Psychiatric phenomenology is the study of the assessment of an individual's experience in the world as it relates mainly to the perception of time and also to the perception of spatiality, causality, and materiality. The perception of time plays a key role in how an individual perceives the world and whether or not he or she is experiencing a mental disorder. This is investigated by Henri Ellenberger in his chapter titled, "A Clinical Introduction to Psychiatric Phenomenology and Existential Analysis" and expanded upon by several other phenomenologists, philosophers, and psychologists. The most relevant development of psychiatric phenomenology is categorical analysis, a therapeutic technique of assessing the four coordinates of experience: temporality, spatiality, causality, and materiality. The modem therapeutic implication of the ideas of psychiatric phenomenology, especially its emphasis on the technique of categorical analysis, is practice and research of existential psychology and humanistic therapy techniques. Much can be learned from assessing an individual's mental disorder through his or her experience with temporality and other elements of the world. Specifically, a more developed clinical picture of what the experience with a mental disorder feels like for the individual can be gained through this form of analysis.