Within the depth-psychology and philosophical corpus catalogued in this library, ‘Not Being’ emerges not as simple negation or privation but as a concept with its own positive ontological weight — a domain where the most searching minds have repeatedly found that the apparent void proves philosophically indispensable. The central tension runs from Plato’s Eleatic inheritance, wherein Not-Being is absolutely prohibited as self-contradictory, through his own corrective in the Sophist, where Not-Being is rehabilitated as Otherness — a principle diffused through all things, structurally necessary for predication, falsehood, and difference itself. Parmenides disciplines the paradox further: if the One is not, it nevertheless partakes of greatness, smallness, and equality, forcing Not-Being into a peculiar half-existence. Plotinus responds by relocating Being in eternal actualization, leaving Not-Being as the residue of matter and potentiality. Heidegger transforms the terrain decisively: the ‘not’ embedded in Dasein’s guilt, thrownness, and nullity is not logical negation but an existential structure — Being-the-basis-of-a-nullity. McGilchrist extends this via Heidegger’s ‘das Nichts selbst nichtet’: Nothing actively ‘noths,’ functioning as a generative force rather than an absence. Aurobindo further dissolves the binary, arguing that Nihil, properly examined, is an ‘indefinable Infinite’ that merely appears blank to finite mind. Together these voices establish Not-Being as the indispensable shadow-structure of ontology.