Mahāvākyas literally means “The Great Sayings” of the Upanishads

The post-Śaṅkara writers on Advaita Vedānta have mentioned four sentences taken from four Upaniṣads and belonging to the four Vedas which teach the unity of the ātman and Brahman as four ‘mahāvākyas’ or great sentences. They are:

Mahāvākyas

  • Tat Tvam Asi (तत् त्वम् असि) - traditionally rendered as “That Thou Art” (that you are), (Chandogya Upanishad 6.8.7 of the Sama Veda, with tat in Ch.U.6.8.7 referring to sat, “the Existent”); correctly translated as “That’s how [thus] you are,” with tat in Ch.U.6.12.3 referring to “the very nature of all existence as permeated by [the finest essence]”

  • Aham Brahman Asmi (अहम् ब्रह्मास्मि) - “I am Brahman”, or “I am Divine” (Brihadaranyaka Upanishad 1.4.10 of the Yajur Veda)

  • Prajnanam Brahma (प्रज्ञानम् ब्रह्म) - “Prajñāna is Brahman”, or “Brahman is Prajñāna” (Aitareya Upanishad 3.3 of the Rig Veda)

  • Ayam Atma Brahma (अयम् आत्मा ब्रह्म) - “This Self (Atman) is Brahman” (Mandukya Upanishad 1.2 of the Atharva Veda)

Those statements are interpreted as supporting the insight that the individual self (jiva) which appears as a separate existence, is in essence (atman) part and manifestation of the whole (Brahman).O

Sources

## Chandogya Upanishad 6.8.7 - Tat Tvam Asi (तत् त्वम् असि)

स य एषोऽणिमैतदात्म्यमिदं सर्वं तत्सत्यं स आत्मा तत्त्वमसि श्वेतकेतो इति भूय एव मा भगवान्विज्ञापयत्विति तथा
सोम्येति होवाच ॥ ६.८.७ ॥
॥ इति अष्टमः खण्डः ॥
sa ya eṣo'ṇimaitadātmyamidaṃ sarvaṃ tatsatyaṃ sa ātmā tattvamasi śvetaketo iti bhūya eva mā
bhagavānvijñāpayatviti tathā somyeti hovāca || 6.8.7 ||
|| iti aṣṭamaḥ khaṇḍaḥ ||
  1. ‘That which is the subtlest of all is the Self of all this. It is the Truth. It is the Self. That thou art, O Śvetaketu.’ [Śvetaketu then said,] ‘Sir, please explain this to me again.’ ‘Yes, Somya, I will explain again,’ replied his father.

Saḥ yaḥ, that which; eṣaḥ, this; aṇimā, the subtlest of all; idam sarvam aitadātmyam, the Self of all this; tat satyam, that is the Truth; saḥ ātmā, that is the Self; tat, that; tvam, you; asi, are; śvetaketo iti, O Śvetaketu; bhagavān, sir; bhūyaḥ eva, again; mā, to me; vijñāpayatu iti, will you please explain; tathā, so be it; somya iti, O Somya; ha uvāca, he [the father] said. Iti aṣṭamaḥ khaṇḍaḥ, here ends the eighth section.

Brihadaranyaka Upanishad 1.4.10 - Aham Brahman Asmi (अहम् ब्रह्मास्मि)

