Summary: Overloading different outcomes on similar commands can be confusing. Using the same command for multiple actions enhances usability if the results are conceptually the same.

One way to manage interaction design complexity is to have commands serve double duty. There are two ways of doing this, with different usability implications:

• Generic commands use the same command in different contexts to achieve conceptually the same outcome, even though details of the specific effects might differ.
• Overloaded commands use variants of the same command to achieve different outcomes — sometimes depending on the context and other times depending on where the command appears on the screen.

I discussed generic commands in depth in an earlier article. The most famous generic command these days is the pinch-zoom gesture, which works in most touchscreen user interfaces. In fact, the command is so pervasive that users expect it to work universally — and are sorely disappointed when they encounter an application that doesn’t support it.