Synthesis occupies a pivotal position across several strands of the depth-psychology corpus, functioning simultaneously as a clinical procedure, a philosophical category, and a cosmological principle. In the trauma literature, most fully developed by Onno van der Hart and colleagues working within the structural dissociation framework, synthesis names the foundational mental action by which disparate sensory, affective, and behavioral data are bound together and differentiated to constitute a unified experiential world. It is explicitly placed on a continuum rather than treated as an all-or-nothing achievement, and its failure at the level of mental efficiency is held to underlie dissociative symptomatology. Van der Hart further distinguishes ordinary synthesis from ‘extended synthesis,’ the binding of experience across time that enables learning and personality development. At the clinical level, ‘guided synthesis’ names a systematic therapeutic technique for graduated exposure of personality parts to traumatic memories. In a quite different register, Sri Aurobindo employs synthesis as a spiritual-teleological concept organizing the integration of yoga paths. Hobson’s activation-synthesis hypothesis of dreaming introduces the term into neuropsychological discourse, where synthesis designates the brain’s construction of meaningful experience from random REM-generated signals. Aurobindo’s individualizing synthesis in The Life Divine introduces a metaphysical valence in which the personal self is understood as a selective, evolving construction from transpersonal being. These convergent but non-identical usages—clinical, neurological, and metaphysical—reveal synthesis as a trans-domain hinge concept in depth psychology.