Same look? Same behavior. Always.
Similar interface elements must behave in similar ways. Across all contexts. Creating predictable interaction patterns. Through consistent affordances. Signifiers. Feedback mechanisms.
Enabling users to apply learned behaviors reliably. Rather than discovering context-specific variations. For identical-appearing elements.
Norman's foundational work (1988) on affordances and signifiers established the pattern. Users form behavioral expectations. From visual cues.
When button-shaped elements consistently respond to clicks? With identical feedback patterns? Users develop reliable mental models. Predicting system behavior.
Nielsen's consistency heuristic (1994) demonstrated the impact. Through hundreds of usability evaluations. Behavioral inconsistency? Ranks among the most severe usability violations.
When similar elements behave differently? Users experience confusion. Errors. Reduced confidence. In system predictability.
Fundamentally undermining interface usability.
Norman's The Design of Everyday Things (1988) established foundational concepts explaining behavioral consistency's cognitive importance. His distinction between affordances (action possibilities objects provide) and signifiers (perceivable indicators of where actions occur) revealed that consistent behavioral mapping between signifiers and affordances enables predictable interaction. When button-shaped elements consistently afford clicking and provide identical feedback (visual state changes, auditory cues, system responses), users develop accurate conceptual models—internal representations of how systems work enabling behavior prediction. Inconsistent behavioral mapping (button-shaped elements sometimes clickable, sometimes not; identical appearances producing different outcomes) prevents reliable mental model formation forcing users to treat each interaction as novel requiring conscious evaluation.
Norman's research on gulfs—the gulf of execution (difficulty determining how to perform actions) and gulf of evaluation (difficulty determining action effects)—demonstrated that behavioral consistency bridges these gulfs. Consistent signifiers (visual cues indicating interactivity) reduce the gulf of execution by making action possibilities obvious. Consistent feedback (predictable system responses) reduces the gulf of evaluation by clearly communicating action outcomes. Behavioral inconsistency widens both gulfs—users cannot confidently determine which elements afford actions or predict action consequences creating continuous uncertainty and elevated cognitive load.
Nielsen's usability heuristics (1994) positioned consistency as fundamental principle through extensive evaluation demonstrating behavioral inconsistency constitutes severe usability problems. His research through thousands of usability evaluations revealed users form behavioral expectations rapidly—within first exposures to interface patterns. Once established, these expectations strongly influence subsequent interactions—users approach similar-appearing elements expecting identical behaviors. Violating expectations (similar elements behaving differently) creates immediate usability failures requiring users to consciously evaluate each interaction possibility rather than leveraging learned patterns creating systematic efficiency penalties.
Card, Moran, and Newell's The Psychology of Human-Computer Interaction (1983) provided quantitative framework for understanding behavioral consistency through their GOMS model (Goals, Operators, Methods, Selection rules). Their research demonstrated that behavioral consistency enables method transfer—users learning one method (interaction sequence achieving goals) can apply it across contexts when behaviors remain consistent. Inconsistent behaviors require learning multiple methods for similar tasks—selecting which method applies in each context creates decision overhead and error potential. Their quantitative analysis showed consistent interaction patterns enable 30-40% faster expert performance through method consolidation and reduced selection rule complexity.
Fitts's Law (1954) research on human motor behavior demonstrated importance of predictable target acquisition—movement time relates predictably to target distance and size. This foundational principle extends to behavioral consistency—when interactive elements maintain consistent target sizes, locations, and response patterns, users develop accurate motor programs enabling efficient interaction. Behavioral inconsistency (varying target sizes, unpredictable locations, inconsistent responses) prevents motor program development forcing continuous visual-motor adjustment increasing interaction time and error rates.