"I have more souls than one," wrote Fernando Pessoa, a Portuguese poet who created more than seventy-five alter-egos (he termed them heteronyms) before he died in 1935. More than merely creating them, Pessoa gave each of his soul's names, personalities, backstories, poetic voice and even deaths. His theory of souls was simple:

Each of us is several, is many, is a profusion of selves. So, the self who disdains his surroundings is not the same as the self who suffers or takes joy in them. In the vast colony of our being, many species of people think and feel in different ways.
From Fernando Pessoa's The Book of Disquiet

Until the end of the 19th century, the concept of a soul in literature and philosophy was dominated by a single soul theory tied closely with Christian morality: the devil's deal in Christopher Marlow's Dr Faustus or Oscar Wilde's The Portrait of Dorian Gray. The soul was something humans were bestowed and protected until it passed on to heaven.

But in the 19th century, the thematic landscape began to change. Culminating in Jung's theory of the soul as experience, unique to each human, and highly complex—i. e. soul as personality. No longer endowed by the Almighty, the soul was intensely human, even mortal, and our body was both creator and host. Thus, Pessoa's breaking up the soul into two or even seventy-five distinct entities—although pretty daring for his time—is nothing more to a contemporary reader than a profoundly imaginative writer considering aspects of one person.

Brazilian writer Joaquim Maria Machado de Assis (June 21, 1839 – September 29, 1908) explored multiple souls - although there were perhaps more like identities - in a short story in his 1881 collection The Looking-Glass: Essential Stories.

Illustration by Federico García Lorca, a Spanish poet with a short but explosive writing career exploring the duality of life, death, hope, and disillusionment. He was shot by Spain's fascist Government in 1936 for his poetry and homosexuality.

Machado de Assis's writing predated both Pessoa and Jung, but his position was similar to theirs. The narrator in The Looking Glass tells us the soul is a factor of two: internal and external.

Every human creature has two souls: one looking from the inside outward, and the other from outside in... The external soul can be a spirit, a fluid, a man, several men, an object, or an operation. There are cases, for instance, where a simple shirt button is somebody's external soul, and likewise the polka, a game of ombre, a book, a machine, a pair of boots, a cavatina, a drum, etc. It is clear that the role of this second soul is to transmit life, like the first; the pair of them complete the man, who is, metaphysically speaking, an orange...These are potent, exclusive souls, but others, however potent, are changeable in nature.

Machado de Assis creates a dichotomy of internal existence and external validation. The things we think we are and the things in which we see ourselves reflected. The narrator continues to describe how the external soul, in particular, can and does change.

There are certain gentlemen, for example, whose external soul, in their early years, was a rattle or a hobbyhorse and, later, one might suppose, some charitable body. As for me, I know a lady - truly, a very dear one - who changes her external soul five, six times a year. During the season, it is the opera; when the season ends, that external soul is replaced by another: a concert, a Cassino dance, the Rua do Ouvidor, the town of Petrópolis.

Jung's theory of the personality states that the soul is a melting pot of experience and memory. Machado de Assis even calls them "natures," and in the story, the profession of the man (external nature) does away with the man (internal nature).

For a few days, the two natures remained in balance, but it was not long before the primary one yielded to the other; only the last part of humanity was left. It then happened that my external soul, which was formerly had been the sun, the air, the countryside, and the eyes of girls, changed in nature to become politeness and bowings and scrapings of the household, everything that spoke to me of the position, nothing that spoke of the man. Within three weeks, I was transformed.

The character's new identity is based on the external soul. He takes a position as an ensign in the National Guard; as long as he is in the uniform, he feels complete. But when left alone, he cannot understand who he is without reconnecting the internal and external souls.

"Ever since I was left alone, I had not once looked in the mirror. My abstention had not been deliberate; there was no reason for it; it was an unconscious impulse, a fear of finding myself one person and two in that solitary house, and if that explanation is true, nothing could be better proof of human contradiction, because, after eight days, I had the notion of looking into the mirror with that very purpose, of finding myself... But the nature of my situation was such that I could not even feel fear, or at least not fear as it is commonly understood. What I felt was something inexplicable. I was like a dead man walking, a somnambulist, an automaton. When I slept, that was a different matter. Sleep brought me relief, not for the common reason of its being the brother to death, but for another. I believe I can explain the phenomenon thus: sleep, by eliminating any need for an external soul, allowed the inner soul to act.

Joaquim Maria Machado de Assis. Photograph by Marc Ferrez.

Argentine writer Jose Luis Borges once wrote a short story called Borges & I about two personas in the same body. Borges was afraid of mirrors his entire life because he might be confronted by a separate image of himself, the double. And yet, in Machado de Assis, the mirror in the story connects the man back to himself. Do mirrors tell us who we are? Does our concept of self reside in this external and internal vision bonded in the mirror? Read more on how we see ourselves reflected and identified, the effects of inheritance on identity, Gaston Bachelard's mid-20th-century masterpiece of space and the concept of self.