ब्रह्म वा इदमग्र आसीत्, तदात्मानमेवावेत्, अहम् ब्रह्मास्मीति । तस्मात्तत्सर्वमभवत्; तद्यो यो देवानाम्
प्रत्यबुभ्यत स एव तदभवत्, तथार्षीणाम्, तथा मनुष्याणाम्; तद्धैतत्पश्यन्नृषिर्वामदेवः प्रतिपेदे, अहम् मनुरभवं
सूर्यश्चेति । तदिदमप्येतर्हि य एवं वेद, अहम् ब्रह्मास्मीति, स इदं सर्वम् भवति, तस्य ह न देवाश्चनाभूत्या ईशते,
आत्मा ह्येषां स भवति; अथ योऽन्यां देवतामुपास्ते, अन्योऽसावन्योऽहमस्मीति, न स वेद, यथा पशुरेवम् स देवानाम् । यथा ह
वै बहवः पशवो मनुष्यम् भुञ्ज्युः, एवमेकैकः पुरुषो देवान् भुनक्ति; एकस्मिन्नेव पशावादीयमानेऽप्रियम् भवति, किंउ
बहुषु? तस्मादेषाम् तन्न प्रियम् यदेतन्मनुष्याविद्युः ॥ १० ॥
brahma vā idamagra āsīt, tadātmānamevāvet, aham brahmāsmīti | 
tasmāttatsarvamabhavat; tadyo yo devānām pratyabubhyata sa eva tadabhavat, tathārṣīṇām, tathā manuṣyāṇām;
taddhaitatpaśyannṛṣirvāmadevaḥ pratipede, aham manurabhavaṃ sūryaśceti | tadidamapyetarhi ya evaṃ veda, aham
brahmāsmīti, sa idaṃ sarvam bhavati, tasya ha na devāścanābhūtyā īśate, ātmā hyeṣāṃ sa bhavati; atha yo'nyāṃ
devatāmupāste, anyo'sāvanyo'hamasmīti, na sa veda, yathā paśurevam sa devānām | yathā ha vai bahavaḥ paśavo
manuṣyam bhuñjyuḥ, evamekaikaḥ puruṣo devān bhunakti; ekasminneva paśāvādīyamāne'priyam bhavati, kiṃu bahuṣu?
tasmādeṣām tanna priyam yadetanmanuṣyāvidyuḥ || 10 ||
  1. This (self) was indeed brahman in the beginning. It knew only I(?) as. ‘I am Brahmaṇ.’ Therefore It became all. And whoever among the gods knew It all became That; and the same with sages and so on. The sage Vāmadeva, while realising thi(?)elf) as That, knew, ‘I was Manu, and the s(?)’ And to this day whoever in like manner k(?)s It as, ‘I am Brahman,’ becomes all this (?)verse). Even the gods cannot prevail against(?) him, for he becomes their self. While (?)who worships another go(?)hinking, ‘He is one, and I am another,’ d(?) not know. He is like an animal to the god(?)As many animals serve a man, so does each (?)n serve the gods. Even if one animal is t(?)n away, it causes anguish, what should one; (?) of many animals? Therefore it is not liked(?) them that men should know this.

Aitareya Upanishad 3.3 - Prajnanam Brahma (प्रज्ञानम् ब्रह्म)

एष ब्रह्मैष इन्द्र एष प्रजापतिरेते सर्वे देवा इमानि च
पञ्चमहाभूतानि पृथिवी वायुराकाश आपो
ज्योतींषीत्येतानीमानि च क्षुद्रमिश्राणीव ।
बीजानीतराणि चेतराणि चाण्डजानि च जारुजानि च स्वेदजानि चोद्भिज्जानि
चाश्वा गावः पुरुषा हस्तिनो यत्किञ्चेदं प्राणि जङ्गमं च पतत्रि
च यच्च स्थावरं सर्वं तत्प्रज्ञानेत्रं प्रज्ञाने प्रतिष्ठितं
प्रज्ञानेत्रो लोकः प्रज्ञा प्रतिष्ठा प्रज्ञानं ब्रह्म ॥ ३॥
eṣa brahmaiṣa indra eṣa prajāpatirete sarve devā imāni ca
pañcamahābhūtāni pṛthivī vāyurākāśa āpo
jyotīṃṣītyetānīmāni ca kṣudramiśrāṇīva .
bījānītarāṇi cetarāṇi cāṇḍajāni ca jārujāni ca svedajāni codbhijjāni
cāśvā gāvaḥ puruṣā hastino yatkiñcedaṃ prāṇi jaṅgamaṃ ca patatri
ca yacca sthāvaraṃ sarvaṃ tatprajñānetraṃ prajñāne pratiṣṭhitaṃ
prajñānetro lokaḥ prajñā pratiṣṭhā prajñānaṃ brahma .. 3..

Mandukya Upanishad 1.2 - Ayam Atma Brahma (अयम् आत्मा ब्रह्म)

सर्वं ह्येतद्ब्रह्म ।
अयमात्मा ब्रह्म ।
सोऽयमात्मा चतुष्पात् ॥ २ ॥
Sarvaṃ Hy-Etad-Brahma.
Ayam-Ātmā Brahma.
So’yam-Ātmā Catuṣpāt.

सर्वं – Sarvaṃ – all हि – Hi – verily एतत् – Etat – this ब्रह्मा – Brahmā – the Absolute अयम् – Ayam – this आत्म – Ātma – the Self ब्रह्मा – Brahmā – the Absolute स – Sa – that अयम् – Ayam – this आत्म – Ātma – the Self चतुष्पात् – Catuṣpāt – four quarters

1.2 All this Universe is the Eternal Brahman, this Self is the Eternal