We geeks sometimes focus on how realistic a setting is: Historic or Contemporary settings should be completely realistic, Speculative settings can include hypotheticals as long as they don’t violate known scientific laws, and Fantastic settings just don’t care. But judging which made-up elements are truly speculative is pretty subjective and subject to change, so it’s kind of a useless category.
What I think actually matters is not whether there are any made-up elements that are central to the setting, or are any such elements merely incidental. Do the players have to understand how the unreal things work, or have to deal with them in any way?
If there are no unreal elements, or any unreal elements have no real effect on player decisions, the setting is Mundane. A straight historical game would be Mundane, but so would a time-travel game, if the time-travel method is just an excuse to play in multiple time periods and the players can’t play tricks with time travel to solve problems (See: Quantum Leap.) Similarly, it could include adventures in space, if the space travel is just a gimmick to get characters off world and the destinations are very naturalistic.
Another example would be flavor that fits the supernatural beliefs of a bygone era, but which has no effect on events: witches making a prophecy for Macbeth, but which can be explained away as self-fulfilling prophecy.
If there are unreal elements that directly challenge the player characters, or that the player characters can use to deal with challenges, the setting is Fantasy. This covers everything unreal: magic, super powers, super science, aliens, monsters. If the fantasy elements are truly over-the-top, they can be called Cosmic instead, but it’s not strictly necessary.
These setting types can be seen through a variety of filters or moods:
- Adventure: The characters are on an equal footing (or nearly so) with the challenges they face
- Horror: The characters are outclassed by the challenges they face and may be killed, or worse
- Comedy: The characters are at the mercy of the challenges they face, but are unlikely to be killed or significantly harmed
I wouldn’t merge the filter with the classification abbreviation, but would just add it to the end. Thus, we have:
- Class and Level Action Mundane (CLAM) Adventure: Historic or Contemporary combat or survival games
- Class and Level Exploration Fantasy (CLEF) Adventure: D&D
- Skill and Talent Investigation Fantasy (STIF) Horror: Call of Cthulhu and similar horror-mystery games. CoC could be called STIC instead, if desired.