View source for Irreversible Events

[[Category:Patterns]]
[[Category:Action Patterns]]
[[Category:Needs revision]]
[[Category:Dynamic Patterns]]
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[[Category:Needs examples]]
''Events whose effect on the game state cannot be undone.''

All events in a game affect the game state but many may be countered by another events, e.g. a movement in one direction may be countered by a movement in the opposite direction. Game state changes that cannot be revert back in this way are the effects of [[Irreversible Events]]. These type of events guarantee that the gameplay progresses according to a certain design and may be used to clearly indicate changes in what is the current focus of the gameplay to players and, if the player can choose to do the actions that cause the events, can give players more meaningful choices. 

=== Examples ===
Pushing a box into a corner in [[Sokoban]] is an [[Irreversible Events|Irreversible Event]] since the box cannot be moved from there, as the boxes can only be pushed and not pulled.

The Ko (and meta Ko) rule in [[Go]] is used to make it impossible for the game to run into infinite loops and without these some events in the game would be reversible.

== Using the pattern ==
To really enforce that events are irreversible in games they need to have [[Dedicated Game Facilitators]], including [[Game Masters]] (but the latter may also make this assumption invalid). Other games may have them in the rules but these may not be followed. 

Even though [[Real-Time Games]] make it impossible to undo actions (without resorting to [[Save-Load Cycles]] or [[Game Time Manipulation]]) this does not automatically create [[Irreversible Events]] since later action may cancel the effect of earlier ones. Making events into [[Irreversible Events]] can be done by making sure that all other events in the whole game design do not affect a specific part of the game state (other events may affect that part of the game state as long as all affect it in the same way or direction). Other ways of making [[Irreversible Events]] are to make actions use [[Non-Renewable Resources]] (in which case the action rather that the consequences of the action may be [[Irreversible Events]]) or create events that give players information. Designed [[Surprises]] are thus a form of [[Irreversible Events]], and since they are a form of [[Trans-Game Information]], they are even [[Irreversible Events]] across game sessions. Events that provide [[Strategic Knowledge]] are likewise [[Irreversible Events]] since these also generate [[Trans-Game Information]].

[[Irreversible Events]] can be instantiated in many different forms. [[Alarms]], [[Controllers]], and [[Switches]] are game elements that can be used to enforce [[Irreversible Events]], in the first case by not being able to be activated more than once or having effect that remain even when they are activated again, and in the second case by not being able to be deactivated once activated (or vice versa). A typical example of a class of [[Irreversible Events]] is [[Leaps of Faith]], which forces players to dedicate themselves to a certain movement in the game. [[Quick Travel]] is another type of movement that easily can be an [[Irreversible Events|Irreversible Event]] if one cannot come back to the old space - the most common example of this is probably being moved to one [[Levels|Level]] after completing another with no possibility of returning. Making the [[Transfer of Control]] of [[Resources]] into [[Irreversible Events]] is part of creating [[Non-Renewable Resources]]; choices regarding [[Character Development]] or [[Upgrades]] are examples of this (the latter is one way to modulate [[Sockets]]). 

Using [[Irreversible Events]] in conjunction with [[Loyalty]] or the creation of [[Enemies]] is a way of creating parts of [[Narration Structures]]. Revealing oneself as a [[Traitors|Traitor]] or committing a noticeable [[Betrayal]] are both examples of [[Irreversible Events]] since they make players change their allegiances (and even if they later change back this will very likely permanently lowered their reliability). These latter types of events, which reveal aspects of what kind of [[Characters|Character]] a player is portraying, can be explicitly designed as [[Character Defining Actions]] and by performing them they become [[Irreversible Events]]. In this way, [[Irreversible Events]] can modulate how a [[Characters|Character's]] [[Open Destiny]] evolves during gameplay.

[[Irreversible Events]] can be created to be the consequences of actions but the actions themselves do not have to be irreversible - their effect may be since partly or completely prevented if they are [[Interruptible Actions]]. Likewise, actions that cause [[Ultra-Powerful Events]] do not have to be [[Irreversible Events]] since other [[Ultra-Powerful Events]] may counter the event after it is completed. An example of this is [[Shrinking Game Worlds]]: these are usually [[Ultra-Powerful Events]] that cannot be affected while they are occurring but after the [[Game Worlds|Game World]] has become smaller it may at a later stage expand again.

One of the possibilities of [[Irreversible Events]] is that they can function as [[Closure Points]] since after they have occurred one can know that some parts of the game state are irrelevant for future gameplay.

