Introduction

It is not difficult to find cases in everyday life where inconsistencies facilitate our activities. For example, think of the rather large class of events that might be considered exceptions from otherwise routine tasks. To remove a recalcitrant stain from an article of my clothing, I might have to soak the garment before putting it in the wash. Soaking is an exception from the normal routine of washing clothes, and as such, represents a kind of inconsistency in that routine -- namely, I carry out the "wash clothes" procedure differently if it is being applied to a set of garments containing a stained garment than a set of garments without such an object. If my highest priority were to have a single, consistent procedure for washing my clothes, I would either have to soak everything before washing, or give up the notion of removing recalcitrant stains. Cases of advantageous user interface inconsistencies can also be found; largely on the strength of these a "case against user interface consistency" has recently been mounted [Grudin, 1989].

Yet the trend and effort toward creating interface consistency across a wide range of applications and system environments is, if anything, increasing. This quest for common "look and feel" across product families is often taking the form of describing a "common user interface" (CUI) that specifies salient details of user interfaces. Indeed,...