2016-06-07 : Core Tension
In Chess, the object of the game is to checkmate the other king, but you might not be able to do it. This is because you can move your pieces only in certain ways, arranging a checkmate requires some pretty complicated coordination, and your opponent is not only actively resisting, but is trying to checkmate you too, the whole time.
This is the "core tension" in Chess. "The object of the game is to __, but you might not be able to do it, because __."
What's the core tension in your game?
From this point of view, you can say that "a game" is an elaboration of its core tension, and that when you enact it, "gameplay" spills out.
You can compare games to see whether they have identical, similar, or different core tensions, and also how they elaborate their core tensions into similar or different games. You can see how small differences in core tension and elaboration can create large differences in gameplay, and how similar gameplay can spill out of radically different core tensions, if that's how they're elaborated. Examples: Chess vs Tafl, Hearts vs Spades vs Knaves, Eat Poop You Cat vs Pictionary.
You can peer into a core tension to see the lines across which it's tensed. Some games are easy or inevitable, some are impossible. Some call for gambling, some for patient problem-solving, some for the right strategy, some for followthrough. Some are easy if you approach them one way but impossible if you don't realize the trick. Examples: jigsaw puzzles, Eat Poop You Cat, High Five the ISS, Golf (the card game), Are We In the Game?, Perplexus.
You can examine and judge how well a game's elaboration suits its core tension. In some games, the winning way to play isn't the most fun way to play; in other games, it is. In some games, the winning way to play isn't the intuitive way to play; in other games, it is. Examples: Roborally, Go, Pandemic, Mobile Frame Zero, Kodama.