Introduction

Carl Gustav Jung (1875-1961), a Swiss psychiatrist, had a vast intellectual output. His theoretical work is divided into eighteen volumes in addition to his memoirs in the book Memories, Dreams and Reflections, his fantasies in the Red Book and the Black Books, letters exchanged with friends and thinkers of the time, and the publication of records of seminars given. Differing from Sigmund Freud (1856-1939) concerning the idea of the unconscious, he formulated his own set of explanations about the functioning of the psyche based on empirical material gathered during his work in psychiatric hospitals, in the clinic, and personal experiences. For Jung, in addition to a personal unconscious, there was a broader and deeper instance called the collective unconscious, a source of life and an expression of human history, examples of which are myths.

Jung and his analytical psychology are increasingly well-known in the academic environment and psychotherapy clinics. His work is vast, his life was long, and his circle of friends included important intellectuals of his time. The relationship between Freud and Jung is known as the most important one. From their first meeting, which lasted long hours, their partnership, support, and mutual admiration reverberated like a legend, which is much talked about to this day. According to ^{Shamdasani (2013)}, the stories surrounding the subject insist on the misconception that Jung’s work is an appendix to Freud’s work. This view says that the main source of all Jungian work comes from Freud. However, Jung took the opposite position, stating that many of his reflections were created before meeting the Viennese master and that his inspiration came from various teachers.

According to Shamdasani, the study of the unconscious rested on two large groups, one of which was based on Jean Martin Charcot (1825-1893) and the other on Pierre Janet (1859-1947). Freud studied with Charcot and Jung with Janet, (^{Shamdasani, 2013}), which points to fundamental differences in the work of the two. All these relationships of friendship, work, and research still need to be further investigated in order to better delineate the theoretical path of these important thinkers who marked their time and knowledge about the psyche and psychology.

Théodore Flournoy was one of these important references. He was born in 1854 in Switzerland. Interested in various subjects, he studied literature, mathematics, theology, and medicine (^{Martinez, Alves, Maraldi & Zangari, 2021}). After the break in the relationship between Jung and Freud, which occurred between 1911 and 1913 due to Jung’s reformulation of the concept of libido and his approach to religious phenomena, the relationship with Flournoy intensified.

The bond between Jung and ^{Flournoy began in 1900} when Flournoy was 46 and Jung was still 25. Two important meetings between them took place in Zurich and Vienna. Flournoy died in 1920, and his son stayed in touch with Jung afterward (^{Martinez et al., 2021}).

There is a remarkable relationship between the two from their research into mediumship. Flournoy followed a supposed medium for five years, called Catherine-Elise Müller, and recorded her in his main work From India to the Planet Mars: A Case of Multiple Personality with Imaginary Languages. Jung, having access to the book, used it as a model for his doctoral thesis, also on a case of mediumship (^{Martinez et al., 2021}).

If, at first, the various authors who shaped psychology as a science focused on occult phenomena, parapsychology, and mediumship, it is worth highlighting their use in Jung’s psychological research. The epistemological limits of his work and the importance of his analysis, which was intended to be scientific, promoted the advancement of psychology and in-depth knowledge of the human mind, in particular the unconscious, and more precisely the collective unconscious.

This article aims to analyze, based on the friendly relationship between Flournoy and Jung, how the concepts of archetype and cryptomnesia come closer or further apart throughout their theoretical development. To do this, we carried out a bibliographical survey of the two main works, Jung’s Symbols of Transformation and Flournoy’s From India to the Planet Mars, as well as the theoretical support of other works by Jung that bring concepts and themes into line with our investigation. We also researched the context of the emergence of scientific psychology at the end of the 19th century in articles and theses, as well as the influence of investigations into occult phenomena that took place in different parts of the world, with various focuses, not only religious but also as attempts to understand the human psyche.

