Consistency and standards

The same word, icon or action should mean the same thing everywhere in a product, and the product should follow the conventions people already know from their platform and industry.

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The law

The same word, icon or action should mean the same thing everywhere in a product.

There are two kinds of consistency. Internal consistency is within the product: one name for one thing, one style for one kind of control. External consistency is with the outside world: the conventions of the platform, the web and the industry that people already know.

Where it comes from

This is the fourth of Jakob Nielsen's ten usability heuristics, published in their current form in 1994. Nielsen Norman Group's article on consistency and standards separates internal and external consistency and shows how violations increase the effort people spend learning a product.

The principle predates the list. Platform style guides from the 1980s, written for early graphical operating systems, were built on the idea that applications following shared conventions would be easier to learn as a set.

What it means for an interface

  • One name for one thing. If it is called a "project" on one screen, it is not a "workspace" on the next.
  • One style per kind of control. Primary buttons, links and destructive actions each look the same wherever they appear. A design system is the usual way to enforce this.
  • Follow platform conventions. Gestures, menus and dialog button order should match what the operating system and similar products do.
  • Break a convention only with a reason. A deviation should be worth the learning cost it imposes on every person who meets it.

Examples

Terminology. A product that uses "Delete", "Remove" and "Archive" for the same action in different places makes people wonder whether the actions differ, and some will hesitate to use any of them.

Icons. A magnifying glass that means search everywhere, except on one screen where it means zoom, causes errors on that screen.

Dialog buttons. Placing the confirm button on the side the platform uses for cancel leads to accidental clicks from people who rely on muscle memory.

Where it is misapplied

  • Consistency over fit. Forcing a control into a context where it does not work, only because it is used elsewhere, trades usability for sameness.
  • Copying bad conventions. Following a widespread pattern that is itself confusing spreads the problem.
  • Ignoring external standards. A product can be internally consistent and still clash with everything people know from other products.
  • Freezing the design. Consistency is not a reason never to improve. Change things everywhere at once, not one screen at a time.

Checklist

  • Each concept has one name used across all screens, emails and help content.
  • Each kind of control has one visual style, defined in a shared component.
  • Platform conventions for gestures, menus and dialogs are followed.
  • Icons keep one meaning throughout the product.
  • Every deliberate break from a convention is documented with its reason.

Sources

  1. Nielsen Norman Group. Maintain Consistency and Adhere to Standards (Usability Heuristic #4).
  2. Nielsen, J. (1994). Enhancing the explanatory power of usability heuristics. Proceedings of CHI '94, 152–158. ACM.