Chapter 20: Metaphors, Idioms, and Affordances

Interface designers, especially those of a visual bent, often speak of finding the right metaphor upon which to base their interface designs. They imagine that filling their interface with images of familiar objects from the real world will give their users a pipeline to easy learning. So they create an interface masquerading as an office filled with desks, file cabinets, telephones, and address books, or as a pad of paper or a street of buildings. If you, too, search for that magic metaphor, you will be in august company. Some of the best and brightest designers in the interface world consider metaphor selection as one of their first and most important tasks.

The authors believe that this approach is in error. Strict adherence to metaphors tie interfaces unnecessarily to the workings of the physical world. They have a host of other problems as well: There aren't enough good metaphors to go around; they don't scale well; and the ability of users to recognize them is often questionable, especially across cultural boundaries. Metaphors, especially physical and spatial metaphors, have an extremely limited place in the design of most information-age, software-enabled products. In this chapter, we discuss the reasons for this, as well as the alternatives to design based on metaphors.

Interface Paradigms

There are three dominant paradigms in the conceptual and visual design of user interfaces: implementation-centric, metaphoric, and idiomatic. The implementation-centric interfaces are based on understanding how things work — a difficult proposition. Metaphoric interfaces are based on intuiting how things work — a risky method. Idiomatic interfaces, however, are based on learning how to accomplish things — a natural, human process.

The field of user-interface design progressed from a heavy focus on technology (implementation) to an equally heavy focus on metaphor. There is ample evidence of all three paradigms in contemporary software design, even though the metaphoric paradigm is the only one that has been named and described. Although metaphors are great tools for humans to communicate with each other (this book is filled with them), they are a weak tool for the design of software, and all too often they hamper the creation of truly superior interfaces.

Implementation-centric interfaces

Implementation-centric user interfaces are widespread in the computer industry. These interfaces are expressed in terms of their construction, of how they are built. In order to successfully use them, the user must understand how the software works internally. Following the implementation-centric paradigm means user-interface design based exclusively on the implementation model.

The overwhelming majority of software programs today are implementation-centric in that they show us, without any hint of shame, precisely how they are built. There is one button per function, one dialog per module of code, and the commands and processes precisely echo the internal data structures and algorithms.

We can see how an implementation model interface ticks by learning how to run its program. The problem is that the reverse is also true: We must learn how the program works in order to successfully use the interface.

AXIOM 

Users would rather be successful than knowledgeable.

Engineers want to know how things work, so the implementation-centric paradigm is very satisfying to them (which is the reason, in addition to ease of construction, why so much of our software follows it). Engineers prefer to see the gears and levers and valves because it helps them understand what is going on inside the machine. That those artifacts needlessly complicate the interface seems a small price to pay. Engineers may want to understand the inner workings, but most users don't have either the time or desire. They'd much rather be successful than be knowledgeable, a preference that is often hard for engineers to understand.

Metaphoric interfaces

Metaphoric interfaces rely on intuitive connections that the user makes between the visual cues in an interface and its function. There is no need to understand the mechanics of the software, so it is a step forward from implementation-centric interfaces, but its power and usefulness has been inflated to unrealistic proportions.

When we talk about metaphors in the context of user interface and interaction design, we really mean visual metaphors: a picture used to represent the purpose or attributes of a thing. Users recognize the imagery of the metaphor and, by extension, can understand the purpose of the thing. Metaphors can range from the tiny images on toolbar buttons to the entire screen on some programs — from a tiny scissors on a button indicating Cut to a full-size checkbook in Quicken. We understand metaphors intuitively, but what does that really mean? Webster's Dictionary defines intuition like this:

in-tu-i-tion \in-'tu-wi-shen\ n 1 : quick and ready insight 2 a : immediate apprehension or cognition b : knowledge or conviction gained by intuition c : the power or faculty of attaining to direct knowledge or cognition without evident rational thought and inference

This definition highlights the magical quality of intuition, but it doesn't say how we intuit something. Intuition works by inference, where we see connections between disparate subjects and learn from these similarities, while not being distracted by their differences. We grasp the meaning of the metaphoric controls in an interface because we mentally connect them with other things we have already learned. This is an efficient way to take advantage of the awesome power of the human mind to make inferences. However, this method also depends on the idiosyncratic human minds of users, which may not have the requisite language, knowledge, or inferential power necessary to make those connections.

