A series of principles that user interface designers must understand. The following principles were developed by psychologists to document how people perceive objects. Proximity Related objects must be close together. For example, a description about what is to be entered should be very close to the input field. Similarity Similar objects must resemble each other in some manner. This is the purpose of using icons for the various file types. Although the file names are different, the icons allow them to be recognized as a group. Closure Objects on screen can be incomplete to accommodate a certain design principle. The human mind fills in the gaps when confronted with a partial image. Continuity Care should be taken when objects on screen intersect, because users treat them as one object. Common Fate Elements can be designed to move together. For example, editing buttons on an image window make users aware of their options.