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.
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.
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."
...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.
...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: