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What Are the Four Major Categories of Accessibility?

Sep 13, 2019

The Web Content Accessibility Guidelines (WCAG) are organized by four main principles, which state that content must be POUR: Perceivable, Operable, Understandable, and Robust. WCAG is the most-referenced set of standards in website accessibility lawsuits and is widely considered the best way to achieve accessibility.

Content must be POUR


Information and user interface components must be presented to users in ways they can perceive. This means that users must be able to comprehend the information being depicted: It can't be invisible to all their senses.

Perceivable Guidelines

  • Text Alternatives: Provide text alternatives for any non-text content so that it can be changed into other forms people need, such as large print, braille, speech, symbols or simpler language.
  • Time-based Media: Provide alternatives for time-based media.
  • Adaptable: Create content that can be presented in different ways (for example simpler layout) without losing information or structure.
  • Distinguishable: Make it easier for users to see and hear content including separating foreground from background.


User interface components and navigation must be operable: The interface cannot require interaction that a user cannot perform.

Operable Guidelines

  • Keyboard Accessible: Make all functionality available from a keyboard.
  • Enough Time: Provide users enough time to read and use content.
  • Seizures and Physical Reactions: Do not design content in a way that is known to cause seizures or physical reactions.
  • Navigable: Provide ways to help users navigate, find content, and determine where they are.
  • Input Modalities: Make it easier for users to operate functionality through various inputs beyond keyboard.


Information and the operation of a user interface must be understandable: Users must be able to understand the information as well as the operation of the user interface.

Understandable Guidelines

  • Readable: Make text content readable and understandable.
  • Predictable: Make Web pages appear and operate in predictable ways.
  • Input Assistance: Help users avoid and correct mistakes.


Content must be robust enough that it can be interpreted reliably by a wide variety of user agents, including assistive technologies: As technologies and user agents evolve, the content should remain accessible.

Robust Guideline

  • Compatible: Maximize compatibility with current and future user agents, including assistive technologies.

Important note

Much of the content related to WCAG principles and guidelines has been copied verbatim from WCAG 2.1 and supporting W3C documentation. It was organized and provided in this way in an attempt to most effectively answer the question of the four main categories, or principles, of accessibility.

How to test for WCAG compliance

We believe WCAG 2.1 provides the best framework for achieving accessibility. Here's how testing for WCAG compliance breaks down into identifying the accessibility barriers people with different disability types may face on the web.

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