Genres are defined by the presence and number of genre-associated elements. Some elements strongly shift a world towards a certain genre. Others only weakly contribute to a genre but do little to define it in isolation. As examples, magic is a strong fantasy-associated element – its presence strongly indicates a fantasy world. Swords are a weaker element, often present but not as definitive. Some elements, like cults or ruins, are more universally accepted across genres. These universal elements can be inserted into fantasy worlds, science fiction worlds, post-apocalyptic worlds, superhero worlds, steampunk worlds, and others and still feel like a natural addition to the setting.

While it’s tempting then for worldbuilders to treat genres as a checklist of elements to include, the reality is more complex. Genres are fluid and multifaceted, shaped by their combination of elements rather than a rigid adherence to any particular list. While specific elements often characterize a genre (such as magic in fantasy worlds), their presence or absence alone doesn’t definitively determine it (a fantasy world can still be fantasy even without magic). Rather, genre is often determined simply by an ambiguous mental tally of all strong and weak genre-associated elements, the sum of which then determines the genre.

Importantly for worldbuilders, this means that individual elements can be added to or subtracted from a fictional world without impacting its genre as long as enough other genre-associated elements remain. Cases are rare where a single specific element is absolutely required for a genre to be a genre. This allows worldbuilders to craft unique and novel worlds using different combinations of elements that are still undeniably of a particular genre. Elements can also be adapted to suit other genres. For example stereotypical dragons are a fantasy-associated element. However their inclusion within a science fiction world is not prohibited (imagine dragon-like creatures terrorizing explorers on an alien world).