Choosing a Method
Both graceful degradation and progressive enhancement obviously assist in making a website accessible, yet providing additional usability for those who can take advantage of it. So which one should we choose?
Progressive enhancement is usually preferable to graceful degradation, for the same reason that structural design usually leads to better accessibility than visual design: it starts with the simple basics and adds embellishments on top of that. When designing something from scratch, we should definitely think in terms of progressive enhancement.
If we are maintaining an existing site, trying to improve accessibility and standards conformance, the situation is different. Unless we want to rewrite everything, our only choice is to provide graceful degradation as best we can.
Of course it is also possible to mix both methods on one site, or even on the same page. Progressive enhancement is what we should strive for, though, if we have a choice.
Testing the accessibility is much easier with progressive enhancement than with graceful degradation.
If we work from the point of view of progressive enhancement, we can simply create the basic version and verify that it works. Then we add the enhancements and verify that they work. Okay, this is somewhat simplified: when testing the enhancements we may need to verify that they don’t break the basic version.
I hope this article will prove them wrong once and for all. Anything that improves usability or aesthetics is a good thing. What I (and many others) wish to point out is the danger of relying on non-standard, proprietary or platform-dependent technology. All that should be required for accessing information on the Web is a user agent that supports HTTP and HTML. Such a user agent should be able to access the vital information on any professional site.
Graceful degradation, to some extent, but especially progressive enhancement make this dichotomy possible. It is possible to eat your cake and have it, too. It requires a bit more work, sometimes, but it is often worth it.