modernness (अर्वाचीनता) of Upanishads using the two factors

1. Siddhanta of Anatmarupa Brahma (a supreme power beyond and above deities)
2. Vishnu or Shiva deities are accepted as paradevata (supreme deity) and are praised
3. Principles of Samkhya Siddhanta (Prakriti, Purusha, Gunas-Satva, Rajas and Tamas)

It is proved beyond doubt that the ancient upanishads have described a Supreme Anatmarupa Brahma, above the vaidika deities, who has created regulated and maintained order of the creation. They are thus very ancient and include Aitareya, Isha, Taittriya, Brhadaranyaka, Chandogya, Prashna, Mundaka and Mandukya Upanishads.

Only in the more recent upanishads one can see the older ones in praise of Vishnu as the Supreme Being followed by the more recent one's in praise of Shiva. In this group is classified Kathopanishad where Vishnu is the Supreme Being. Krishna Yajurveda Upanishads are famous for their Shiva and Rudra stutis (Rudra Prashna is a famous stuti) and in this way Shevetashvatara Upanishad which accepts Shiva as paradevata is more recent compared to Kathopanishad. In this series, Maitrayaniya Upanishad which accepts all the Trimurti's (Brahma Vishnu and Shiva) is more recent than the above two mentioned Upanishads.

Katha Upanishad (which has no principles of Samkhya) is ancient as against Shvetashvatara (which expounds principles of Samkhya and its preceptor Kapila Maharshi), further more recent is Maitrayaniya Upanishad where samkhya philosophy along with the description of the gunas is given in detail.

Shanti Patha Based Classification

Some upanishads are not related to any veda, while some are definitely associated with one or the other veda. Based on the Shanti patha that is given in the beginning of the Upanishads the following classification is proposed.(Page 288-289 of Reference )

108 Upanishads Classified Based on Shanti Patha of Each Veda

Veda	Shanti patha	Upanishads
Rigveda	वाङ् मे मनसि प्रतिष्ठिता मनो मे वाचि प्रतिष्ठितमाविरावीर्म एधि ॥ vāṅ mē manasi pratiṣṭhitā manō mē vāci pratiṣṭhitamāvirāvīrma ēdhi ॥	Aitareya, Kaushitaki, Atmaprabodha, Nadabindu, Nirvana, Mudgala, Akshamalika, Tripura, Saubhagya, Bahvrucha Upanishads (10)
Krishna Yajurveda	ॐ सह नाववतु । सह नौ भुनक्तु । सहवीर्यं करवावहै । oṁ saha nāvavatu । saha nau bhunaktu । sahavīryaṁ karavāvahai ।	Kathavalli (commonly referred to as Kathopanishad), Taittriya, Narayana, Brahma, Kaivalya, Shvetasvatara, Garbha, Amrtabindu, Amrtanada, Kalagnirudra, Kshurika, Sarvasara, Shukarahasya, Tejobindu, Dhyanabindu, Brahmavidya, Yogatattva, Dakshinamurty, Katha (different from Kathavalli), Skanda, Shareeraka, Varaha, Yogashikha, Ekakshara, Akshi, Avadhuta, Rudrahrdaya, Yogakundalini, Panchabrahma, Kalisantarana, Pranagnihotra, Sarasvatirahasya Upanishads (32)
Shukla Yajurveda	ॐ पूर्णमदः पूर्णमिदं पूर्णात् पूर्णमुदच्यते । oṁ pūrṇamadaḥ pūrṇamidaṁ pūrṇāt pūrṇamudacyatē ।	Ishavasya, Brhadaranya, Jabala, Subaala, Hamsa, Paramahamsa, Mantrikaniralamba, Tarasara, Trishikhi, Brahmanamandala, Brahmana, Advayataraka, Paingala, Bhikshuka, Turiyateeta, Adhyatma, Muktika, Shatyayani, Yajnavalkya Upanishads (19)
Samaveda	ॐ आप्यायन्तु ममाङ्गानि वाक्प्राणश्चक्षुः श्रोत्रमथो बलमिन्द्रियाणि च सर्वाणि । oṁ āpyāyantu mamāṅgāni vākprāṇaścakṣuḥ śrōtramathō balamindriyāṇi ca sarvāṇi ।...	Kena, Chandogya, Aaruni, Maitrayani, Maitreyi, Vajrasuchi, Yoga, Chudamani, Vasudeva, Sanyasa, Avyakta, Savitri, Rudrakshajabala, Darshanajabali, Kundika, Mahopanishad Upanishads (16)
Adharvanaveda	ॐ भद्रं कर्णेभिः शृणुयाम देवाः भद्रं पष्येमाक्षभिर्यजत्राः । oṁ bhadraṁ karṇēbhiḥ śr̥ṇuyāma dēvāḥ bhadraṁ paṣyēmākṣabhiryajatrāḥ ।	Prashna, Mundaka, Mandukya, Brhadjabala, Nrsimhatapini, Narada parivrajaka, Sitaa, Sharabha, Mahanarayana, Ramarahasya, Ramatapini, Shandilya, Paramahamsa parivrajaka, Annapurna, Surya, Atma, Parambrahma, Pashupata, Tripuratapini, Devi, Bhavana, Bhasmajabala, Ganapati, Mahavakya, Gopalatapini, Krishna, Hayagriva, Garuda, Dattatreya, Atharvashikha, Atharvashiro Upanishads (31)

