Taittirīya Upaniṣad · 1
भृगुर्वै वारुणिः । वरुणं पितरमुपससार । अधीहि भगवो ब्रह्मेति । तस्मा एतत्प्रोवाच । अन्नं प्राणं चक्षुः श्रोत्रं मनो वाचमिति । तं होवाच । यतो वा इमानि भूतानि जायन्ते । येन जातानि जीवन्ति । यत्प्रयन्त्यभिसंविशन्ति । तद्विजिज्ञासस्व । तद्ब्रह्मेति
bhṛgur vai vāruṇiḥ | varuṇaṃ pitaram upasasāra | adhīhi bhagavo brahmeti | tasmā etat provāca | annaṃ prāṇaṃ cakṣuḥ śrotraṃ mano vācam iti | taṃ hovāca | yato vā imāni bhūtāni jāyante | yena jātāni jīvanti | yat prayanty abhisaṃviśanti | tad vijijñāsasva | tad brahmeti
Bhṛgu, the son of Varuṇa, approached Varuṇa his father, saying: ‘Lord, teach me Brahman’. To him he said this: Food, life, sight, hearing, mind, speech. To him he said: From which these beings are born; by which, having been born, they live; into which, upon departing, they enter — that investigate; that is Brahman.
The Bhṛguvallī begins with the famous dialogue between Varuṇa and his son Bhṛgu. Bhṛgu seeks the knowledge of Brahman, and Varuṇa responds indirectly — first enumerating the gateways (food, life, senses, mind, speech) through which Brahman can be known, and then providing the fundamental definition of Brahman.
The definition of Brahman here is triadic:
- Yato jāyante — That from which (they are) born (origin)
- Yena jīvanti — That by which they live (sustenance)
- Yat prayanti abhisaṃviśanti — That into which they enter upon departing (dissolution)
This triple characteristic identifies Brahman as the material and efficient cause of the universe — as the ocean is the cause of waves, their sustenance and their dissolution.
The verb vijijñāsasva (investigate) indicates that the knowledge of Brahman requires active investigation — not merely faith, but inquiry through the method of anvaya-vyatireka (concordance and discordance): identifying what remains constant while everything else changes.