The popularization of occult phenomena

Nineteenth-century Europe was marked by an upsurge in the popularization of psychic phenomena, such as the famous spinning tables in séances; mediums who claimed to be able to contact the dead; reports of apparitions of spirits, and strange noises in houses; among others. Also known as occult or paranormal phenomena, they were part of a field of knowledge distinct from the natural sciences that were being developed at the time. Parapsychology was an area of continuous interest for Jung, a fact found in one of the central books of his work, Symbols of Transformation, in which we find his work on the psychological character of Miss Miller’s supposedly mediumistic phenomena (^{Jung, 1911/1912/2011c}).

In order to deal with how mediumistic phenomena influenced Jung’s investigations, we have chosen to first give a brief account of the genesis of these phenomena. Three events that took place in North America between 1837 and 1848 gave rise to the first scientific investigations into mediumship: (1) the case of the Shakers, (2) the case of Jackson Davis; and (3) the case of Hydesville (Vianna, 2002).

The case of the Shakers took place in a community in the United States between 1837 and 1844, in which the members reported being possessed by the spirits of Native Americans. Shortly afterward, the case of Andrew Jackson Davis (1826-1910), who claimed to have extrasensory gifts, emerged in a rural district of New York. A few years later, in 1848, in the region of Hydesville, California, there was the phenomenon of the Fox sisters, who reported having established a dialog with the spirit of a former caretaker who had been murdered in their home. During this period, similar phenomena began to occur in Europe, particularly in France and Germany (Vianna, 2002).

Interested in the psychic phenomena that were becoming popular at the time, two groups emerged to study them: individuals linked to religious knowledge who became part of the spiritist movement that arose from these investigations, and “[...] those who remained exclusively in the scientific line of research into the phenomena, without embracing the religious movement (Vianna, 2002, p. 135)”¹. The first group has as an example the French educator Hippolyte Denisart Rivail (1804-1869), known by his pseudonym Allan Kardec and responsible for organizing the spiritist doctrine and spreading it throughout the West (Vianna, 2002). As for the second group, we have the example of the eminent psychologist and philosopher William James (1842-1910), who considered religious experience and occult phenomena to be essential objects for the emerging scientific psychology:

[...] between 1890 and 1902, James broadened his notion of psychology to include exceptional states of consciousness, especially religious experiences and psychic phenomena. [...] after Varieties² , he continued his investigations into consciousness, mental cures, psychic phenomena and mystical states [...]³ (^{Araújo & Honorato, 2017, p. 11}).

Another important figure was Pierre Janet. In order to understand some of the themes of the emerging psychology, such as the unconscious and dissociations, Janet also delved into mediumistic investigations. Jung studied with Janet, and the latter influenced the former by constructing a classification of the basic forms of mental illness, focusing on split personality, fixed and obsessive ideas, as well as by affirming the need to delve deeper into the unconscious of neurotic patients. Janet was also the first to define the phenomenon of dissociation and complexes (^{Douglas, 2008}). Frederic Myers (1843-1901) also studied telepathy, hypnosis, hallucinations and hauntings. In addition, his greatest contribution to the study of the unconscious concerns the subliminal self, since the conscious self (or supraliminal self), for this author, did not represent the whole mind (^{Almeida & Neto, 2004}). Even Freud openly discussed occult phenomena, such as witchcraft. Influenced by Charcot, in order to understand what happened in hysteria, he went into what would be states of ecstasy and possession (^{Almeida & Neto, 2004}).

Jung follows these same questions. For the Swiss psychologist, “[...] parapsychology would be the science that deals with biological and psychological events, which show that the categories of matter, space and time (and also that of causality) are not axiomatic”⁴ (^{Jung, 1963/2011f, p. 89, § 1231}). Studying hidden phenomena would mean understanding more and more about the psychology of the unconscious.

