Communications of the ACM. 37:9, September 1994, pg. 17.

By Raskin, J.

One of the most common terms of praise for an interface is to say that it is “intuitive” (the word should have been “intuitable” but we will bow to convention). Yet the Human Computer Interaction (HCI) literature rarely mentions the word, and for good reason. This note attempts to clarify the meaning of “intuitive” for non-HCI specialists.

The impression that the phrase “this interface feature is intuitive” leaves is that the interface works the way the user does, that normal human “intuition” suffices to use it, that neither training nor rational thought is necessary, and that it will feel “natural.” We are said to “intuit” a concept when we seem to suddenly understand it without any apparent effort or previous exposure to the idea. In common parlance, intuition has the additional flavor of a nearly supernatural ability humans possess in varying degrees. Given these connotations, it is as uncomfortable a term in formal HCI studies as it is a common one in non-technical publications and in informal conversation about interfaces.

As I learned from a talk given by Martin Marshall in Palo Alto (at the May ‘94 BayCHI meeting), a number of commercial magazine-related “usability” labs that rate software qualities give 50% of their weighting to User Satisfaction, 30% to Productivity, and 20% to Intuitiveness. “Intuitiveness” in this context is considered to be a function of percentage of tasks completed and the number of help references made while in the very early stages of using a product.

There are occasional hints of the meaning of “intuitive” in the literature. Stephen Oppenheimer, of the Review Board of InfoWorld magazine, noted in his review of Mathcad 4.0 that “The editing tools become increasingly intuitive over time.” Similarly, Richard Collins in Flying (October 1994 pg. 67), speaking of a new aircraft navigation device, “Like anything, it can be learned, but it would take a lot of experience to do it intuitively.” These uses of the term are uncharacteristic in that immediacy is normally an important aspect of “intuition”. In the usual sense of the word, something cannot become intuitive over time, it is either intuitive or it is not. What Oppenheimer is discussing is not intuition, but learning. When the tools had been learned, he is saying, they became intuitive. This is a strong clue as to the meaning of “intuitive.”

Many claims of intuitiveness, when examined, fail. It has been claimed that the use of a computer’s mouse is intuitive. Yet it is far from that. 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 says: “Computer, …” The audience laughs at his mistake.

But that is just the whimsy of a screenwriter. Or is it? I performed a deliberate experiment some years ago using one of the early Apple Macintosh computers. I loaded a children’s program, The Manhole, where user interaction is strictly (and cleverly) limited to “clicking” on various places on an image. Clicking consists of moving the cursor to some location on the screen by moving the mouse on a surface and momentarily pressing the only button on the mouse. Clicking on certain places yields a new screen. This cold description does not express the delight most people find in running The Manhole program, but that is not relevant here.

My subject was an intelligent, computer-literate, university-trained teacher visiting from Finland who had not seen a mouse or any advertising or literature about it. With the program running, I pointed to the mouse, said it was “a mouse”, and that one used it to operate the program. Her first act was to lift the mouse and move it about in the air. She discovered the ball on the bottom, held the mouse upside down, and proceeded to turn the ball. However, in this position the ball is not riding on the position pick-offs and it does nothing. After shaking it, and making a number of other attempts at finding a way to use it, she gave up and asked me how it worked. She had never seen anything where you moved the whole object rather than some part of it (like the joysticks she had previously used with computers): it was not intuitive. She also did not intuit that the large raised area on top was a button.

But once I pointed out that the cursor moved when the mouse was moved on the desk’s surface and that the raised area on top was a pressable button, she could immediately use the mouse without another word. The directional mapping of the mouse was “intuitive” because in this regard it operated just like joysticks (to say nothing of pencils) with which she was familiar.

From this and other observations, and a reluctance to accept paranormal claims without repeatable demonstrations thereof, it is clear that a user interface feature is “intuitive” insofar as it resembles or is identical to something the user has already learned. In short, “intuitive” in this context is an almost exact synonym of “familiar.”

Given this insight, the measure of intuitiveness used by the magazine usability labs is logical. The percentage of tasks completed increases with increasing intuitiveness since it simply means that the user is already at least partially trained with respect to the feature or set of features under test. Training tends to decrease the time required for task completion, especially at first. Similarly, the number of times the user has to reference help screens increases with decreasing intuitiveness, that is, decreasing familiarity. If the word “intuitive” is replaced by the more readily understood word “familiar” the criterion the magazines have established with respect to intuitiveness seems obvious.

The term “intuitive” is associated with approval when applied to an interface, but this association and the magazines’ rating systems raise the issue of the tension between improvement and familiarity. As an interface designer I am often asked to design a “better” interface to some product. Usually one 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 competing or the client’s own products. Even where my proposals are seen as significant improvements, they are often rejected nonetheless 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 superior, it cannot be the same, so it must be different (typically the greater the improvement, the greater the difference). Therefore it cannot be intuitive, that is, familiar. What the client usually wants is an interface with at most marginal differences that, somehow, makes a major improvement. This can be achieved only on the rare occasions where the original interface has some major flaw that is remedied by a minor fix.

The present rating systems of the magazines and the similar thinking of many users, managers, and marketers about products with significant human interface components serves to preserve the status quo, even when it can be shown that a feature that is completely familiar (intuitive) is deficient. This tendency makes it more difficult for major advances in human interfaces to achieve commercial realization. When I am able to present the argument given here that intuitive = familiar, I find that decision-makers are often more open to new interface ideas.

I suggest that we replace the word “intuitive” with the word “familiar” (or sometimes “old hat”) in informal HCI discourse. HCI professionals might prefer another phrase:

Intuitive = uses readily transferred, existing skills.

It would read very differently–and more honestly–if the magazines discussed above made it clear that ratings were based, for example, 50% on user satisfaction, 30% on productivity, and 20% on familiarity. Note that user satisfaction and early productivity (long-term productivity, though of great importance to users, is not tested) are strongly dependent on familiarity, so that the rating system is further flawed in not being built on a set of independent (orthogonal) bases: the three parameters tend to rise and fall together.

That quality of a new interface paradigm that is commonly titled “intuitive” may well turn out to be one of the worst qualities it can have.

Acknowledgements: I would like to thank Bill Buxton, Donald Norman, Linda Blum, and Bruce Tognazzini for useful suggestions.