Don Norman's 6 Fundamental Interaction Principles

In his landmark work The Design of Everyday Things, Don Norman synthesized cognitive psychology into six universal design principles governing how humans interact with artifacts:

1. Affordance: The fundamental property of an object that indicates what operations are physically or logically possible (e.g., a chair affords sitting; a digital input affords typing).
2. Signifier: Visual, auditory, or haptic cues that communicate where and how an action should take place (e.g., a drop-shadow on a button signaling clickability).
3. Constraints: Limits placed on user actions to prevent invalid inputs and guide mental focus.
4. Mapping: The spatial, physical, or conceptual relationship between controls and their effects in the world.
5. Feedback: Immediate, unambiguous confirmation that the system has received and processed an action.
6. Conceptual Model: The user's internal mental model of how the system operates, shaped by interface cues.