Courtesy of Apple

Don Norman and Bruce Tognazzini wrote the book—literally—on graphical user interfaces.

November 16, 2015

Don Norman’s best-selling book The Design of Everyday Things popularized the user-centric design ideas now embodied by the Macintosh. Bruce “Tog” Tognazzini was Apple employee No. 66 and wrote the first eight editions of Apple Human Interface Design Principles, the company’s design Bible.

Now, in a harshly worded Fast Company essay, they both blasted Apple APPL for having abandoned those principles.

“Once upon a time,” they begin, “Apple was known for designing easy-to-use, easy-to-understand products. It was a champion of the graphical user interface, where it is always possible to discover what actions are possible, clearly see how to select that action, receive unambiguous feedback as to the results of that action, and have the power to reverse that action—to undo it—if the result is not what was intended.”

“No more. Now, although the products are indeed even more beautiful than before, that beauty has come at a great price. Gone are the fundamental principles of good design: discoverability, feedback, recovery, and so on. Instead, Apple has, in striving for beauty, created fonts that are so small or thin, coupled with low contrast, that they are difficult or impossible for many people with normal vision to read. We have obscure gestures that are beyond even the developer’s ability to remember. We have great features that most people don’t realize exist.”

Typefaces too small to read can be enlarged, but Norman and Tognazzini’s complaints about Apple’s new interface paradigms are not so easily addressed. The problem with controls based on gestures (swipes with one or many fingers) and touches (using different degrees of force) is that there is no way to see what operations are possible just by looking at the screen.

Apple, they write, is destroying design. If the company were taking an elementary class in interaction design, it would fail.

At 5,300 words, Norman and Tognazzini’s jeremiad is too long, too meandering and too harsh. But the problems they point out are real. It will be interesting to see how Apple responds.

See also: What the Apple Watch might be, a Fortune post that includes speculation by Tognazzini about the company’s first smartwatch which turned out to be amazingly prescient.

Follow Philip Elmer-DeWitt on Twitter at @philiped. Read his Apple AAPL coverage at fortune.com/ped or subscribe via his RSS feed. You might also want to subscribe to Data Sheet, Fortune’s daily newsletter on the business of technology.

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