Hauntology, or spectral studies (which is an even cooler name), is hard to define, in the sense that multiple people have used the term to mean different things. We could say it's the study of the continued existence of things that should be dead, in other words, the study of hauntings.
I just think there's something beautiful about this notion, and it's one of those concepts where after you learn about it you can't really stop seeing it.
There's a saying that the way to be rich in the UK is having an ancestor who was friends with William the Conqueror, there's the fact that the size of roads was governed by the size of carriages, which affected the size of railroads, which ultimately affected the size of the Space Shuttle's Boosters.
When the Far-Right marches in Portland, a city where 2% of the population is Jewish, and chants "Jews will not replace us", it's the USA being haunted by the spectre of nazism.
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In many ways, studying tradition is hauntology, for the people responsible for some customs are long dead, and their reasons long gone.
Another way to define hauntology is the notion that the present is haunted by lost futures, it's retro-futurism, it's yestermorrow. It's the aesthetics of the Incredibles and the latest Fantastic Four. It's Gibson's "The Gernsback Continuum".
When you remember your childhood dreams, when you read a love letter to an ex, when you play a few notes in the guitar you used to play in your band in high school, and think about what could have been, that too is hauntology
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For a lovely talk about it and its connection to roguelike games I would recommend this, from last year's Roguelike Celebration.
I titled this post hauntology 01, maybe I won't write about hauntology again, in that case the 01 too will be hauntology.