Many of Borges's best-known stories deal with themes of time ("The Secret Miracle"), infinity ("The Aleph"), mirrors ("Tlön, Uqbar, Orbis Tertius") and labyrinths ("The Two Kings and the Two Labyrinths", "The House of Asterion", "The Immortal", "The Garden of Forking Paths"). Williamson writes, "His basic contention was that fiction did not depend on the illusion of reality; what mattered ultimately was an author's ability to generate "poetic faith" in his reader."
His stories often have fantastical themes, such as a library containing every possible 410-page text ("The Library of Babel"), a man who forgets nothing he experiences ("Funes, the Memorious"), an artifact through which the user can see everything in the universe ("The Aleph"), and a year of still time given to a man standing before a firing squad ("The Secret Miracle"). Borges told realistic stories of South American life, of folk heroes, streetfighters, soldiers, gauchos, detectives, and historical figures. He mixed the real and the fantastic, fact with fiction. His interest in compounding fantasy, philosophy, and the art of translation are evident in articles such as "The Translators of The Book of One Thousand and One Nights". In the Book of Imaginary Beings, a thoroughly researched bestiary of mythical creatures, Borges wrote, "There is a kind of lazy pleasure in useless and out-of-the-way erudition." Borges's interest in fantasy was shared by Bioy Casares, with whom he coauthored several collections of tales between 1942 and 1967.
Often, especially early in his career, the mixture of fact and fantasy crossed the line into the realm of hoax or literary forgery.[Note 6]
"The Garden of Forking Paths" (1941) presents the idea of forking paths through networks of time, none of which is the same, all of which are equal. Borges uses the recurring image of "a labyrinth that folds back upon itself in infinite regression" so we "become aware of all the possible choices we might make." The forking paths have branches to represent these choices that ultimately lead to different endings. Borges saw man's search for meaning in a seemingly infinite universe as fruitless and instead uses the maze as a riddle for time, not space. He examined the themes of universal randomness ("The Lottery in Babylon") and madness ("The Zahir"). Due to the success of the "Forking Paths" story, the term "Borgesian" came to reflect a quality of narrative non-linearity.[Note 7]
The philosophical term "Borgesian conundrum" is named after him and has been defined as the ontological question of "whether the writer writes the story, or it writes him." The original concept put forward by Borges is in Kafka and His Precursors. After reviewing works that were written before those of Kafka, Borges wrote:
If I am not mistaken, the heterogeneous pieces I have enumerated resemble Kafka; if I am not mistaken, not all of them resemble each other. The second fact is the more significant. In each of these texts we find Kafka's idiosyncrasy to a greater or lesser degree, but if Kafka had never written a line, we would not perceive this quality; in other words, it would not exist. The poem "Fears and Scruples" by Browning foretells Kafka's work, but our reading of Kafka perceptibly sharpens and deflects our reading of the poem. Browning did not read it as we do now. In the critics' vocabulary, the word 'precursor' is indispensable, but it should be cleansed of all connotation of polemics or rivalry. The fact is that every writer creates his own precursors. His work modifies our conception of the past, as it will modify the future."