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The Four Principles of Accessibility ?>

The Four Principles of Accessibility

The four principles of accessibility are the key factors to consider when building accessible web pages. They are the requirements that must be met for users to be able to make sense of a web page. If you don’t consider these factors, your site may fail to meet the needs of your users, and you could lose business. The four principles are perceivable, operable, understandable and robust.

four puzzle pieces
Four puzzle pieces representing the four principles of web accessibility


Perceivable means that content must be presented in a way that it can be perceived or consumed by the senses. Usually, we assume that to be perceivable online content needs to be visible, but this isn’t always the case. Blind users may require an audio representation of the text and images on a page. A user may even need to use a refreshable braille display as an alternative to sight and sound. There are many different ways to experience text, so providing text is the best way to ensure your website is perceivable. Keep in mind that an image only web page will be very difficult or even impossible for non-sighted users.


To be operable, users must be able to use your website. Usually, when we use the internet we do so with a mouse, so we assume that everyone uses a mouse, but this is not true. When people can not see they are unable to use a mouse so that they will use a keyboard or other assistive technologies. The best way to assure that a site is operable is to make good use of links, form elements, buttons and headings. Also be careful with tabindex as they can easily be misused resulting in an inaccessible website.


Users need to be able to understand the content on your website. There are two ways in which content must be understandable, and the first is the words themselves. The content needs to be clear, precise and easy to read. Using a lot of technical terms on an introduction will make it difficult for users to grasp. That said, understandability is subjective, but you can achieve it by writing for your audience at a level that is suitable for them.

The second part of understandable is related to user interfaces. Users will expect a page to be linear and functional like the other web pages on the internet. If your website isn’t linear or has unexpected functionality, users will not intuitively understand how to use it. The best way to assure your site is understandable is to follow best practices and keep your code standards compliant.


To be robust, a site needs to be available to different types of web browsers and assistive technologies. This also means that the site should continue to be usable as technology advances. The best way to assure that a website is robust is to keep it compliant with standards and code it cleanly and correctly. Technologies may change, but sticking with the standards will keep your site up-to-date.

Also, avoiding obscure technologies like a flash will help. Flash was very popular in the past, but its appeal has faded as its support has waned. Flash is also notoriously difficult to make accessible. Keep this in mind when considering a plugin based technology that may not have staying power.

The four principles of accessibility are important concepts to remember when developing a new website. Not only will these concepts be important considerations for disabled users, but they are also priorities for what is useful to all your customers.

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