Accessibility and usability have a lot in common. In fact, I’d argue that they have so much in common that they’re just a different lens on the same thing.
When we talk about usability, we talk about making our work understandable, clear, consistent, flexible. We could easily talk about making our work perceivable, operable, understandable, and robust. Those sound like excellent ways to make our work usable! They’re also the four WCAG principles.
When we talk about usability, what we usually mean making it usable for a particular slice of our users. The ones that sit in the middle of a bell curve.
For me, accessibility means extending our definition of usable to include a wider audience. How do we make our work usable for more of our users?
We can never make it usable for every single human on the planet. But we can aim for that and make our work more usable, and more accessible, for more of users.