For Christians, the soul is an integral part of who you are. You have a body and you have a soul and the two are connected. Even if they don’t believe in the resurrection of the body, most Christians, in fact most Americans, believe in the immortality of the soul.
Even if you’re not religious you probably refer to the soul as a sort of fluffy spiritual term for your personality or even just a euphemism for “a life”: maybe you’ve bought Chicken Soup for the Soul or offered to sell your soul to Satan. Souls are a part of pop culture as well as religious belief. But, leaving aside religion, what is a soul, exactly? Is it some kind of immaterial ghostly stuff that is only accidentally attached to the body? Or is it more substantial? And if it is, of what is it made? And where is it in your body?
Christianity did not invent the concept of the soul, but, like many other things, it inherited it from Greek philosophy. For Plato the soul was the better half of the two parts of the human person. There was there body, which was cumbersome, temporary, and decaying; and then there was the soul (psyche), the invisible seat of wisdom, which was immortal and effectively trapped by the body until death.
In his dialogue Phaedo (also known by the title “On the Soul”), Plato recounts the final days of Socrates, who explains that not only will his soul live on after it is released from the body, but will also be all the better for it. Without the chains of emotions and senses, he says, his soul will get closer to true, pure knowledge of the natural world. Plato was the first to describe the soul as an intangible, incorporeal essence.
The majority of ancient philosophers argued that the soul was made up of physical elements. The Presocratics believed that the soul was invisible but made up of tiny particles of air (which still counted as matter). The philosopher Democritus asserted that the soul was composed of the same tiny atoms that made up fire. Heat came to be associated with the soul because it was thought to be the element that sparked life.
Epicurus, founder of the famous Epicurean school of philosophy, also believed that the soul was made from bits of air and fire, but that it also contained some special, unidentified material that was responsible for sense perception. The Stoics believed the soul was made up of many parts (including air and fire), but that rather than controlling senses, it was the seat of rationality and mentality.
For those who thought that the soul was material, this led to another question: where is it located in your body? Ancient philosophers and philosophically educated doctors like Aristotle and Galen wanted to know. For many, the soul resided in one of the mysterious and generally misunderstood internal organs. The stomach in general and the kidneys and liver, in particular, were commonly believed to be the fleshy containers of the soul. But while ancient physicians and philosophers sometimes caught a glimpse inside the body when it was wounded in battle or by accident, human dissection was largely forbidden.
The two prime candidates for the location of the soul, however, were the heart and the head. Galen thought that the life and proper thinking of the body was sustained by pneuma, which flowed throughout the body, holding it in tension. The rational soul, on the other hand, he thought was something more akin to your disposition or rational faculties. It was affected by the humors, was resident in your brain, and was thoroughly mortal.
The notion of a force spread throughout the body became influential on Christian leaders. Nemesius, a fourth century Bishop of Emesa in Syria, thought that the incorporeal soul was spread throughout the body while particular faculties were resident in the brain.
As Jessica Wright, a researcher in the Society of Fellows at USC, emphasized in her dissertation, Nemesius argued that the brain (or at least the hollow spaces or ventricles in it) was an instrument of the soul. You might not expect it, but Nemesius’ theologically grounded account of the brain’s functioning has been, as Wright puts it, “foundational in the dominant theories of brain function that developed within Arab-Islamic and European medicine.”
In articulating his theory, Galen was disagreeing with Aristotle, who thought that the heart was the seat of the soul and the brain moderated the humors. Even as Galen was profoundly influential on later medicine, the revival of interest in Aristotle in the twelfth century meant that medieval thinkers generally accepted Aristotle’s arguments about the heart. Even Parcelsus (1493-1541), who criticized Aristotle, thought that the soul took up residence in the heart. The metaphor that the head is really a reference to the dueling legacies of Aristotle and Galen (even though Galen would have admitted that the heart and brain were related).
The very same questions arose during the Enlightenment in Europe. Changing social norms, the rise of medical education, and an emphasis on observation and experimentation allowed doctors to perform anatomical studies on human cadavers. Executed criminals provided anatomists such as Andreas Vesalius (in the 16th century) and William Harvey (in the 17th) the anatomical proof used to overturn Galen.
