This is an excerpt from Andrew Rollings and Ernest Adams on Game Design from New Riders Press, available now.

Any game designer should agree that gameplay is the core of the game. Given an ideal world, designers would probably claim that gameplay should be put above all other considerations. And in a lot of cases, were it not for external pressures, these same game designers would attempt to treat the gameplay with the level of importance that it deserves. There's just one problem with this: There is no universally accepted definition of gameplay. Gameplay is an important, if nebulous, concept. Many times during discussions of games, we have heard comments such as, "This has great gameplay," followed by a detailed description of the particular aspect of the game. However, if instead you were to ask the question, "What is gameplay?", most answers would attempt to explain by example. Indeed, explanation by example can be helpful, but it requires that you infer a definition of gameplay by induction. Describing gameplay without using self-reference is similar to trying to explain the concept of red without reference to color. It is difficult to conceive, but not impossible.

There is a reason for this difficulty: The concept of gameplay is extremely difficult to define. Each designer has his or her own personal definition of gameplay, formed from exposure to many examples over the course of a career. Gameplay is so difficult to define because there is no single entity that we can point to and say, "There! That's the gameplay." Gameplay is the result of a large number of contributing elements. The presence, or lack thereof, of gameplay can be deduced by examining a particular game for indications and contraindications of these elements. (These terms are borrowed from medical terminology: An indication is a positive sign that implies the existence of gameplay, and a contraindication is a negative sign that implies that gameplay does not exist.)

Use of Language

In other fields, such as engineering, architecture, and mathematics, the spread of ideas is facilitated by the use of a common language. Each engineer or mathematician knows how to express ideas—even brand-new ideas—in the given language of the craft. The vocabulary and mechanism for expressing ideas is already there, formalized and developed over many years of practical use and theoretical study. As game designers, we do not have that luxury. Although there has been talk of defining a universal frame of reference for game designers, no such lexicon has been attempted in earnest. Any attempts that have so far been made have not gained major acceptance, and there is no real coordinated effort or cooperation between alternate factions (to the best of our knowledge).

This chapter attempts to define gameplay without reference to itself or reliance on examples of itself for definition. That doesn't mean that we won't give examples, but those examples will not serve as definitions. Instead, they will be used in their traditional role to illustrate the definitions previously laid out. This will give us the beginnings of our lexicon of game design. This might or might not become a standard, but it is at least a starting point that we can use to explain our ideas in this book.

Defining Gameplay

Although we briefly discussed (and loosely defined) gameplay in Chapter 2, "Game Concepts," we did so in terms of the player experience. To continue, we examine gameplay independent of the player experience. We examine the core concepts of gameplay, which are invariant with the player. To do this, we need to state a player-independent definition of gameplay. Sid Meier once defined gameplay as "a series of interesting choices." This is an excellent starting point and forms the basis of our definition of gameplay. We take this statement one step further with our formal definition of gameplay:

One or more causally linked series of challenges in a simulated environment.

On the surface, this does not seem that far removed from Sid Meier's original definition (although it's not quite as good of a sound bite). However, our statement is more precise and rigorous. To be fair, it's unlikely that Mr. Meier expected his original definition to be used for anything more than the off-the-cuff comment it was probably intended to be—a statement designed to challenge and spur further thinking on the subject. If this was the case, it certainly had its intended effect and served as an excellent starting point for our definition.

In the original statement, the use of the word series implies a number of sequential events. Although these events follow one another chronologically, there is no implication that they can be linked. For example, lightning strikes tend to come in a rapid succession of bolts, but there is no evidence to suggest that the strike order is anything other than chance. Hence, we need to define specifically that our gameplay events are linked by causality. Note that we do not say anything about whether the multiple series are required to be interlinked. In most cases, they are—for example, the multiple plot threads in an adventure game—but this is not a specific requirement.

The second half of the original definition uses the words "interesting choices." Although this is true, we feel that this is too broad of a definition. Choosing to visit the cinema, deciding what movie to watch, and thinking about whether to have caramel popcorn or salted popcorn is an example of a series of interesting choices, but it isn't an example of gameplay. So we replace this with "challenges in a simulated environment." The reason for the further restriction to a simulated environment should be self-evident: We stop playing when we quit the game.

Why are we using challenges in place of choices? Again, we feel that the word choices is too broad to be particularly useful. For example, we can make a decision to attempt to shoot the attacking robot, to avoid it, or to quit the game and play something else. All three of these are available choices, but only the first two are gameplay decisions. Consequently, we have chosen to use the word challenges because it more accurately describes the type of event that the player is subjected to.

Another example of a choice that is not directly a part of the gameplay is the prevalence of user-defined "skins" in games such as the Quake series and Half-Life. The player can choose any appearance, but it is purely a cosmetic choice and normally has little effect on gameplay (except when unscrupulous players use this to their advantage, either by deliberately choosing a skin that camouflages them too well—for example, in the extreme case, a moving, shooting crate—or by forcing all the opposing players to take on skins that make them more visible, such as pure white). Odysseus faced many challenges on his 20-year voyage to return home to his wife, Penelope, in Homer's Odyssey. Gordon Freeman (and, by proxy, the player) faces many challenges on his quest to escape from the Black Mesa Research Laboratory in Valve's Half-Life. Tetris players face challenges in their attempts to attain a higher score. Even Pac-Man faces challenges in his attempts to eat all the pellets in the maze while avoiding the evil ghosts bent on his destruction.

The use of challenges is not perfect, but it'll do. An alternative to the use of the word challenges that we discussed in the past was ordeals, but this was found to be arguably too restrictive. Ideally, we'd like to use a word that indicates a concept somewhere between the two.

Pure Challenges