The circumplex tradition in interpersonal psychology was inspired by the interpersonal theory of Harry Stack Sullivan (1953) and the sociological theory of George Herbert Mead (1934), and made more explicit and accessible to research by Timothy Leary (1957), who introduced the circular ordering of variables known as the interpersonal circumplex. Interpersonal theory comprises three strands of leading ideas: the principle of complementarity, the principle of rigidity, and the principle of circumplex structure.