Within the depth-psychology corpus, ‘Letter’ operates on at least three distinct registers that rarely converge but collectively reveal its theoretical density. First, and most philosophically charged, is Lacan’s sustained engagement with Poe’s ‘The Purloined Letter’ in his seminar of the same name, where the letter becomes the paradigmatic signifier: an object whose material existence and circuit of displacement constitute the symbolic order itself, indifferent to any particular content. Here the letter is not communication but structure — it situates subjects, confers power, and determines identity through its very itinerary. Second, the corpus treats the letter as a primary historical document: Jung’s two volumes of correspondence, totalling several thousand letters, serve as indispensable clinical and intellectual archives, while Hillman’s archived letters to correspondents such as Ritsema, Giegerich, and Berry chart the evolution of archetypal psychology in real time. Third, the philological tradition represented by Benveniste explores the letter as grapheme — the written unit that crystallises the tension between letter and spirit inherited from Paul, and that embodies the civilisational conflict between oral and literate cultures. Jaynes adds a fourth dimension, reading ancient letters as archaeological evidence for the historical emergence of subjective consciousness. Auerbach attends to the letter as a literary genre, analysing how epistolary rhetoric encodes ideology. These threads converge on a shared concern: the letter as a vehicle through which power, interiority, and symbolic order are simultaneously constituted and concealed.