In addition to these authors, Théodore Flournoy was also interested in the subject. His most famous work is From India to the Planet Mars (1900), in which he makes a case study of a young medium whose pseudonym is Hélène Smith. In this study, he follows some mediumistic sessions in which she, in a trance, says she remembers previous incarnations. There were three incarnations: 1) an Indian princess, 2) the French queen Marie Antoinette, and 3) an existence on the planet Mars. Of the latter, she said she remembered the Martian dialect and information about its physical structure (^{Martinez et al., 2021}).

As we will see below, these thinkers were part of a specific moment in the history of psychology, marked by the spirit of that time.

The birth of scientific psychology

It is worth noting that the European Zeitgeist of the 19th century was the cradle of two investigative movements that would have a substantial impact on 20th-century psychology: the investigation of mediumistic phenomena and the investigation of the unconscious.

Psychology as a scientific project had already taken its first steps in the second half of the 19th century. Its precursors included the aforementioned William James and the physician, philosopher and psychologist Wilhelm Wundt (18321920). Both had the common goal of organizing a field separate from the philosophical-metaphysical speculations and religious interpretations of that time, a field based on science that would be dedicated to investigating human psychological phenomena (^{Abib, 2009}). According to ^{Schultz & Schultz (2019)}, the milestone that established the emergence of the new science was the publication of Contributions to the Theory of Sensory Perception by Wundt between 1858 and 1862, in which he described his original experiments and his proposals for the methods of the new psychology. In 1867, Wundt began the first course in psychology at the University of Heidelberg, consisting of lectures that became a book in 1874, Principles of Physiological Psychology. The German doctor’s masterpiece, Principles was responsible for establishing psychology along the lines of laboratory science, equipped with its own questions and new methods of experimentation (^{Schultz & Schultz, 2019}). Wundt is also credited with creating the first laboratory in the field in 1881 in the city of Leipzig, and a journal dedicated to research into psychology, called Philosophical Studies. His initial intention was to call it Psychological Studies, which was not possible because there was already one with this name focused on spiritism and occultism (^{Schultz & Schultz, 2019}), which reinforces the idea that these subjects were intertwined at the time.

William James, following in Wundt’s footsteps, is considered the forerunner of American psychology. In 1872 he took up the position of professor of physiology at Harvard, and in 1875 he gave his first psychology course at the same university, entitled The Relations between Physiology and Psychology. As a result of this position and his course, James created the first psychology laboratory on American soil (^{Schultz & Schultz, 2019}). Jung, on a trip to the United States with the psychoanalytic delegation that was to present at a conference at the Clark University in 1909, met James and the conversation between the two reverberated in his work (^{Resende & Melo, 2018}). It’s important to note that even when investigating topics such as religiosity and the psyche, James defended the science that was born with scientific methods:

[...] Psychology today is little more than physics was before Galileo or chemistry before Lavoisier. It is a mixture of phenomenal description, gossip and myth, including, however, enough real material to justify the hope that, with discernment and goodwill on the part of those interested, its study may be so organized as to become worthy of the name of natural science at some not too distant day. [...] My wish, in treating psychology as a natural science, was to help it become one⁵ (James, 1892, p. 146, as cited in ^{Araújo & Honorato, 2017, p. 8}).

His investigative method remained aligned with the objective of organizing a psychological science. The way James thought of psychology required the psychologist to have a scientific spirit in the strictest sense, that is, the willingness to relate morosely, without fear or prejudice, to any area in which human phenomena are present. This position can be found in William James, as Araújo and Honorato point out:

For the psychologist, man’s religious propensities must be at least as interesting as any other facts pertaining to his mental constitution. It seems, therefore, that the most natural thing for me, as a psychologist, to do is to invite you to a descriptive survey of these religious propensities. If the investigation is to be psychological, its object must be religious feelings and impulses, not religious institutions⁶ (James, 1902/1985, p. 12 as cited in ^{Araújo & Honorato, 2017, p. 7}).

Therefore, we can see two points in James’ position: (1) by proposing a scientific psychology, he understands the investigation of religious phenomena as a constituent part of the object of the new science; and (2) by proposing the organization of a psychology separated from metaphysical and theological speculations, he also proposes that such phenomena be investigated with scientific rigor (^{Abib, 2009}).

