Metaphysics
In philosophy, the term "metaphysics" refers to universal laws governing the structure of reality. Borges comments on and imagines various fictions of metaphysics in order to compel the reader to more closely examine the fabric of reality.
Labyrinths
Labyrinths show up repeatedly in Borges' stories, particularly in his collection The Garden of Forking Paths. These labyrinths are not always literal in their meaning: for example, in A Survey of the Works of Herbert Quain, the labyrinthine nature of The God of the Labyrinth appears to come more from the structure of the book's false ending than the actual substance of the plot (108).
As a symbol, the labyrinth is ideal for tackling concepts of free will and fate, which Borges is fond of treating. From within a labyrinth, it is virtually impossible to conceive of the maze's overall structure; one can take many different paths which lead to the same place, even if there are some dead ends. It is also unclear when one exits the labyrinth if that was the only exit, or if different paths lead to different exits. These notions of alternate paths with intersections and potentially inevitable outcomes enable one to meditate on what precisely our ability to choose accomplishes, and if free will and fate are mutually exclusive.
Identity
How are we able do determine what something is, and distinguish that thing from others? Borges routinely plays with notions of what makes something unique, as exemplified in A Survey of the Works of Herbert Quain, the plot of which concerns Herbert Quain trying to write Cervantes' novel Don Quixote verbatim from his own life experiences. If two authors come to the same words in different ways, is the product the same or different?
Free Will
One component of Borges' labyrinth motif is how significant our capacity to choose is, if it exists at all. A prime example of this is The Lottery in Babylon, where a secret society that spawns out of a lottery ends up dictating all events of the lives of Babylonians. If all of our experiences are the results of external agents - be they other people, God, fate, or quantum mechanics --then do we have free will? Or, is the question not even relevant at this point? Borges routinely creates situations posing questions such as these.
Fate
The other side of free will, typically seen as its antagonist, is the notion of fate, or the design of events by powers external to the person acted upon by said events. An example of Borges' treatment of fate is the story The Garden of Forking Paths, where all the seemingly unrelated events of Yu Tsun's life - his ancestor's manuscript, his being chased by Captain Madden, the loitering boys directing him to Dr. Alberts house - apparently converge upon a single purpose: the murder of Dr. Albert and consequent postponing of an Allied strike. Like the book of Yu Tsun's ancestor, the events of the story appear to have the organization of a riddle, the inevitable answer to which is the murder of Dr. Albert by Yu Tsun (126-7). Against such implications, did Yu Tsun still have a measure of freedom and agency in the murder?
Religious Allegory
Borges frequently tells stories which, on one level, can be viewed as allegorical critiques of religion. Tlön, Uqbar, Orbis Tertius chronicles a secret society that created a world of imagined metaphysics that slowly penetrated the real world and became mistaken for truth. This can be read as a critique of the imposition of religious beliefs on reality under the guise of truth.
Logic
Borges is philosophically well-read, having studied Germans such as Schopenhauer and Leibniz; he makes this clear in his work, as he frequently employs various forms of logic, or mathematical paradigms of thought. Using logical constructions to describe fictional or allegorical worlds also enriches his metaphysical commentary: a key example of this is The Library of Babel, in which he describes the universe as a library, and uses a logical system with two axioms (fundamental truths) in order to put forth provocative proofs about the nature of being.
Foreignness
Many of Borges' stories, particularly in The Garden with Forking Paths, revolve around an outsider interacting with an established culture. Herbert Quain is trying to make the foreign Don Quixote familiar to himself; the foreigner in The Circular Ruins is a stranger to the ruins in which he finds himself, and is a stranger to the god upon whom he must rely to complete his ritual; in The Lottery in Babylon, the reader is the foreigner, and the narrator is explaining his culture to us. This thematic element goes hand-in-hand with the theme of identity: something's identity is most clearly articulated when it is challenged by something which is starkly different from itself.
Metafiction
In the foreword to The Garden of Forking Paths, Borges says, "It is a laborious madness and an impoverishing one, the madness of composing vast books - setting out in five hundred pages an idea that can be perfectly related orally in five minutes. The better way to go about it is to pretend that those books already exist, and offer a summary, a commentary on them" (67). It is to this end that Borges reviews the invented books, or "metafiction," found in The Garden of Forking Paths. In so doing, he is able to powerfully convey complex themes both in the metafiction and his review of the metafiction, without laboring over the finer dressings required in a lengthy novel.
Infinity
In The Library of Babel, the library that is the universe is infinite; in The Circular Ruins, it is implied that all men are the actuated dreams of other men; and an infinite number of realities are discussed in The Garden of Forking Paths (126-127). Borges, in keeping with his other themes, tackles infinity as the absolute extension of nature and the self. Much of his literature is committed to contriving circumstances in which the infinite quality of all things is revealed.
Mirrors
Mirrors are recurrent in Borges' stories - for instance, Tlön, Urqbar, Orbis Tertius begins with a quotation about mirrors, and the illustrated version of The Approach to Al-Mu'tasim was subtitled A Game with Shifting Mirrors (68-9, 82). This is an ideal symbol for treating the theme of identity because mirrors produce illusory copies of those objects which they reflect.
