 Śaṅkara’s metaphysical arguments defend Upaniṣadic propositions claiming that existence is “one only, without a second” (ChU 6.2.1). He follows the general Upaniṣadic model that all known objects are compounded permutations of a set of primary elements. This is modeled as threefold, consisting of fire, water, and earth (ChU 6.2.3); or as five-fold, consisting of space, air, fire, water, and earth (TaiU 2.1.1; see BrSūBh 2.3.1–12 for reconciling these two different models). The elements emerge successively from undifferentiated existence, at first in subtle (i.e., non-perceptible) form. They then undergo a process of division and recombination, so that each element includes portions of the others, to evolve into the coarse (i.e., perceptible) “great elements” (mahābhūtas). Perceptual objects are in fact derivative products that lack existence independent of these primary elements. These elements, however, do not constitute an elemental foundationalism, nor do they bottom out in an atomic foundationalism, because they are ultimately ontologically dependent on something else, namely pure existence (brahman) (BrSūBh 2.2.15–17). Brahman is the nondual ground underlying all objects, the single foundation (adhiṣṭhana) on which the entire universe depends. All objects point back to this independent ground and possess no existence apart from it. Śaṅkara argues that this foundational existence has no dependence on a second thing. It is self-established, irreducible, immutable, and free of space, time, and causation.