Authorship

The authorship of most Upanishads is uncertain and unknown. The various philosophical theories in the early Upanishads have been attributed to famous seers such as Yajnavalkya, Uddalaka Aruni, Shvetaketu, Shandilya, Aitareya, Balaki, Pippalada and Sanatkumara. Women, such as Maitreyi and Gargi participated in the dialogues and are also credited in the early Upanishads.

There are exceptions to the anonymous tradition of the Upanishads and other Vedic literature. The Shvetashvatara Upanishad, for example, includes closing credits to Shvetashvatara, and he is considered the author of the Upanishad.

उपनिषद्विषयाः ॥ Vishaya

The main subject of Upanishads is the discussion about Paramatmatattva. There are two kinds of Vidyas : Para (पराविद्या) and Apara (अपराविद्या). Of these Paravidya is supreme and is called Brahmavidya (ब्रह्मविद्या). Upanishads present the detailed discussion about Paravidya. Aparavidya is primarily related to Karmas, hence called Karmavidya (कर्मविद्या). The fruits of Karmavidya are perishable while the results of Brahmavidya are indestructable. Aparavidya may not lead one to Moksha (may lead to svarga and other worlds) but Paravidya always gives Moksha.

Some terms which are well explained in the Upanishads include, Prkriti (प्रकृतिः), Purusha (पुरुषः), Paramatma (परमात्मा), Ishvara (ईश्वरः), Jivatma (जीवात्मा), Maya (माया), Brahman (ब्रह्मन्), Avidya (अविद्या), Indriyas (इन्द्रियानि), etc. From the root cause Prkriti the world came into being. Paramatma is Nitya, Puratana, Shasvata (Eternal) devoid of the cycles of birth and death. The Sharira or body is subjected to death and birth but Atma residing in it continues to exist. Just like butter is evenly distributed in milk so also Paramatma is all-pervading in the world. Just like the sparks arise out of fire so also the beings take shape from the Paramatma. Such aspects which are explained in Upanishads have widely developed in the Darshana shastras.

Based on their content Upanishads can be divided into six categories.

1. Vedanta siddhanta
2. Yoga siddhanta
3. Samkhya siddhanta
4. Vaishnava siddhanta
5. Shaiva siddhanta
6. Shakta siddhanta

वैशिष्ट्यम् ॥ Speciality of Upanishads

Although all Upanishads proclaim that the goal of human life, embroiled in the flow of samsara, is to attain Jnana that leads to Moksha, the ultimate paramapurushartha, each of the upanishads have their own special features about their siddhantas as follows