Flournoy can also be cited as a researcher dear to the history of the beginnings of psychology, considered one of the founding fathers of the fields of parapsychology and the psychology of religion. In 1891, the psychiatrist took up the new chair of experimental psychology at the University of Geneva, becoming the institution’s first professor of psychology. The following year, he founded a psychology laboratory there, dedicated to the study of personality along the lines of dynamic psychiatry. Both events constitute a milestone for the birth of scientific psychology since his chair and laboratory were located in the faculty of sciences, and not in philosophy as was customary (^{Martinez et al., 2021}). The historical period in which Flournoy built his research career was marked by psychology’s growing interest in the processes of how the mind works, as well as the different states of altered consciousness. These phenomena were investigated at the time through techniques such as hypnosis, the observation of clinical cases of somnambulism and multiple personalities, and the study of religious experiences. As well as publishing the book From India to the Planet Mars and influencing Jung through this book, Flournoy published books by William James in Europe. He also worked with the hypothesis of the existence of processes subliminal to consciousness, a hypothesis investigated by the aforementioned psychiatrist Pierre Janet and paranormal phenomena researcher Frederic Myers (^{Martinez et al., 2021}).

As for investigations into the unconscious, Freud is considered the main forerunner of the field due to his role as the founder of psychoanalysis, an area whose main objective is to investigate the psychodynamic processes of the mind.

In the first topic of psychoanalysis—published until 1920—Freud conceived of the psychic apparatus as a whole divided into the conscious and the unconscious. The conscious would be made up of contents recognized by the ego, nameable and accessible to thought, and would be subject to the reality principle, that is, the socio-cultural demands of conduct and moderation which, to maintain order and social cohesion, bar the full realization of desire (^{Nasio, 1999}). The unconscious, on the other hand, is subject to the pleasure principle, an incessant movement in search of drive satisfaction through the release of libido. For Freud, the unconscious would be constituted in the process of repression, when conscious experiences are expelled from the conscious by the reality principle, in order to give cohesion and balance to the ego. The formations of the unconscious, such as dreams, pathological manifestations, involuntary acts and excessive emotional relationships, would be modified representations of repressed desires which, if they came to consciousness in their true form, would cause the rupture of the ego, of the constructed image of the self (^{Nasio, 1999}).

In the second topic, with the formulation of the concepts of death drive and life drive, psychoanalytic theory underwent considerable changes; however, the understanding that the unconscious is made up of repressed experiences that were once conscious remained (^{Nasio, 1999}). It was at this point that Freud and Jung diverged in their conceptions of the functioning of the psychic apparatus. As we will see later, for Jung, the descriptive unconscious made up of repressed contents would be called the personal unconscious, and although he assimilated this explanation into his theory, he broke off with Freud when he pointed out the inability to work with certain unconscious phenomena using the theory of repression.

Still on Freud, contrary to popular belief, he was not the first to investigate the phenomena of the unconscious mind. The publication of his first book in 1895, Studies on Hysteria, was part of an investigative movement that was already taking shape in the midst of philosophical speculation that had been going on since the Renaissance (^{Schultz & Schultz, 2019}). The theory of monads by Gottfried Wilhelm Leibniz (1646-1716), the concept of the threshold of consciousness proposed by Johann Friedrich Herbart (1776-1841), the analogy between the mind and an iceberg by Gustav Theodor Fechner (1801-1887) and the motto that the unconscious is the key to the conscious (^{Noé, 2015}) by Carl Gustav Carus (1789-1869) are examples, prior to Freud, of philosophical speculation about the phenomena of the unconscious mind (^{Schultz & Schultz, 2019}). Freud’s central contribution lay in the fact that, based on what had already been discussed, he began to build a scientific method for investigating the unconscious, which made possible the theoretical advances in the psychodynamic processes of the human being throughout the 20th century.

