The earliest philosophy of fiction begins before anyone called it that. Ancient myths, epics, and dramas were already using invented stories to explore such topics as gods, fate, and moral failure. Fiction as a philosophy started the first time someone asked, “Is that really true?”
In the East, fiction was used to explore concepts in wisdom literature. In the West, the clearest philosophical turn comes in ancient Greece with the idea of mimesis, or imitation. Plato worried that poetry and drama could mislead the mind. For him, fiction had a danger: it could stir emotion, deepen illusion, and make shadows feel like reality.
Aristotle answered with a more generous view. In the Poetics, he argued that poetry can be more philosophical than history because history tells what happened, while poetry shows what could happen according to probability, character, and consequence. That is the classic starting point.
In the medieval worlds, myth, scripture, and the like often blended together. Stories were often used as vehicles toward another aim including teaching wisdom, theology, and virtue. Allegorical interpretation became especially important. A story could be read beyond its literal surface meaning. This set in stone the idea that a story does not have to be factually literal to carry some truth.
In the modern period, the rise of history, science, and journalism sharpened the distinction between fact and fiction. Fiction became more clearly understood as invented narrative. At the same time, novelists and philosophers kept noticing that fiction could reveal human nature in ways bare facts often could not.
In contemporary philosophy, the discussion becomes more technical: fictional worlds, fictional truth, possible worlds, narrative identity, propaganda, and the ethics of representation. TST enters this story with Imaginative Realism: fiction is not reality denied, but reality recombined.