1. Katha discusses the doubts about post death path of a Jiva
2. Shvetasvatara says Jagat and Paramatma are Maya.
3. Brhadaranyaka gives the paths to higher worlds
4. Mundakopanishad stressed the fact that the whole Universe is nothing but Parabrahma
5. Isavasya defines that a Jnani is one who sees Self and Paramatma pervading the world.
6. Taittriyopanishad proclaims that Brahmajnana leads to Moksha.
7. Chandogyopanishad gives the outline of how janmas (births) happen and paths to reach Brahmaloka.
8. Prashnopanishad logically answers the questions regarding the nature of Atma.
9. Mandukya upanishad proclaims Atman to be Brahman
10. Aitareya upanishad establishes the characteristics of Brahma

The Upanishads include sections on certain siddhantas that have been the very foundation of Sanatana Dharma. For example, the Chandogya Upanishad includes one of the earliest known declaration of Ahimsa (non-violence) as an ethical precept. Discussion of other ethical premises such as Damah (temperance, self-restraint), Satya (truthfulness), Dāna (charity), Ārjava (non-hypocrisy), Daya (compassion) and others are found in the oldest Upanishads and many later Upanishads. Similarly, the Karma doctrine is presented in the Brihadaranyaka Upanishad, which is the oldest Upanishad.

एकं सत् The One Existence

Worship of the nature and devatas such as the Agni, Aditya, Indra, Rudra, Visnu, Brahma and others becomes internalized in the Upanishads to the meditation on the supreme, immortal and formless Brahman-Atman. The many names of devatas with forms and weapons gradually merged into defining a One Existence, a supreme being called now as Paramatma, Brahman etc.

एकं सद्विप्रा बहुधा वदन्ति (Rig. Veda. 1.164.46)

Devatas who held positions in the outer worlds are now declared to be everywhere, even as the innermost being of each human being and within every other living creature.

एकमेवाद्वितीयं ब्रह्म (Chand. Upan. 6.2.1)

What was One reality or ekam satofthe Vedas now becomes the ekam eva advitiyam brahma or "the one and only and sans a second" in the Upanishads. Discussion of Brahman-Atman and Self-realization develops in the Upanishads as the means to moksha (liberation, freedom in this life or after-life). Worship which was primarily of the nature and natural elements (like fire, clouds and rains, air) with deities having a form and qualities called Saguna Brahman transformed to worship of "Tat" (That) without attributes, qualities, beyond name and form called as Nirguna Brahman. The qualities or the nature of Nirguna Brahma includes Infinite, Absolute, Eternal, Changeless, the All

Advaita : Brahman sans second

Brahman and Atman are two concepts that are unique to Indian knowledge systems which are highly developed in the Upanishads. The word Brahman is used to represent the all pervading, ultimate reality without a second. The concept that brahman and jagat (world) are completely distinct from each other is dismissed and the tattva is explained. For example, Chandogya Upanishad describes the unity of Jiva and Brahman, in the form of conversation between Uddalaka and Shvetaketu. Kathopanishad says

यदेवेह तदमुत्र यदमुत्र तदन्विह । मृत्योः स मृत्युमाप्नोति य इह नानेव पश्यति ॥ १० ॥

मनसैवेदमाप्तव्यं नेह नानाऽस्ति किंचन । मृत्योः स मृत्युं गच्छति य इह नानेव पश्यति ॥ ११ ॥ (Kath. Upan. 2.1.11)

Summary : The entity that exists in all beings from Brahma down to immovable and appears as non- Brahman owing to limiting factors (Jiva) is different from Supreme Brahman is subject to birth and death. What indeed is here, is there and what is there is here. He who sees as though there is difference between the two, goes from death to death. This is to be attained through the Manas only. There is no diversity between the Self and Supreme Brahman.

Brhdaranyaka Upanishad also lays emphasis of the Unity of Jiva and Brahman (2.4.6-9). In Yajnavalkya and Maitreyi Samvada, the very nature of Atman is defined. All the brahmanas, kshatriyas, the whole world, the countless devatas and all beings are the form of Atman only.

That Brahman is the basis of the whole universe (Adhishtata) is emphasized in the Taittriya Upanishad. In the Mandukya Upanishad is mentioned, the first time in the history of thought, the distinction between the Brahman and Isvara. Isvara is like a supreme devata in relation to the universe and viewed through human perspective, whereas Brahman is Supreme or Absolute, as He is in Himself, viewed independently. In later Vedantic literature the two are often spoken of as Saguna Brahman and Nirguna Brahman. That is, the same Brahman is viewed from two different standpoints--the relative standpoint and the independent standpoint.

