In every respect the burden is hard on those who attack an almost universal opinion. They must be very fortunate as well as unusually capable if they obtain a hearing at all.
?span>John Stuart Mill, from "The Subjection of Women"
Many interface requirements specify that the resulting product be intuitive, or natural. However, there is no human faculty of intuition, as the word is ordinarily meant; that is, knowledge acquired without prior exposure to the concept, without having to go through a learning process, and without having to use rational thought. When an expert uses what we commonly call his intuition to make a judgment, with a speed and accuracy that most people would find beyond them, we find that he has based his judgment on his experience and knowledge. Often, experts have learned to use methods and techniques that nonexperts do not know. Task experts often use cues of which others are not aware or that they do not understand. Expertise, unlike intuition, is real.
When users say that an interface is intuitive, they mean that it operates just like some other software or method with which they are familiar. Sometimes, the word is used to mean habitual, as in "The editing tools become increasingly intuitive over time." Or, it can mean already learned, as was said of a new aircraft navigation device: "Like anything, it can be learned, but it would take a lot of experience to do it intuitively" (Collins 1994).
Another word that I try to avoid in discussing interfaces is natural. Like intuitive, it is usually not defined. An interface feature is natural, in common parlance, if it operates in such a way that a human needs no instruction. This typically means that there is some common human activity that is similar to the way the feature works. However, it is difficult to pin down what is meant by similar. Similarities or analogies can occur in many ways. Certainly, that the cursor moves left when a mouse is pushed to the left and right when the mouse is pushed to the right is natural. Here, the term natural equates to very easily learned. Although it may be impossible to quantify naturalness, it is not too difficult to quantify learning time.
The use of the mouse itself is often claimed to be natural and intuitive. It is difficult to do the experiment now, when the use of this most famous of GIDs is so widespread, but when it was less well known, I asked people unfamiliar with the mouse to use a Macintosh. My protocol was to run a program called The Manhole, an entertaining and well-designed children's exploration game that required no input beyond clicking at various locations on the display. With the keyboard removed from the computer, I would point to the mouse and say, "This is the mouse that you use to operate the game. Go ahead, give it a try." If asked any questions, I'd say something nonspecific, such as "Try it." The reaction of an intelligent Finnish educator who had never seen a Macintosh but was otherwise computer literate was typical: She picked up the mouse.
Nowadays, this might seem absurd, but the same point was made in one of the Star Trek series of science fiction movies. The space ship's engineer has been brought back into our time, where (when) he walks up to a Macintosh. He picks up the mouse, bringing it to his mouth as if it were a microphone, and speaks to it, with a heavy Scots accent: "Computer,..." The audience laughs at his mistake. I admired the creators of the film for recognizing that the use of the mouse was not something you could expect everyone to immediately guess. In the case of my Finnish subject, her next move was to turn the mouse over and to try rolling the ball. Nothing happened. She shook the mouse, and then she held the mouse in one hand and clicked the button with the other. No effect. Eventually, she succeeded in operating the game by holding the mouse in her right hand, rolling the ball on the bottom with her fingers, and clicking the button with her left hand.
These experiments make the point that an interface's ease of use and speed of learning are not connected with the imagined properties of intuitiveness and naturalness. The mouse is very easy to learn: All I had to do, with any of the test subjects, was to put the mouse on the desk, move it, and click on something. In five to ten seconds, they learned how to use the mouse. That's fast and easy, but it is neither intuitive nor natural. No artifact is.
The belief that interfaces can be intuitive and natural is often detrimental to improved interface design. As a consultant, I am frequently asked to design a "better" interface to a product. Usually, an interface can be designed such that, in terms of learning time, eventual speed of operation (productivity), decreased error rates, and ease of implementation, it is superior to both the client's existing products and competing products. Nonetheless, even when my proposals are seen as significant improvements, they are often rejected on the grounds that they are not intuitive. It is a classic Catch-22: The client wants something that is significantly superior to the competition. But if it is to be superior, it must be different. (Typically, the greater the improvement, the greater the difference.) Therefore, it cannot be intuitive, that is, familiar. What the client wants is an interface with at most marginal differences from current practice which almost inevitably is Microsoft Windows that, somehow, makes a major improvement. This can be achieved only on the rare occasions when the original interface has some major flaw that is remedied by a minor fix. (Parts of this section are based on Raskin 1994.)