The theory goes like this. If we're looking at computer games, when videogame manufacture was first democratised by the appearance of home computers no one had any idea what they were doing so they were forced to invent by necessity. Ideas were thrown together just to see what operated well, or even operated at all. These times I'll describe vaguely as "pre-genre".

Eventually, however, they hardened into solidified idea-clusters which were the modern genres, each with specific characteristics. In fact, if a game failed to fulfil some of these criteria, it could often be dismissed as a bad game, when in reality it was just a bad example of a particular genre and really succeeded as something else.