LIMITATIONS OF METAPHORS

The idea that metaphors are a firm foundation for user-interface design is misleading. It's like worshipping floppy disks because so much good software once came on them. Metaphors have many limitations when applied to modern, information-age systems.

For one thing, metaphors don't scale very well. A metaphor that works well for a simple process in a simple program will often fail to work well as that process grows in size or complexity. File icons were a good idea when computers had floppies or 10MB hard disks with only a couple of hundred files, but in these days of 60 gigabyte hard disks and tens of thousands of files, file icons become too clumsy to use effectively.

Metaphors also rely on associations perceived in similar ways by both the designer and the user. If the user doesn't have the same cultural background as the designer, it is easy for metaphors to fail. Even in the same or similar cultures, there can be significant misunderstandings. Does a picture of an airplane mean "check flight arrival information" or "make airline reservations?"

Finally, although a metaphor offers a small boost in learnability to first-time users, it exacts a tremendous cost after they become intermediates. By reflecting the physical world of mechanisms, most metaphors firmly nail our conceptual feet to the ground, forever limiting the power of our software. We'll discuss this issue with metaphors later in this chapter.

Our definition of intuition indicates that rational thought is not required in the process of intuiting. In the computer industry, and particularly in the user-interface design community, the word intuitive is often used to mean easy-to-use or easy-to-understand. Ease-of-use is obviously important, but it doesn't promote our craft to attribute its success to metaphysics. Nor does it help us to devalue the precise meaning of the word. There are very real reasons why people understand certain interfaces and not others.

INTUITION, INSTINCT, AND LEARNING

There are certain sounds, smells, and images that make us respond without any previous conscious learning. When a small child encounters an angry dog, she instinctively knows that bared fangs signal great danger even without any previous learning. The encoding for such recognition goes deep. Instinct is a hard-wired response that involves no conscious thought. Intuition is one step above instinct because, although it also requires no conscious thought, it is based on a web of knowledge learned consciously.

Examples of instinct in human-computer interaction include the way we are startled and made apprehensive by gross changes in the image on the screen, find our eyes drawn inexorably to the flashing advertisement on a Web page, or the way we react to sudden noises from the computer or the smell of smoke rising from the CPU.

Intuition is a middle ground between having consciously learned something and knowing something instinctively. If we have learned that things glowing red can burn us, we tend to classify all red-glowing things as potentially dangerous until proven otherwise. We don't necessarily know that the particular red-glowing thing is a danger, but it gives us a safe place to begin our exploration.

What we commonly refer to as intuition is actually a mental comparison between a new experience and the things we have already learned. You instantly intuit how to work a wastebasket icon, for example, because you once learned how a real wastebasket works, thereby preparing your mind to make the connection years later. But you didn't intuit how to use the original wastebasket. It was just an extremely easy thing to learn. This brings us to the third type of interface, based on the fact that the human mind is an incredibly powerful learning machine that constantly and effortlessly learns new things.

Idiomatic interfaces

Idiomatic design, what Ted Nelson has called "the design of principles," (1990) is based on the way we learn and use idioms — figures of speech like "beat around the bush" or "cool." Idiomatic user interfaces solve the problems of the previous two interface types by focusing not on technical knowledge or intuition of function, but rather on the learning of simple, non-metaphorical visual and behavioral idioms to accomplish goals and tasks.

Idiomatic expressions don't provoke associative connections the way metaphors do. There is no bush and nobody is beating anything. Idiomatically speaking, something can be both cool and hot and be equally desirable. We understand the idiom simply because we have learned it and because it is distinctive, not because we understand it or because it makes subliminal connections in our minds. Yet, we are all capable of rapidly memorizing and using such idioms: We do so almost without realizing it.

