The acorn functions in the depth-psychology corpus primarily as the central metaphor of James Hillman’s ‘acorn theory,’ the organizing image of his 1996 work The Soul’s Code. There, the acorn names the innate image or daimon that each soul carries into life — the compressed, pre-formed essence of individual character and calling, analogous to the oak’s entire destiny contained within the seed. Hillman draws on Platonic, Neoplatonic, and mythological sources to argue that the acorn precedes both nature and nurture as a principle of individuation, belonging mythically to the primordial realm of Artemis and the Arcadian landscape before civilization’s cultivating mother-goddess Demeter. The acorn thus encodes calling, fate, genius, and soul in a single organic image, serving interchangeably with terms such as daimon, angel, character, and paradigm. A recurrent tension in the passages concerns the risk of reading the acorn through a merely naturalistic or developmental lens — a ‘naturalistic fallacy’ Hillman explicitly resists, insisting the soul’s nature may be neither natural nor straightforwardly human. Gabor Maté extends the metaphor into a biopsychosocial register, emphasizing environmental conditions as prerequisites for the acorn’s actualization. Rudhyar’s astrological philosophy offers a parallel seed-monad cosmology. Etymological and linguistic treatments of the Greek balanos (‘acorn’) in Beekes provide a philological counterpoint, situating the term within Indo-European botanical and symbolic vocabularies.