Dichotomous thinking also known as all-or-none thinking or black and white thinking is a type of thinking or cognition in which a person classifies something into two absolute categories rather than a range or spectrum between two categories ("shades of gray").
Role in Depression & Mood Disorders
Dichotomous thinking is often present in many mood disorders, including depression and . Cognitive behavioral therapy is an approach to treating depression which focuses on eliminating cognitive distortions; in this framework, dichotomous thinking is seen as one of these distortions.
Feminists have suggested that dichotomous thinking is associated with patriarchal and hierarchical structures in society, and creates unnecessarily oppositional relationships between different areas of knowledge. Holism and continuous thinking are presented as alternatives to this approach. 
- Page 467 A Century of Social Work and Social Welfare at Penn by Ram A. Cnaan, Melissa E. Dichter