His endeavor was influenced by two prominent thinkers: Charcot and his disciple Janet, as mentioned above. Charcot, as director of the neurological clinic at Salpêtrière, a renowned asylum in Paris for hysterical women, was responsible for bringing the method of hypnosis into the spotlight of psychiatric science at the time, presenting positive results of the method applied to patients (^{Schultz & Schultz, 2019}). Janet, invited by Charcot to open an experimental laboratory in Salpêtrière, was responsible for changing the psychiatry of that time from a somatic to a psychic perspective. The former strove to find a physical cause for abnormal behavior, such as brain lesions and lack of nerve stimulation. The latter strived to find psychological and emotional causalities (^{Schultz & Schultz, 2019}). The hypnosis and cathartic method used by Charcot already contained the essence of the free association method developed by Freud years later. The reform initiated by Janet, on the other hand, represented an anchor point for Freud, since the empirical material for psychoanalytic studies did not come from the traditional laboratory experiments of academia, but from the observation of clinical cases. Freud, as the forerunner of a new investigative method, was responsible for changing the way hysteria cases were thought of at that time, and psychoanalysis can be considered a movement of revolt against the somatic orientation traditionally predominant in psychiatry at that time (^{Schultz & Schultz, 2019}).

All these important thinkers contributed to the birth of scientific psychology. With it, within the strict scientific method that underpinned so many other areas, questions also arose from philosophy, religion, parapsychology and occultism. There was a concern to understand the workings of the psyche and its limits.

Jung and Flournoy, therefore, entered this universe to advance their knowledge of the psyche: Flournoy, with the case of the medium Catherine-Elise Smith⁷; Jung too, with the case study of his medium cousin Hélene Preiswerk⁸ (under the influence of Flournoy’s work). But beyond a religious and mediumistic understanding of the so-called occult phenomena, his interpretation is psychological, as in his account:

[...] the habit of turning the tables eventually freed itself from its beginnings and reached the level of the spiritism of modern belief in spirits, a revival of the shamanistic religions of our ancestors. This development of reactivated contents of the unconscious, which still persists, has led in recent decades to a prodigious expansion of subsequent levels of development, i.e. eclectic gnostic systems, theosophy and anthroposophy and, at the same time, the beginnings of analytical psychology, which has its origins in French psychopathology, especially from the school of hypnotists, and seeks to scientifically investigate the phenomena of the unconscious: the same phenomena that become accessible to the naïve nature of theosophical-gnostic sects in the form of mysteries⁹ (^{Jung, 1918/2011e, p. 23, § 21}).

Two important concepts have been useful in trying to broaden our understanding of the unconscious, which has been discussed in many ways by philosophers and the psychologists mentioned above: cryptomnesia and archetype. Flournoy and Jung have a dialog that doesn’t always coincide. However, from the questioning and dissent, it was possible to arrive at clues as to what would become the Jungian concept of the collective unconscious.

From cryptomnesia to archetype: searching for an unconscious beyond the personal

In his book Symbols of Transformation (^{Jung, 1911/1912/2011c}), Jung analyzes the fantasies of a woman called Frank Miller, investigating what the unconscious might be. Among these fantasies, Jung highlights two of her poems, one entitled Hymn to the Creator¹⁰ and the other The Song of the Moth¹¹ . Concerning the second poem, Frank Miller, differentiating mediumship from other cognitive processes, reflects:

This little poem made a deep impression on me. Admittedly, I didn’t immediately find a sufficiently clear and direct explanation for it. But a few days later, when I wanted to read a philosophical text to a friend that I had read in Berlin the previous winter and which had excited me, I came across the following words: “La même aspiration passionnée de la mite vers l’étoile, de l’homme vers Dieu”. I had completely forgotten them, but it seemed quite clear that these very words had reappeared in my hypnagogic poetry. What’s more, I remembered a drama I saw a few years ago, “La mite et la flamme”, as another possible source for the poem. You can see how many times the expression “moth” was inculcated in me¹² (^{Jung, 1911/1912/2011c, p. 107, § 123})¹³.¹⁴

In other words, for her the theme of the moth appearing in her poetry was justified by the fact that she had had previous contact with this expression, even though she had forgotten it. According to Flournoy, the return of something completely forgotten would be a case of cryptomnesia. He defines this concept as the “[...] reappearance of memories deeply buried under the normal state of wakefulness, together with an indeterminate amount of imaginative exaggeration on the canvas of real facts”¹⁵ (^{Flournoy, 1900, p. 276}).

While researching unconscious phenomena, Jung became interested in Flournoy’s research on mediums and the subject of cryptomnesia. In his first publications, we find an article entitled Cryptomnesia (^{Jung, 1905/2011b}) in which he describes the concept as a set of unconscious autonomous psychic processes in which lost memory traces reappear in consciousness in larger fragments, with photographic fidelity. This way of remembering differs from direct remembering, which uses the conscious perception of a stimulus to retrieve a memory, and indirect remembering, which consists of the unconscious perception of a stimulus and the spontaneous retrieval of the memory. In direct recall, there is conscious mediation, and in indirect recall, there is recognition of the memory as a previous event. Cryptomnesia, on the other hand, means a memory that is not recognized as a forgotten memory and is seen by the subject as an original idea (^{Jung, 1905/2011b}). Jung cites Flournoy’s research into cryptomnesia as an important source for his studies, mentioning Catherine-Elise Smith’s case of glossolalia as a characteristic cryptomnesic phenomenon. In this case, an entire autonomous linguistic system was involved. He also cites the case in which the philosopher Nietzsche describes in his Zarathustra the scene of a volcano as the gateway to hell, very similar to a scene in Julius Kerner’s book Blatter aus Prevorst [Prevorst Leaves], which he read as a child (^{Jung, 1905/2011b}). A few years later, Jung published in two parts—1911 and 1912—the book Transformations and Symbols of the Libido: Contributions to the Development of Thought¹⁶, in which he analyzed the case of Frank Miller. What for Flournoy was an example of cryptomnesia, for Jung began to illuminate his reflections on the unconscious, leading him to introduce the concept of archetype.

Another interesting case was that of an inmate at the Burghözli Hospital, who reported seeing an erect penis in the sun, and that when he shook his head to the left and right, he also saw the penis oscillating between directions, thus giving rise to the wind of the world. Jung later found a description of an almost identical vision in a manuscript of the Mitra liturgy¹⁷ . From this and other similar cases, Jung proposed the hypothesis of the existence of a functional predisposition to produce similar images that deal with repeated themes. He called this predisposition an archetype (^{Jung, 1911/1912/2011c}). Jung also clarifies in this work that the archetype is not an innate, hereditary idea, but rather a structure of the psyche predisposed to creating parallel fantasies that do not correspond to forgotten memories. This concept offers a possible explanation for the emergence of myths with similar content in different cultures that apparently never had contact with each other, such as the different symbolic readings of the sun god, so well demonstrated in Frank Miller’s second poem (^{Jung, 1911/1912/2011c}).

Jung didn’t just focus his research on the personal unconscious, as the psychoanalysis of his time did. For him, there was a broader area called the collective unconscious. According to the author:

The collective unconscious is a part of the psyche that can be distinguished from the personal unconscious by the fact that it does not owe its existence to personal experience and is therefore not a personal acquisition. While the personal unconscious is essentially made up of contents that were once conscious and yet have disappeared from consciousness because they have been forgotten or repressed, the contents of the collective unconscious have never been in consciousness and were therefore not acquired individually, but owe their existence solely to heredity¹⁸ (^{Jung, 1936/2011d, p. 51, § 88}).

To understand Frank Miller’s case, Jung draws mythological parallels, such as Goethe’s Faust, in which the protagonist, being in hell and longing for sunlight, burns his wings in hell. In Frank Miller’s fantasy, the moth goes in search of the sun and its wings melt and it burns. He defines the concept by saying that the archetype:

[...] it indicates the existence of certain forms in the psyche, which are present at all times and in all places. Mythological research calls them “motifs” or “themes”; in primitive psychology they correspond to Levy-Brühl’s concept of collective representations and in the field of comparative religions they were defined as “categories of the imagination” by Hubert and Mauss. Adolf Bastian called them “elementary thoughts” or “primordial thoughts” much earlier. From these references it becomes clear that my representation of the archetype – literally a pre-existing form – is not exclusively a concept of mine but is also recognized in other fields of science¹⁹ (^{Jung, 1936/2011d, pp. 51-52, § 89}).

From this movement of the contents of the unconscious comes poetry, and the supposed medium symbolically says how she feels: like a moth that wants to reach the unreachable, the sun. If the moth reaches the sun, its wings melt. ^{Jung (1911/1912/2011c)}, analyzing this case, confirms that this movement in search of the light is not just a literary expression or cryptomnesia, but an archetypal one, repeated in various myths.

With this study by the Swiss psychiatrist, what would previously have been just forgotten content in the personal unconscious, according to Flournoy’s concept of cryptomnesia, becomes part of a more comprehensive instance, which Jung calls the collective unconscious. It is in this instance, he speculates, that archetypes act (^{Jung, 1936/2011d}).

In this sense, there is greater harmony in the relationship between Flournoy and Jung. The presentation of the concept of cryptomnesia contributes to Jung’s reflections. However, Jung does not follow his colleague’s reasoning. He diverges (^{Jung, 1911/1912/2011c}) and develops his innovative reflection on the unconscious. The relationship with Flournoy and his work seems to have served as important material for Jung to advance his theory and lay the foundations for the concept of archetype in analytical psychology.

Final considerations

The emerging scientific psychology focused on the mediumistic manifestations that occupied the salons and social activities of the time (^{Viana, 2002}). Mediumship instigated both Flournoy and Jung. ^{Flournoy (1900)} investigated the materials produced by self-declared medium Catherine-Elise Smith (Hélène Smith), who claimed to have lived three existences in other lives, one as a Hindu princess, one as Marie Antoinette and another as an inhabitant of the planet Mars. Flournoy recognized the experience as a case of lost memory traces returning as original ideas, in other words, a case of cryptomnesia. The publication of his investigations in the book From India to the Planet Mars (1900) upset the mediumistic community of the time and led the dissatisfied medium Frank Miller to send his productions in an attempt to refute him.

^{Jung (1902/2011a)} began his psychological investigations into mediumship, which were the basis of his thesis as a doctor, with his cousin Hélene Preiswerk, who also claimed to be a medium. Later, in contact with Flournoy’s investigations, he had access to the case of Frank Miller, on which he focused in his work Symbols of Transformation (^{Jung, 1911/1912/2011c}), and in which he developed his theory of general psychic energy, at odds with the Freudian conception of libido.

The Flournoy-Jung relationship was not widely debated academically. It remained on the sidelines, with other figures from the medical and psychological world taking center stage. However, Flournoy’s influence on Jung’s work was central and contributed to the maturing of the concept of the unconscious and a detachment from the Freudian position. This concept is not born with these authors, but there is a rich deepening of the theme (^{Martinez et al., 2021}).

From the observation of mediums, ^{Flournoy (1900)} coined the concept of cryptomnesia. ^{Jung (1911/1912/2011c)}, in turn, came up with the concept of archetype and conceived the idea of an unconscious that would not be limited to the personal level, but would be part of the very history of humanity, called the collective unconscious.

Although brief, the relationship between Flournoy and Jung led to advances in psychology and the creation and development of important concepts in Jung’s work, which are still studied today and which broaden our understanding of the psyche. ■