In psychology, the term splitting describes a defense mechanism that involves thinking about people in extreme terms (e.g., seeing a person as completely good and later deciding that person is completely evil). Whereas black-and-white thinking is a cognitive bias that pertains to reasoning and affects humans in general, splitting involves human relationships and is associated with specific mental health conditions.
Thinking in extremes makes people susceptible to logical fallacies that involve exaggerated and simplistic representations of an issue, such as the false dilemma fallacy.