3-3 Noun-Verb versus Verb-Noun Constructions A large class of commands involve applying an action to an object. In operating a word processor, for example, you might take a paragraph and change its typeface; in this case, the object is the paragraph, and the action is the selection of a new font. The interface can allow you to sequence the operations in two ways. You choose either (1) the verb (change font) first and then select the noun (the paragraph) to which the verb should apply or (2) the noun first and then apply the verb. At first glance, it would seem that the situation is symmetrical and the order is of no importance, but in most interface designs, the situation is not symmetrical, and the order (either noun-verb or verb-noun)[6] makes a significant difference in usability. [6] The terminology object-action versus action-object is also used.
Most interface guidelines correctly recommend noun-verb interaction (Apple 1987, Hewlett Packard 1987, IBM 1988, Microsoft 1995). A locus-of-attention analysis shows the benefits. Error reduction. Verb-noun style sets up a mode. Once you have chosen a command in this style, it will take effect on the next selection you make. If there is a delay or a distraction between issuing the command and making the selection, the ensuing action may be surprising when you next make a selection. With noun-verb construction, commands are executed when issued, when your locus of attention is the command. Speed. You do not have to shift your attention away from your content which is what triggered the need to perform an operation to the command and then back to find your place in the content again to make the selection. With noun-verb construction, you make the selection your locus of attention and then switch your attention to the command. There is one change of locus of attention instead of two. Simplicity and reversibility. In the verb-noun paradigm, you need to have an escape or a cancel feature associated with the command; if you issue a command and then decide against it, you are in a mode where the system expects you to make a selection, so a mechanism must be provided so that you can signal the system that you do not want to make a selection, you want to issue another command. In noun-verb construction, if you decide to change your selection, you simply make another selection. No Cancel button or cancel method is necessary.
Every interface guideline I have seen that advocates noun-verb construction also permits the verb-noun style of commands. The Microsoft manual states that verb-noun style is necessary for palettes, such as those for the various brush styles in paint programs (Microsoft 1995). This is not strictly true. A pure noun-verb model is possible: You draw in a default set of attributes, such as a thin black line, and then apply color, width, texture, or whatever via commands. However, we really want to see the full effect of each stroke as we make it with all of its attributes in full flower. The conventional method, whereby you first select the attributes from one or more palettes much as you dip a real brush into this or that paint and then make your mark does lead to the mode errors we have come to expect in such situations. It also makes sense to let the mode you have chosen persist until you deliberately change it. Therefore, it will happen that you start to draw and find unexpected attributes appearing. Fortunately, the appearance of what you are drawing is your locus of attention; if the software is humane, you will be able to immediately undo the offending mark, change the attributes to those desired, and continue working. The mode errors are annoying, and it would be gratifying to find a noun-verb or other nonmodal method that would be effective in this situation, but to the best of my knowledge, nobody has as yet found a solution to this particular problem. In general, the noun-verb paradigm is preferred. Verb-noun methods should be limited to palette selections intended for immediate use. Case Study of a Noun-Verb Fix to a Verb-Noun Problem Workers in various departments of a multinational corporation used a computer system to requisition products. This example illustrates one way to change a seemingly natural verb-noun situation to a noun-verb one. In practice, this change eliminated the errors that the initial design had caused and also speeded the requisitioning process. The original process had three steps. Choose the department from which the order was originating. This consisted of clicking on a check box alongside a department name. One of the check boxes was prechecked as a default. The default was the department in which the computer was situated. Choose the desired items from a scrollable list of items, each item having an associated text box into which you could type the desired quantity for each item. Click on one of two buttons at the bottom of the display: either Cancel Order or Confirm Order.
The first problem was that users failed to select their department when they were ordering from other than their usual computer station. A solution that had been suggested by the company's designers was to provide no default, forcing the user to select a department first, every time. Then, they pointed out, the only possible error would be to choose the wrong department. This solution, however, is annoying to users, who usually work at a specific station and thus might be irritated at having to supply information already available to the system. The problem was a disguised verb-noun situation: You first entered what you wanted to do (deliver these items to the department) and then chose what you wanted to have delivered. When you entered the requisitioning screen, the item or items you needed were, or recently had been, at your locus of attention. Part of the solution was to put the checklist of items at the top of the requisition display. Thus, the user would start by selecting the desired items. The location list, previously unlabeled, was given a descriptive label: "To which department do you want the requisitioned items delivered?" If the system could determine from the user's log-on information the user's department, a new item was automatically added to the top of the list of departments. It was labeled "My Department" and, like the other items on the list, had a check box. The rest of the list contained all of the departments in alphabetical order and a check box for each. When the user placed a check in one of the boxes, a message appeared: "Your items have been requisitioned." The message automatically disappeared at the user's next action. With the redesigned interface, choosing a department represented an action a verb namely, to cause the previously selected items to be sent. Psychologically, it was now an act of closure rather than a preliminary step. Also, note that at this point, the requisition form had been filled in; the user's attention was no longer on the desired items but rather on having them delivered. The work flow now accorded with the path that the user's locus of attention would ordinarily follow. No default location was needed, because the interface supplied psychological closure by indicating that the user had finished with choosing items and wanted them sent. The initial design also had required a confirmatory click, whereas the new design did not impose an additional click on the user; the key-click count had typically decreased by one. With the new design, users could still form a habit of choosing their usual location from the location list and, on the rare occasions this option was desired, might sometimes forget to specify that they wanted the order sent elsewhere. However, even with this potential fault, the new design was a major improvement over the previous one. |
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