One of the worst user interface design errors is the conflation of two unrelated concerns. Unfortunately it is depressingly common.

Take for example Back and Up. Frequently these are conflated into a single button leading to unexpected user behaviour. This is currently bugging me on my Android phone… I use an app that opens a screen that then sends me to my e-mail, I press ‘Back’ expecting to go back to the app but instead the ‘back button’ is overloaded to mean ‘up to parent’ by the mail app so I actually end up in the inbox. It may seem a small thing but believe me it is absolutely infuriating.

Unfortunately for designers precisely the converse is also true… one of the best UI design ideas is to conflate related ideas. Yes, mutual contradiction at work.?

Consider e-mail and facebook messaging, both are basically the same and wrapping them all up in the same ui would make most users pretty happy.

The challenge for the designer then is to locate ideas that seem related not only to the designers of the world but to everyone who will pick up their creation. When they succeed the user sees the world as simpler, more obvious, and less stressful. When they fail the UI seems to be a nightmare to use, a frustration, and often reason enough to seek alternatives.

Moral: Conflate with care!