Universal Principles of Design

• “Nature operates in the shortest way possible.”—Aristotle
• “We are to admit no more causes of natural things than such as are both true and sufficient to explain their appearances.”—Isaac Newton
• “Everything should be made as simple as possible, but not simpler.” —Albert Einstein

Fitts’ Law

The time required to move to a target is a function of the target size and distance to the target.

When affordances are successfully em

employed in a design, it will seem inconceivable that the design could function or be used otherwise.

design objects and environments to afford their intended function,

and negatively afford improper use. For example, stackable chairs should only stack one way.

Mimic familiar objects and environments in abstract contexts (e.g., software interfaces) to imply the way in which new systems can be used

Aesthetic elements like color covers and customizable rings are more than ornaments; the aesthetic elements create a positive relationship with users that, in turn, make such troubles more tolerable and the devices more successful.

idea—images of common items like trash cans and folders leverage our knowledge of how those items function in the real world and, thus, suggest their function in the software environment.13

Images of common physical objects and environments can enhance the usability of a design. For example, a drawing of a three-dimensional button on a computer screen leverages our knowledge of the physical characteristics of buttons and, therefore, appears to afford pressing. The popular “desktop” metaphor used by computer operating systems is based on this