Metaphysics, as the study of the fundamental nature of reality, has long grappled with the question of what constitutes the essence of existence. Two contrasting frameworks have emerged across philosophical traditions: the metaphysics of fullness, which posits a unified, eternal, and unchanging reality, and the metaphysics of emptiness, which emphasizes flux, interdependence, and the absence of inherent essence. The Upanishads and Parmenides exemplify the metaphysics of fullness, asserting a singular, all-encompassing reality, while Buddhism and Heraclitus champion the metaphysics of emptiness, focusing on impermanence and the lack of a fixed substance.
This contrast can be seen as a function in its own right, adding a new function to the established four: thinking, feeling, sensation, and intuition. In Psychological Types, Jung also grappled with this question, as seen from his many quotations from the Tao Te Ching, Buddhism, Heraclitus, and the Vedas. He was a pioneer of the study of metaphysics but ultimately failed to turn his intuition into a coherent, systematic idea.