Usability Heuristics · heuristic
Consistency & Standards
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Nielsen's H4: users should never have to wonder whether different words, situations or actions mean the same thing. Follow platform and industry conventions (external consistency) and your own established patterns (internal consistency) — every deviation makes users re-learn something they already paid to know.
Where it comes from
In 1868 the first traffic signal outside Westminster used railway semaphore conventions; by the 1920s red-amber-green was a worldwide standard, and today a Mumbai driver can read a Berlin junction without a word of German. Standards compress learning: learn once, apply everywhere. Nielsen's H4 imports that contract into software — and every green 'Cancel' button breaks a promise the whole world made.
Origin: The red-amber-green traffic light (1868→1920s)
In the wild
- ⌘K command palettes
One shortcut now opens search in hundreds of tools — each new app inherits the learning of all the others.
- The cart icon, top right
E-commerce converged on one placement so thoroughly that moving it measurably drops sales.
- Design systems
Tokenised buttons and spacing exist so 'delete' can't accidentally mean three different things across one product.
Further reading
Don't just read it — feel it.
Play the 3-minute game and let your own reactions prove the law.
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