Causality is the relationship between two events, where one event is the cause and the other is the effect. I punch you, and as a result, you hurt.
Of course, Causality isn't always that cut and dried, especially in gaming:
Time Travel raises questions of causality. Can the effect eliminate the cause? Can you travel back to before I punched you, and ambush me? If so, do you still hurt? Can I got back before that and punch you first again? See also Novikov Self-Consistency Principle, Stable Time Loop, Branching Time Travel, and Temporal Paradox. If time travel gets out of hand, it leads to Collapse of Causality.
FTL (in the form of a star drive, FTL communication, or just Teleportation ) creates similar issues, because FTL is, in effect, a limited form of Time Travel. (Scientifically, FTL is Time Travel, but as presented in most Sci-Fi, it's just Hyperspace or SuperSpeed). Think of two starships. The first ship sends an FTL distress signal because it's engines are on fire. The second ship, getting the signal from several light years away, uses it's FTL drive to go rescue the first ship and put out the fire. The second ship then returns to it's own original location, and the crew aims a telescope in the direction the distress signal had come from. If they wait long enough for the light to travel, they will eventually see the first ship with it's engines on fire. It looks for all the world like that ship is still on fire, but clearly it's not, because they've already saved it. See also Relativity and Frame of Reference.
Sometimes, things happen because the plot demands it. Movies and TV can get away with this a little easier than gaming. This is because films often make us a passive viewer, we watch and gawk rather than react and ponder. The hero in a movie can make a mistake (miss a clue, trust the wrong person, not consider an obvious solution) that the viewer wouldn't. In an RPG, you're actively processing the setting. Getting a player to ignore an obvious solution tends to be difficult, and can undermine willing suspension of disbelief.
In gaming, causality can exist between rules and setting. For an example consider any RPG that lacks morale or fear effects. If the causality goes from the rules to the setting, it could be common for mooks to fight to the death, and never surrender or flee. That's very different from the real world, where battles are often won because of retreat or panic, and desertion is a frequent topic of concern for military leaders.
Now suppose the causality flowed the other direction, and the rules were just considered an attempt to simulate the setting. In that case, the GM might decide to play the NPC mooks more realistically, having them sometimes flee or panic even when the situation remains winnable, even though the rules make no provision for it. Some GMs might even build their own morale house-rules for a game that had lacked such things. Then it's like causality flows from setting to rules and back again, adjusting the rules to match the setting.
Another example might be falling. If falling 100 feet does 10d6 damage, and my PC has 61 hit points, I know I'll survive the jump off this cliff. In the real world, it'd be unlikely anyone would ever be that certain of surviving a fall. If the causality is from rules to world, though, the PC can make that analysis and take the plunge without worry. If it flows from world to rules, the GM might tweak things to make sure the face-plant onto rocks retains lethality. Of course, that opens a can of worms in regards to trust. If the rules say I live, but GM fiat says I died, then why do we have rules in the first place?
Likewise, causality can exist between setting and logic. Let's say you're running a game based on Superheroes. Do you play the genre straight, in full four-color glory, or explore it's grittier deconstructed sides, ala The Watchmen?
If you're running a Star Trek game, do you keep the episodic Planet of Hats and Monster of the Week themes, or enforce continuity from session to session?When the crew solves this session's dilemma by reversing polarity on the engines and creating a portal to the past is this a one-time event, or is limited Time Travel now a part of their recurring arsenal? And thus we've come full circle.
I go back in time to punch you before you can go back in time to punch me for going back in time and punching you for going back in time and punching me for going back in time…
Game and Story Use
- Having an understanding of how the causality flows in the game you're playing (or GMing) can lead to better gaming. You'll be less likely to have a disconnect or nasty surprise that sours the game.