Mundakopanishad, says Brahman is "That which cannot be seen or grasped, which has neither origin nor properties, which has neither eyes nor ears, neither hands nor feet, which is eternal, all-pervading, omnipresent 'and extremely subtle, Imperishable which the rshis regard as the origin of all beings."

Atman

The Atman is individual self (soul). Brahman is the material, efficient, formal and final cause of all that exists. It is the pervasive, genderless, infinite, eternal truth and bliss which does not change, yet is the cause of all changes.^[53][58] Brahman is "the infinite source, fabric, core and destiny of all existence, both manifested and unmanifested, the formless infinite substratum and from which the universe has grown".

The word Atman means the inner self, the soul, the immortal spirit in an individual, and all living beings including animals and trees. These texts state that the inmost core of every person is not the body, nor the mind, nor the ego, but Atman – "Soul" or "Self".^[62] Atman is the spiritual essence in all creatures, their real innermost essential being.^[63][64] It is eternal, it is ageless. Atman is that which one is at the deepest level of one's existence.

Atman is the predominantly discussed topic in the Upanishads, but they express two distinct, somewhat divergent themes. Some state that Brahman (Highest Reality, Universal Principle, Being-Consciousness-Bliss) is identical with Atman, while others state Atman is part of Brahman but not identical.^[65][66] This ancient debate flowered into various dual, non-dual theories in Hinduism.

The idea put forth by the Upanishadic seers that Atman and Brahman are One and the same is one of the greatest contributions made to the thought of the world.

Manas

Manas is also called as Prajna, Chitta, Samkalpa which has some vritti or state of existence. The thinking nature of man has been understood as the very essence of human beings since ancient times in India. Serious searches for unravelling the mystery of mind and its impacts on life proved decisive in deepening the philosophical thoughts of human race making definite impacts upon the socio-cultural standards of life. Studies of mind have contributed much in the fields of arts and science. It is a matter of fact that all philosophical thoughts and knowledge systems in India spring out explicitly or implicitly from the Vedas. The Upaniṣads being an integral part of Vedas represent the philosophical zenith of the Vedic thoughts. The discussions on mind also are dense and deep in the Upanishads.

Aitareya Upanishad describes the origin of cosmic mind along with the origin of universe in a sequential manner.

हृदयं निरभिद्यत हृदयान्मनो मनसश्चन्द्रमा । (Aite. Upan. 1.1.4)

A heart parted open and from it came the mind. from the internal organ, mind, came the Moon.

Thought becomes the power that triggers the process of creation driven by the supposition of a cosmic mind or cosmic intelligent behind creation. While Brhadaranyaka says एतत्सर्वं मन एव " (Brhd. Upan. 1.5.3) All this is the Mind itself". Isavasya refers to Manas in अनेजदेकं मनसो जवीयो । in the context of Atman being faster than the mind. Here the speed is described as a property of mind. Brhdaranyaka further says that Manas is the common ground for all imaginations and decisions. That mind is not consciousness but it is a subtle form of matter like the body is expounded in the Chandogya Upanishad. Anna consumed is sorted in three ways post digestion. The grossest part becomes faeces; the middle component becomes flesh; the subtle ingredient becomes the mind.

Illusion

Main article: Maya (illusion)

Two different types of the non-dual Brahman-Atman are presented in the Upanishads, according to Mahadevan.^[120] The one in which the non-dual Brahman-Atman is the all inclusive ground of the universe and another in which empirical, changing universe is a form of Maya, often translated as "illusion".

