Sankarananda is a non-dualist medieval philosopher who lived sometime during the 14th century, except that he was one of the teachers of Vidyaranya, who is generally identified by some with Madhava (1350 CE). In his magnum opus, Atma Purana or Upanishad Ratna, Shankarananda summarizes Upanishads in verse form. His other known works include a commentary on the Bhagavad Gita, a gloss on Brahma Sutra and some explanatory texts.
Analyzing the concepts of space, time and matter, he states that Brahman, being homogeneous, eternal, and all-pervading, is not conditioned by these categories. Since words denote objects in relation to genus, quality or action, they cannot primarily convey Brahman, which transcends these relational terms. However, by adhyaropa, i.e., superimposing the world on Brahman, and subsequently negating it (apavada), one can comprehend and teach about Brahman.
Sankarananda explains that avidya (ignorance) veils Brahman and appears as the world. Brahman is the substratum of avidya. While avidya is the transformative material cause of the Universe, Ishvara is the transfigurative material cause. Brahman, the sole Real, is both the material and efficient cause.
He distinguishes between mulavidya (primordial ignorance) and tulavidya (individual ignorance). The Upanishadic phrase “neti, neti” (not this, not this) negates the entire Universe superimposed on Brahman. Beings undergo transmigration on account of their ignorance of their identity with Brahman. Scriptural study and spiritual discipline dispel this ignorance.
Sankarananda sought to generate an interest in knowledge of the Absolute by including in his philosophical treatises stories culled from Upanishads.