 Throughout his commentaries Śaṅkara employs two related criteria, dependence and persistence, to determine what is real. He defines the real as that which does not change its nature, whereas what is unreal does change (see, e.g., GKBh 2.6; TaiUBh 2.1.1). The primary distinction here is change. Something which persists is more real than what is transient because what is transient is subject to negation. His canonical illustration is a clay pot. One may shape a substantial cause such as clay into new names and forms, from a lump to a pot to a plate. With each new form, the former is destroyed, yet the clay continues through each. This example illustrates his foundational discriminative reasoning of continuity and discontinuity, which determines the relationship of what persists and what does not persist between two things (see  §4.3  below). Accordingly, the clay persisting through causation is relatively more real than the non-persisting lump, pot, and plate forms, because clay is not negatable. In this illustration, clay is analogous to brahman, the underlying existence of the universe, and the pot is analogous to objects.