Questions about the soul now became rooted in finding material evidence. Despite having no overriding religious agenda, those who argued for the presence of a material soul were labeled atheists, since it was presumed that this meant that human bodies operated like clocks, with all the material pieces merely doing their jobs, unimpeded by a higher power. The possibility of a material soul was even more worrying to Christians, who were concerned that a material soul might get trapped or destroyed.
The use of human bodies in medical experimentation also raised questions about the integrity of its parts, particularly when it came to debates on resurrection. Laws were enacted to ensure that all bodies received a Christian burial once they had served their purpose, but people still worried about the afterlife of those who had been cut open and dissected. What if pieces of them were missing?
Exploration of the New World and the racist caricatures of the “Natives” as cannibals that resulted, led to more extreme questions: what would happen to bodies and souls if they were torn apart and eaten? If the soul is made of matter and that matter is ingested and processed into nourishment by an animal (or a cannibal), would the soul still be intact? But whereas in Harry Potter, the division of the soul into Horcruxes renders it near impossible to destroy, Enlightenment Christians worried that they would be lost forever.
The truth was that cannibalism wasn’t really a threat to Europeans, but scientific investigation into questions of human anatomy posed a huge danger to criminal bodies. Dissections often took place in public and authorities would threaten people that crimes would be punishable by dissection.
As Raphael Hulkower has written, the 1752 Murder Act that was passed in England made dissection part of the sentence of capital punishment. In the United States a 1790 law – the only federal law relating to cadavers to be passed -- made it legal for a judge to “add dissection to a death sentence for murder” and a piece of 1784 Massachusetts legislation devised to outlaw dueling threatened deceased duelists with dissection. For people in general dissection was worse than death. As Hulkower puts it, “While execution was a threat to one’s life, dissection was an assault on one’s soul.”
The theatrical medicine of the nineteenth century brought still more questions about the integrity of the soul. Using electricity, Giovanni Aldini and Luigi Galvani began performing live ‘resurrections’ in city squares. As the bodies and faces of the frogs and cows used in the experiments twitched in lifelike fashion, onlookers wondered if the soul was even necessary for life. Could a human be just a bunch of matter animated by electricity? It was a good enough question to inspire Frankenstein, Mary Shelley’s dramatic warning about the consequences of science attempting to triumph over nature.
Anxieties about the anthropological limitations of the soul are not limited to the Enlightenment period. During World War I, as doctors began to identify the soul with both the brain and the nervous system, people became increasingly concerned about the use of chemical weapons. The Hague Declaration (1899) and the Hague Convention (1907) had forbidden the use of “poison or poisoned weapons” because the physical effects of substances like mustard on the body were horrifying to behold. But it was not only the impact on the body that worried people. It was the idea that nerve gases were an attack on the soul and the essence of a person.
To this day some scientists continue to talk about the nervous system as the home of the soul. In 2012, Professor Stuart Hameroff and British physicist Sir Roger Penrose put forward the theory that near-death experiences are the result of the soul leaving the nervous system. They further hypothesized, in a way that would please the ancient Stoics, that when a person dies their soul does not die but dissipates into the universe at large. As might be expected, this theory drew some criticism, but it remains an interesting example of the way people continue to identify the soul with the nervous system.
But even though scientists are committed to the idea that you-are-your-brain, the heart continues to have a significant hold on popularly held beliefs about who we are. In the arena of organ donation, for example, heart recipients often experience depression and existential angst after they receive the transplant. This is in contrast to kidney, liver, pancreas, and lung transplantees who might experience a sense of guilt, but rarely worry about whether they are themselves anymore. Part of the reason for this is that, as a society, we associate the heart with our emotions and identity. For heart transplant recipients it’s hard to get away from the cultural baggage associated with the heart and the sense that something of ourselves is lost when we literally lose our own.
What’s most surprising about the search for the soul, is that we keep asking the same questions. We continue to wonder and worry about what makes us who we are and which parts of our body contribute to that sense of the soul, or me-ness. Today, we spend billions of dollars on research to help explain how the human brain works in a quest to understand what makes us human. On the assumption that our brains and neural pathways make us who we are, Silicon Valley is trying to download consciousness into computers to achieve a sort of virtual immortality. But neither quantum physicists nor cognitive psychologists have definitively answered questions about the existence, composition, location, or even the necessity of the human soul.