The HBDI is based on the Whole Brain Model, a metaphor for how people tend to use their brains and how their thinking works. In the Whole Brain Model, thinking falls into four preference clusters of equal importance that everyone has access to: The Upper Left Blue A Quadrant specialises in logical, analytical, quantitative, fact-based thinking. The Lower Left Green B Quadrant focuses on details and specialises in planning, organising, and sequencing information. The Lower Right Red C Quadrant places a priority on feelings and the interpersonal, emotional and kinaesthetic aspects of a situation. The Upper Right Yellow D Quadrant synthesises and integrates information and is more intuitive and holistic in its thinking.