If you cannot intuit an idiom, neither can you reason it out. Our language is filled with idioms that, if you haven't been taught them, make no sense. If we say, "Uncle Joe kicked the bucket," you know what we mean even though there is no bucket or kicking involved. You can't know this by thinking through the various permutations of smacking pails with your feet. You can only learn this from context in something you read or by being consciously taught it. You remember this obscure connection between buckets, kicking, and dying only because humans are good at remembering things like this.

The human mind has a truly amazing capacity to learn and remember large numbers of idioms quickly and easily without relying on comparisons to known situations or an understanding of how or why they work. This is a necessity, because most idioms don't have metaphoric meaning at all, and the stories behind most others were lost ages ago.

GRAPHICAL INTERFACES ARE LARGELY IDIOMATIC

It turns out that most of the elements of intuitive graphical interfaces are actually visual idioms. Windows, title bars, close boxes, screen-splitters, hyperlinks, and drop-downs are things we learn idiomatically rather than intuit metaphorically. The Macintosh's use of the trashcan to eject a floppy or ZIP disk is purely idiomatic (and many designers consider it a poor idiom), despite the visual metaphor of the trash can itself.

The ubiquitous mouse input device is not metaphoric of anything, but rather is learned idiomatically. There is a scene in the movie Star Trek IV where Scotty returns to twentieth-century Earth and tries to speak into a mouse. There is nothing about the physical appearance of the mouse that indicates its purpose or use, nor is it comparable to anything else in our experience, so learning it is not intuitive. However, learning to point at things with a mouse is incredibly easy. Someone probably spent all of three seconds showing it to you the first time, and you mastered it from that instant on. We don't know or care how mice work, and yet even small children can operate them just fine. That is idiomatic learning.

Ironically, many of the familiar GUI elements that are often thought of as metaphoric are actually idiomatic. Artifacts like resizable windows and endlessly nested file folders are not really metaphoric — they have no parallel in the real world. They derive their strength only from their easy idiomatic learnability.

GOOD IDIOMS MUST BE LEARNED ONLY ONCE

We are inclined to think that learning interfaces is hard because of our conditioning based on experience with implementation-centric software. These interfaces are very hard to learn because you need to understand how the software works internally to use them effectively. Most of what we know we learn without understanding: things like faces, social interactions, attitudes, melodies, brand names, the arrangement of rooms, and furniture in our houses and offices. We don't understand why someone's face is composed the way it is, but we know that face. We recognize it because we have looked at it and automatically (and easily) memorized it.

AXIOM 

All idioms must be learned; good idioms need to be learned only once.

The key observation about idioms is that although they must be learned, they are very easy to learn, and good ones only need to be learned once. It is quite easy to learn idioms like "neat" or "politically correct" or "the lights are on but nobody's home" or "in a pickle" or "take the red-eye" or "grunge." The human mind is capable of picking up idioms like these from a single hearing. It is similarly easy to learn idioms like radio buttons, close boxes, drop-down menus, and comboboxes.

BRANDING AND IDIOMS

Marketing and advertising professionals understand well the idea of taking a simple action or symbol and imbuing it with meaning. After all, synthesizing idioms is the essence of product branding, in which a company takes a product or company name and imbues it with a desired meaning. The golden arches of McDonalds, the three diamonds of Mitsubishi, the five interlocking rings of the Olympics, even Microsoft's flying window are non-metaphoric idioms that are instantly recognizable and imbued with common meaning. The example of idiomatic branding shown in Figure 20-1 illustrates its power.

Figure 20-1: Here is an idiomatic symbol that has been imbued with meaning from its use, rather than by any connection to other objects. For anyone who grew up in the 1950s and 1960s, this otherwise meaningless symbol has the power to evoke a shiver of fear because it represents nuclear radiation. Visual idioms, such as the American flag, can be just as powerful as metaphors, if not more so. The power comes from how we use them and associate them, rather than from any innate connection to real-world objects.