Constraints
Physical, semantic, cultural and logical constraints guide our actions and aid in interpretation.
Constraints give us clues
They allow us to determine a course of action by limiting the possible actions available to us.
Physical constraints
Restrict the possible operations; for example, a mouse cursor cannot be moved outside the screen. This boundary prevents a user from losing their visual anchor.
Semantic constraints
Provide clues to where actions can be performed; for instance, a socket is restricted in where the plug pins can be inserted. The constraint of only being inserted one way eliminates user error.
Cultural constraints
Social conventions, such as waiting in a queue to be served, create a signifier of where to stand.
Logical constraints
Help determine the alternatives; for example, scroll bars indicate that content exceeds the viewport, and that we should scroll.
Origin
Constraints are one part of the fundamental principles of interaction, defined by American researcher, professor and author Don Norman, which can be applied to make products and services efficient, effective and delightful to use.