Śaṅkarācārya approached the Upaniṣads as the highest scriptural authority on the nature of reality and the Self, and read them consistently through the lens of Advaita, or non-dualism. For him, the Upaniṣadic revelation culminates in the insight that Brahman, the ultimate reality, is one, without attributes (nirguṇa), pure consciousness, eternal and unchanging. The individual self (ātman) is not a separate entity but is identical with this Brahman, a truth he saw crystallized in mahāvākyas such as “tat tvam asi” and “ahaṁ brahmāsmi.” Whenever the ritual portions of the Veda or more theistic, pluralistic passages seemed to conflict with this non-dual vision, he treated the Upaniṣadic teaching of knowledge as decisive and final.

On this basis, Śaṅkara interpreted the world of multiplicity and individuality as an appearance grounded in avidyā, or ignorance, and articulated through the notion of māyā. The empirical world, the body, and the ego have a kind of dependent or provisional reality, but they do not stand on the same footing as the non-dual Brahman. To clarify this, he distinguished levels of reality: at the highest level (paramārthika), only Brahman truly is; at the empirical level (vyāvahārika), the world and persons function for practical purposes; and at an even more tenuous level (prātibhāsika), dreams and obvious illusions appear. Upaniṣadic descriptions of creation and plurality are thus read as pedagogical, operating within the empirical standpoint, while the identity statements express the ultimate standpoint.

Śaṅkarācārya’s method of reading the Upaniṣads is marked by careful negation and rigorous interpretation. He made extensive use of the “neti, neti” (“not this, not this”) teaching to strip away all limiting adjuncts from the Self, leaving only pure awareness that is identical with Brahman. Statements that speak of difference, qualification, or plurality are taken as provisional teachings suited to seekers at earlier stages, whereas statements of non-duality are treated as the final purport of the texts. Through his bhāṣyas on the principal Upaniṣads, he explained key terms, linked scattered passages into a coherent Advaitic vision, and employed logical analysis to harmonize seemingly contradictory verses without sacrificing the authority of scripture.

For Śaṅkara, liberation (mokṣa) is nothing other than the direct realization of one’s true nature as Brahman, and this realization arises through jñāna, not through ritual action. The Upaniṣads, as he reads them, prescribe a path centered on hearing their teaching, reflecting upon it, and deeply contemplating it until the ignorance that sustains the sense of separation falls away. Rituals and devotional practices retain a place, but only as preparatory disciplines that purify and steady the mind so that it can receive and assimilate the non-dual knowledge. In this way, his interpretation presents the Upaniṣads as a unified, radical proclamation of the oneness of Self and Absolute, with the entire manifold world understood as a meaningful yet ultimately subordinate appearance within that singular reality.