The Upanishads describe the universe, and the human experience, as an interplay of Purusha (the eternal, unchanging principles, consciousness) and Prakṛti (the temporary, changing material world, nature).^[67] The former manifests itself as Ātman (Soul, Self), and the latter as Māyā. The Upanishads refer to the knowledge of Atman as "true knowledge" (Vidya), and the knowledge of Maya as "not true knowledge" (Avidya, Nescience, lack of awareness, lack of true knowledge).^[68]

In the Upanishads, Māyā is the perceived changing reality and it co-exists with Brahman which is the hidden true reality.^[71][72] Maya, or "illusion", is an important idea in the Upanishads, because the texts assert that in the human pursuit of blissful and liberating Self-knowledge, it is Maya which obscures, confuses and distracts an individual.^[73][74]

Schools of Vedanta

Main article: Vedanta

The Upanishads form one of the three main sources for all schools of Vedanta, together with the Bhagavad Gita and the Brahmasutras.^[129] Due to the wide variety of philosophical teachings contained in the Upanishads, various interpretations could be grounded on the Upanishads. The schools of Vedānta seek to answer questions about the relation between atman and Brahman, and the relation between Brahman and the world.^[130] The schools of Vedanta are named after the relation they see between atman and Brahman:^[131]

• According to Advaita Vedanta, there is no difference.^[131]
• According to Vishishtadvaita the jīvātman is a part of Brahman, and hence is similar, but not identical.
• According to Dvaita, all individual souls (jīvātmans) and matter as eternal and mutually separate entities.

Other schools of Vedanta include Nimbarka's Dvaitadvaita, Vallabha's Suddhadvaita and Chaitanya's Acintya Bhedabheda.^[132] The philosopher Adi Sankara has provided commentaries on 11 mukhya Upanishads.^[133]

Advaita Vedanta

Advaita literally means non-duality, and it is a monistic system of thought.^[134] It deals with the non-dual nature of Brahman and Atman. Advaita is considered the most influential sub-school of the Vedanta school of Hindu philosophy.^[134] Gaudapada was the first person to expound the basic principles of the Advaita philosophy in a commentary on the conflicting statements of the Upanishads.^[135] Gaudapada's Advaita ideas were further developed by Shankara.^[136][137] King states that Gaudapada's main work, Māṇḍukya Kārikā, is infused with philosophical terminology of Buddhism, and uses Buddhist arguments and analogies.^[138] King also suggests that there are clear differences between Shankara's writings and the Brahmasutra,^[136][137] and many ideas of Shankara are at odds with those in the Upanishads.^[139] Radhakrishnan, on the other hand, suggests that Shankara's views of Advaita were straightforward developments of the Upanishads and the Brahmasutra,^[140] and many ideas of Shankara derive from the Upanishads.^[75]

Shankara in his discussions of the Advaita Vedanta philosophy referred to the early Upanishads to explain the key difference between Hinduism and Buddhism, stating that Hinduism asserts "Atman (Soul, Self) exists", while Buddhism asserts that there is "no Soul, no Self".^[76][77][78]

The Upanishads contain four sentences, the Mahāvākyas (Great Sayings), which were used by Shankara to establish the identity of Atman and Brahman as scriptural truth:

• "Prajñānam brahma" - "Consciousness is Brahman" (Aitareya Upanishad)^[145]
• "Aham brahmāsmi" - "I am Brahman" (Brihadaranyaka Upanishad)^[146]
• "Tat tvam asi" - "That Thou art" (Chandogya Upanishad)^[147]
• "Ayamātmā brahma" - "This Atman is Brahman" (Mandukya Upanishad)^[148]

Although there are a wide variety of philosophical positions propounded in the Upanishads, commentators since Adi Shankara have usually followed him in seeing idealist monism as the dominant force.^{[149][note 9]}

Dvaita

The Dvaita school was founded by Madhvacharya.^[150] Dvaita is regarded as the best philosophic exposition of theism.^[151] Madhva, much like Adi Shankara claims for Advaita, states that his theistic Dvaita Vedanta is grounded in the Upanishads.^[79]

Vishishtadvaita

The third school of Vedanta is the Vishishtadvaita, which was founded by Ramanuja. Ramanuja strenuously refuted Shankara's works.^[153] Visistadvaita is a synthetic philosophy bridging the monistic Advaita and theistic Dvaita systems of Vedanta.^[151] Ramanuja, just as Madhva claims for Dvaita sub-school, states that Vishishtadvaita is grounded in the Upanishads.^[79]