Universal Principles of Design, Updated and Expanded Third Edition

036 Constraint

Limiting the actions that can be performed to simplify use and prevent error.

Constraints limit the possible actions that can be performed on a system. For example, dimming or hiding options that are not available at a particular time effectively constrains the options that can be selected. Proper application of constraints in this fashion makes designs easier to use and dramatically reduces the probability of error during interaction.1

There are two basic kinds of constraints:

1. Physical constraints — Limiting the range of possible actions by redirecting physical motion in specific ways. The three kinds of physical constraints are paths, axes, and barriers. Paths convert applied forces into linear or curvilinear motion using ...