Mode error - Definition and Overview

A mode error occurs when a user of something performs an action that is appropriate to a different mode and gets an unexpected and undesired response.

Depending on the design, this undesired response can range all the way from a minor annoyance to a full fledged disaster. The annoyance happens most often in computer software, as described in the Excel example in the External links section below. An example of a case that could be a disaster is if a driver is conditioned by a four way stop sign near his or her home to assume that similar intersections will also be four way stops. If it happens to be only two way, the driver could proceed through if he or she sees no other cars, and especially if there is an obstructed view, a car could come though and hit the first car broadside.

The above example is just one of many that shows why modes should be avoided if at all possible, although there are times when modes are appropriate (See Apple's Human Interface Guidelines (http://developer.apple.com/documentation/mac/HIGuidelines/HIGuidelines-27.html)). If modes must be used, there should at the minimum be clear indicators of the current mode to help prevent mode errors. The UNIX text editor vi can be notoriously difficult for beginners precisely because it uses modes, and the default, in early versions anyway, is for mode indication to be turned off. Programmers and other practitioners of interaction design such as Larry Tesler have been using the phrase "Don't Mode Me In" for years as a rally cry to eliminate or reduce modes. [1] (http://www.byte.com/art/9608/sec4/art3.htm)

See also

• Human computer interaction
• Interaction design
• modeless
• GUI

External links

• Definition of mode error at Usability First (http://www.usabilityfirst.com/glossary/main.cgi?function=display_term&term_id=655)
• An Example of a mode error in Excel (http://www.hcibook.com/e3/casestudy/excel-mode)