This dissertation is a contribution to the contemporary field of phenomenological psychopathology, or the phenomenological study of psychiatric disorders. The work proceeds with two major aims. The first is to show how a phenomenological approach can clarify and illuminate the nature of psychopathology—specifically those conditions typically labeled as major depressive disorder and bipolar disorder. The second is to show how engaging with psychopathological conditions can challenge and undermine many phenomenological presuppositions, especially phenomenology’s status as a transcendental philosophy and its corresponding (...) anti-naturalistic outlook. In the opening chapter, I articulate the three layers of the subject matter of phenomenological research—what I refer to as “existentials,” “modes,” and “prejudices.” As I argue, while each layer contributes to what we might call the “structure” of human existence, they do not do so in the same way, or to the same degree. Because phenomenological psychopathology—and applied phenomenology in general—aims to characterize how the structure of human existence can change and alter, it is paramount that these layers be adequately delineated and defined before investigating these changes. In chapters two through five, I conduct hermeneutic and phenomenological investigations of psychopathological phenomena typically labeled as major depressive disorder or bipolar disorder. These investigations address the affective aspects of depression and mania, and the embodied aspects of depression. In addition to clearly articulating the nature of these phenomena, I show how certain psychopathological conditions involve changes in the deepest or most fundamental layer of human existence—what I refer to as existentials. As I argue, many of the classical phenomenologists (including Husserl and Heidegger) believed that these structural features were necessary, unchanging, and universal. However, this presupposition is challenged through the examination of psychopathological and neuropathological conditions, undermining the status of phenomenology as a transcendental philosophy. While this challenge to classical phenomenology is only sketched in the early chapters, in chapters six and seven I develop it in more detail in order to achieve two distinct ends. In chapter six I argue that psychopathology and neuropathology not only challenge phenomenology’s status as a transcendental philosophy, but also supply a key to developing a phenomenological naturalism (which I contrast with a naturalized phenomenology). Phenomenological naturalism, as I articulate it, is a position in which phenomenology is not subsumed by the metaphysical and methodological framework of the natural sciences, but nonetheless maintains the capacity to investigate how the natural world stands independent of human subjectivity (and how events in the natural world can bring about changes in the most fundamental structures of human existence). In the seventh chapter I argue that a phenomenology in which existentials are contingent and variable rather than necessary and unchanging allows phenomenologists to contribute to new dimensional approaches to psychiatric classification. Rather than begin from distinct categories of disorder, these approaches begin from distinct core features of human existence. These features, referred to as either dimensions or constructs, can vary in degree and are studied in both normal and pathological forms. (shrink)