This thesis is a critical examination of the question of the fourfold, or quaternities, in the thought of C.G. Jung, as well as an in-depth comparison with the four-fold structures of Jacques Lacan and Sergius Bulgakov. I define quaternities as visual or structural formations conceived in four parts, and I center this study on Jung because I see him as the first thinker to seriously examine the place of quaternity in psychology and modern thought. Part of the work of this thesis will be to give a clear view of Jung's quaternal theories, distinguishing the novelty and authenticity of his work from what has been made of it by subsequent New Age and Jungian thinkers. Jacques Lacan, who uses the term "quadrilateral" to describe his formations, will be contrasted with Jung on several counts. First of all, whereas the Jungian quaternity aims to perfectly integrate its various elements, especially when viewed from the perspective of the fourth element of the quaternity, the Lacanian fourth works in the opposite direction, putting into question any reading of the structure which demands resolution and integration. Lacan's quadrilaterals also avoid the complementarity which is always an important aspect of Jungian quaternity, instead opting for a supplementary logic. Sergius Bulgakov avoids, at least in his later work, referring to quaternities, but, in his reading of Sophia (Wisdom), she clearly functions as something of a fourth within the Christian Trinity. Bulgakov's primary contribution is to provide an answer to Jung's complaint that the Christian Trinity has suppressed its fourth and become unbalanced. The fourth that Bulgakov articulates in the form of Sophia is very different from what Jung had argued for. That is, instead of changing the Trinity into a Quaternity Bulgakov maintains that Sophia underlines the "tri-unity" of the Trinity, and functions not a fourth amidst its members, but as a necessary element in order to both bring out the distinctiveness of each person of the Trinity as well as communicate their common identity. / Religion