[[Irreversible Events]] can exist in weaker forms. One case is in games with the possibility of [[Saving]], since this makes it impossible to have totally [[Irreversible Events]] if players are willing to make use of [[Save-Load Cycles]]. This can be countered to a certain extent by causing actions to have [[Delayed Effects]] (c.f. [[The Witcher]]) at the cost of [[Predictable Consequences]]. Another way of having weakly [[Irreversible Events]] is if there are certain [[Privileged Abilities]] that can reverse the effect of the events; one example of this relates to ''cursed'' [[Equipment]] in that equipping them are [[Irreversible Events]] unless some ''remove curse'' effect can be activated. [[Equipment]] in [[World of Warcraft]] that become "Soulbound" when equipped is another example - this makes it impossible to later use them in [[Trading]] and by doing so avoids one form of [[Purchasable Game Advantages]] in the game.

== Consequences ==
Every [[Irreversible Events|Irreversible Event]] that a player understand to be irreversible is a closure. Although this can indicate progress or failure clearly, the presence of the pattern may negatively affect [[Experimenting]] since there is no [[Reversability]], and make [[Puzzle Solving]] more difficult. Rather, the presence of [[Irreversible Events]] promote [[Stimulated Planning]] and may cause [[Analysis Paralysis]] in [[Multiplayer Games]] that are also [[Turn-Based Games]].

[[Irreversible Events]] are required to progress [[Narration Structures]] and can be used to provide a condensed history of gameplay in a game session without losing any events that affected the final outcome. Leaving a [[Levels|Level]] and not being able to come back to it is an example of how a [[Narration Structure]] can be maintained by [[Irreversible Events]]. An example of how [[Irreversible Events]] can advance the [[Narration Structure]] in [[Real-Time Games]] without relying on [[Levels]] is to move the places where [[Spawning]] occurs.

The synthesis of having a [[Freedom of Choice]] between several [[Irreversible Events]] is one way to create [[Internal Conflicts]].

For cases where a [[Construction]] is an [[Irreversible Events|Irreversible Event]], this can provide an increased [[Value of Effort]] to the [[Construction]] since players do not need to worry about them being destroyed.

Quite naturally, [[Irreversible Events]] are incompatible with [[Free Game Element Manipulation]] although this may break game rules. Given that [[Game Masters]] decide what the rules are, these may whenever they wish reverse events while simultaneously change the rules (they may of course enforce the effect of events as they wish also).

== Relations ==
=== Can Instantiate ===
[[Closure Points]], [[Enemies]], [[Internal Conflicts]], [[Narration Structures]], [[Stimulated Planning]]

==== with [[Construction]] ====
[[Value of Effort]]

==== with [[Multiplayer Games]] and [[Turn-Based Games]] ====
[[Analysis Paralysis]]

=== Can Modulate ===
[[Alarms]], 
[[Character Development]], 
[[Construction]], 
[[Game Worlds]], [[Levels]], [[Loyalty]], [[Open Destiny]], [[Puzzle Solving]], [[Shrinking Game World]], 
[[Sockets]], 
[[Spawning]], [[Transfer of Control]], [[Ultra-Powerful Events]]

=== Can Be Instantiated By ===
[[Betrayal]], [[Character Defining Actions]], 
[[Controllers]], 
[[Dedicated Game Facilitators]], 
[[Equipment]], 
[[Game Masters]], 
[[Leaps of Faith]], [[Non-Renewable Resources]], [[Quick Travel]], 
[[Switches]], 
[[Surprises]], 
[[Traitors]], 
[[Trans-Game Information]]
[[Upgrades]], 
[[Upgrading]]

=== Can Be Modulated By ===
[[Interruptible Actions]], 
[[Privileged Abilities]]

=== Possible Closure Effects ===
-

=== Potentially Conflicting With ===
[[Experimenting]], [[Free Game Element Manipulation]], 
[[Game Masters]], 
[[Save-Load Cycles]]

[[Predictable Consequences]] when [[Irreversible Events]] pattern is used together with [[Delayed Effects]] 

[[Purchasable Game Advantages]] when the pattern is used together with [[Equipment]]

== History ==
An rewrite of the original pattern named [[Irreversible Actions]] in the book 'Patterns in Game Design' (Björk & Holopainen, 2004).

== References ==
Björk, S. & Holopainen, J. (2004) Patterns in Game Design. Charles River Media. ISBN1-58450-354-8.