The interpersonal circle or interpersonal circumplex is a model for conceptualizing, organizing, and assessing interpersonal behavior, traits, and motives (Wiggins, 2003). The interpersonal circumplex is defined by two orthogonal axes: a vertical axis (of status, dominance, power, or control) and a horizontal axis (of solidarity, friendliness, warmth, or love). In recent years, it has become conventional to identify the vertical and horizontal axes with the broad constructs of agency and communion (Horowitz, 2004). Thus, each point in the interpersonal circumplex space can be specified as a weighted combination of agency and communion.
Placing a person near one of the poles of the axes implies that the person tends to convey clear or strong messages (of warmth, hostility, dominance or submissiveness). Conversely, placing a person at the midpoint of the agentic dimension implies the person conveys neither dominance nor submissiveness (and pulls neither dominance nor submissiveness from others). Likewise, placing a person at the midpoint of the communal dimension implies the person conveys neither warmth nor hostility (and pulls neither warmth nor hostility from others).
The interpersonal circumplex can be divided into broad segments (such as fourths) or narrow segments (such as sixteenths), but currently most interpersonal circumplex inventories partition the circle into eight octants. As one moves around the circle, each octant reflects a progressive blend of the two axial dimensions.
There exist a variety of psychological tests designed to measure these eight interpersonal circumplex octants. For example, the Interpersonal Adjective Scales (IAS; Wiggins, 1995) is a measure of interpersonal traits associated with each octant of the interpersonal circumplex. The Inventory of Interpersonal Problems (IIP; Horowitz, Alden, Wiggins, & Pincus, 2000) is a measure of problems associated with each octant of the interpersonal circumplex, whereas the Inventory of Interpersonal Strengths (IIS; Hatcher & Rogers, 2009) is a measure of strengths associated with each octant. The Circumplex Scales of Interpersonal Values (CSIV; Locke, 2000) is a 64-item measure of the value individuals place on interpersonal experiences associated with each octant of the interpersonal circumplex. The Person's Relating to Others Questionnaire (PROQ), the latest version being the PROQ3 is a 48-item measure developed by the British doctor John Birtchnell. Finally, the Impact Message Inventory-Circumplex (IMI; Kiesler, Schmidt, & Wagner, 1997) assesses the interpersonal dispositions of a target person, not by asking the target person directly, but by assessing the feelings, thoughts, and behaviors that the target evokes in another person. Since interpersonal dispositions are key features of most personality disorders, interpersonal circumplex measures can be useful tools for identifying or differentiating personality disorders (Kiesler, 1996; Leary, 1957; Locke, 2006).
During the twentieth century, there were a number of efforts by personality psychologists to create comprehensive taxonomies to describe the most important and fundamental traits of human nature. Leary would later become famous for his controversial LSD experiments at Harvard. His circumplex, developed in 1950, is a circular continuum of personality formed from the intersection of two base axes: Power and Love. The opposing sides of the power axis are dominance and submission, while the opposing sides of the love axis are love and hate (Wiggins, 1996).
Leary argued that all other dimensions of personality can be viewed as a blending of these two axes. For example, a person who is stubborn and inflexible in their personal relationships might graph her personality somewhere on the arc between dominance and love. However, a person who exhibits passive–aggressive tendencies might find herself best described on the arc between submission and hate. The main idea of the Leary Circumplex is that each and every human trait can be mapped as a vector coordinate within this circle.
Furthermore, the Leary Circumplex also represents a kind of bull's eye of healthy psychological adjustment. Theoretically speaking, the most well-adjusted person of the planet could have their personality mapped at the exact center of the circumplex, right at the intersection of the two axes, while individuals exhibiting extremes in personality would be located on the circumference of the circle.
The Leary Circumplex offers three major benefits as a taxonomy. It offers a map of interpersonal traits within a geometric circle. It allows for comparison of different traits within the system. It provides a scale of healthy and unhealthy expressions of each trait. 
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