Within the depth-psychology corpus, the number nine occupies a contested and largely implicit position, appearing most visibly as a structural designation within the I Ching tradition — where ‘nine’ marks the yang line in hexagram notation — rather than as an independently theorized symbol carrying its own archetypal charge. Unlike the numbers three, four, seven, or ten, which receive sustained symbolic and psychological elaboration by figures such as Jung, von Franz, Plotinus, and Hamaker-Zondag, nine tends to surface as an index or positional marker: ‘nine at the beginning,’ ‘nine in the fifth place,’ and so on, within the commentary systems of Wilhelm, Ritsema-Karcher, and Alfred Huang. The deeper numerological tradition accessible to depth psychology — Pythagorean, Kabbalistic, Neoplatonic — holds nine as the final single digit and thus a number of completion or exhaustion before the return to unity through ten. Plotinus addresses number as a property of authentic Being in the Intellectual realm, and von Franz establishes that natural number carries numinous weight in Jung’s framework. Yet nine as such remains an underdeveloped node in the library: significant by absence, awaiting the synthetic treatment that four, seven, and the quaternio have already received. Its primary interest for scholars lies in tracing what the corpus has not yet said.