 (see, e.g., his commentary on Māṇḍūkya 2. The later Advaita tradition standardized the mind as having this four-fold function). Śaṅkara maintains an Upaniṣadic view that minds are materially constituted by sattva, the subtlest aspect of each primary element. Sattva has a qualitative predominance of lucidity and transparency. It makes the mind akin to the reflective surface of a mirror capable of reflecting light, or like a transparent glass that allows light to pass through while illuminating variations on its surface. Unlike minds, mediums like rocks are inert because of their opacity. They lack enough sattva constitution to be reflective even though they are also fundamentally grounded in consciousness.