One of the ideas that dominates my thinking about game design is the distinction between two completely different kinds of thinking. There is a dichotomy fundamental to our universe and our thinking. It takes many forms and has been described with different terms in different fields of endeavor. In linguistics, we call it “noun versus verb”—the two fundamental components of language. The noun is the static, the item of existence, the entity, while the verb is the action, the process, the dynamic.

Economists refer to the same idea as “goods versus services.” Physicists know it by “particle versus wave.” Theorists of military science talk about “assets versus operations.” Computer scientists think in terms of “data versus processing,” or “bytes versus machine cycles.” On the Internet, itʼs “storage versus bandwidth.”

There is nothing fundamentally superior about one view or the other, but in some situations one of these two styles of thinking enjoys higher utility. Itʼs a lot easier to think of a person as a noun, a thing, an object, than as a “human being”—an “act of existence of the human kind.” Itʼs also easier to think of a computer program as a set of verbs (instructions) than as a collection of numbers that represent those actions.

But sometimes the two ideas mix maddeningly. Physicists have this problem with photons (particles of light). Is a photon a particle or is it a wave? It surely behaves like a particle when it knocks an electron loose from an atom, but it also acts like a wave when it diffracts through a slit. Which is it?

Or consider the profound conundrum that assaults every economist at a hamburger joint: is the hamburger he purchases a good or a service? Is he purchasing beef on a bun or the service of cooking the beef and delivering it fresh to him? You could lose your dinner over this vexing problem.

The significance of all this becomes clear when we consider the nature of interactivity. One of the fundamental characteristics of interactivity is choice. Without choice, there can certainly be no interactivity. But what is the nature of choice? We often think of choice in terms of a menu: should I have the smoked salmon, the medallions of lamb, or the Double Cheese Monster Burger? When we think of it this way, it seems that choice is a list of nouns. But thatʼs not truly the nature of our choice: the true choice is between buying the smoked salmon, buying the medallions of lamb, or buying the Double Cheese Monster Burger. Choice is a selection among actions, not a selection among things.

Thus, every interactive process provides the player or user with a set of verbs from which to choose. Do I press the “m” key or the “r” key while Iʼm using my word processing document? When Iʼm browsing the web, do I want to take this link or take that link? When Iʼm playing a game, do I shoot the monster or duck for cover? Do I run away or blast away? Itʼs verbs that lie at the heart of everything that we do with computers. We can turn this around and use verbs to characterize any game or, for that matter, any piece of software. If you examine a game and write down all the verbs available to the player, then give that list of verbs to me, I can tell you exactly what that game is about just from the list of verbs. Thus, the verb list provides us with an architectural skeleton for games. Boil a bunch of games down to their verb lists and you have an excellent way of organizing them into a taxonomy. Just as biological taxonomists learned to ignore prominent but uncharacterizing features of various animals, concentrating instead on fundamental structural details such as the shape of the pelvis, so too must scholars of game design concentrate on the properties that matter: the verbs. Ignore such extrinsic details as graphics, sound effects, animation, and so forth; strip away the showy fur, feathers, and skin and look at the skeleton of the game. Thus will you obtain a clearer view of the reality of the game.

Another useful exercise is to consider the size of the vocabulary of the game (or software product). The old Atari 2600 games had five basic verbs: “go left,” “go right,” “go up,” “go down,” and “fire.” Modern games have expanded on this core repertoire, but they still retain a tight verb set. This is usually accomplished by conflating verbs. One does not bother to “pick up” an object lying on the floor; the mere act of moving over that object suffices to pick it up. One does not explicitly open a door; the simple act of moving into it accomplishes the job. In many shooters, one controls the direction of motion, the line of sight, and the line of fire with just two basic verbs: “turn left” and “turn right.”

We must be careful to differentiate between verbs and direct objects in such censuses. A single verb that allows us to select a typeface in a word processor may offer one hundred different typefaces, but that does not constitute one hundred different verbs; it is one verb with one hundred direct objects.

A characterization of software products by vocabulary size can illuminate a great many questions. The cleanest, simplest, easiest to learn games always have fewer than ten verbs. Typical games these days have between ten and twenty verbs. Big games, especially strategy games and flight simulators, offer several dozen verbs, and a few monsters tip the scales at a hundred verbs. And full-scale application elephants such as Microsoft Word shake the earth with their lumbering collections of several hundred verbs, only a few of which most people ever learn.

It is also instructive to examine the history of vocabulary sizes. The general trend is simple: a game genre starts off with a small vocabulary, which slowly grows as competitors attempt to one-up each other. As the vocabulary expands, new buyers are discouraged and sales fall. Then somebody comes up with a leap forward that permits them to fall back to a smaller vocabulary. Sales soar, a star is born, and then the copycats differentiate themselves by adding new verbs to the basic vocabulary.

Another interesting line of research is to examine vocabulary sizes by genre. In general, shooters and fast action games will have the smaller vocabularies, while strategy games and flight simulators will have the larger vocabularies. A careful examination of these trends can reveal much about the nature of the games.

The distribution of verb usage also provides some interesting insights into the nature of software. Clearly, some verbs will be used more frequently than other verbs—what are the ratios of usage between the most frequently used verbs and the least often used verbs? If an uncommon verb is used, say, 1,000 times less frequently than the most-used verb, does that suggest that the rarely-used verb is superfluous? Should not the best games maintain a fairly even distribution of the usage of verbs, so that every verb that the player takes the trouble to learn provides the same amount of actual gameplay? Conversely,would a game heavy with seldom-used verbs prove too onerous for most players?

Conclusion: to see the true nature of any piece of software, ask, “What does the user DO? What are the verbs?”