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20 Bizarre Beliefs Europeans Had During the Enlightenment

Shannon Quinn - June 20, 2025

The Enlightenment is often celebrated as a period when reason, science, and intellectual curiosity transformed European society. Brilliant thinkers challenged tradition and sparked revolutions in philosophy and politics. Yet, even in this so-called Age of Reason, many clung to startlingly bizarre beliefs—from mystical sciences to peculiar superstitions. This list reveals twenty of the most unusual ideas that persisted among Europeans, showing how even the brightest minds sometimes struggled to separate fact from fiction. Prepare to be surprised by the curious contradictions of this fascinating era.

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1. Spontaneous Generation

One of the most persistent Enlightenment-era beliefs was spontaneous generation—the idea that life could spring from non-living matter. Many Europeans thought maggots simply appeared from decaying meat or that mice could be born from piles of grain and rags. While some skeptics questioned this theory, it wasn’t until Louis Pasteur’s experiments in the 19th century that spontaneous generation was finally disproven. Until then, the notion fascinated and puzzled even the most rational minds.

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2. Phlogiston Theory

During the Enlightenment, many chemists subscribed to the phlogiston theory. They believed a mysterious, fire-like substance called phlogiston was released when things burned. This idea shaped scientific thought for decades, despite mounting evidence against it. It wasn’t until Antoine Lavoisier demonstrated that combustion actually involved oxygen that the theory was finally overturned. For more on this curious chapter in chemistry, see Scientific American.

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3. Animal Magnetism

In the late 18th century, Franz Mesmer introduced the world to animal magnetism. He argued that an invisible force flowed through all living things and that manipulating this energy could cure disease. Patients flocked to Mesmer for these dramatic “magnetic” treatments, even though no scientific evidence supported his claims. While animal magnetism was eventually debunked, Mesmer’s ideas laid the groundwork for modern hypnotism. Discover more about this fascinating belief at Britannica.

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4. Hollow Earth Theory

Among the more outlandish Enlightenment ideas was the hollow Earth theory. Promoted by notable figures like Edmond Halley, some believed our planet was hollow—possibly with hidden civilizations inside. This notion captured the imaginations of scientists and writers alike, despite lacking evidence. To learn more about this enduring myth, visit Smithsonian Magazine.

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5. Bloodletting as Universal Cure

During the Enlightenment, bloodletting was considered a near-universal remedy for illness. Physicians believed that removing blood helped balance the body’s four humors, thought to govern health. Despite its dangerous risks—including infection and death—bloodletting remained a cornerstone of medical practice well into the 19th century. This treatment was prescribed for everything from fevers to headaches. Explore the history of bloodletting to see how long this practice endured.

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6. Lunar Influence on Madness

Many Enlightenment-era Europeans believed the full moon could trigger madness and unusual behavior. This idea gave rise to the word “lunatic,” stemming from Luna, the Roman moon goddess. Physicians and laypeople alike connected lunar cycles to mental health, shaping both language and treatments for the mentally ill. For a deeper look at the moon’s supposed role in madness, see Psychology Today.

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7. Miasma Theory of Disease

For centuries, Europeans believed that illnesses such as the plague and cholera were spread by miasma—noxious, foul-smelling air. This theory shaped city planning and public health efforts, often with little success. Authorities burned incense, carried sweet-smelling herbs, and even designed buildings to ward off “bad air.” It wasn’t until the rise of germ theory that the concept of miasma was finally debunked. Read on for more about this persistent belief.

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8. Homunculus in Sperm

A particularly strange Enlightenment belief was the homunculus theory. Some scientists thought that each sperm contained a tiny, fully-formed human—called a homunculus—ready to grow inside the womb. This idea, known as preformationism, placed all responsibility for heredity on the father. Modern embryology eventually disproved this notion. Find more fascinating details here.

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9. Witchcraft and Superstition

Even as Enlightenment thinkers championed reason, fear of witchcraft persisted across Europe. Accusations and trials continued well into the 18th century, with communities blaming unexplained misfortunes on supposed witches. Ironically, some Enlightenment writers debunked these superstitions, while others sensationalized them for dramatic effect. The era’s struggle between old beliefs and new ideas is striking. Learn more about the lingering shadow of witchcraft.

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10. Vitalism

During the Enlightenment, many scientists embraced vitalism—the belief that living organisms were animated by a unique, non-physical “life force.” This idea suggested that life could not be fully explained by chemistry or physics alone. Vitalism slowed the acceptance of emerging biochemical discoveries, as many insisted something mysterious set life apart. You can find more on this intriguing belief here.

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11. Geocentrism’s Lingering Hold

Despite scientific breakthroughs from Copernicus and Galileo, the geocentric model—placing Earth at the universe’s center—remained popular among some Enlightenment thinkers. Tradition and religious beliefs made it difficult for many to accept the heliocentric view. This resistance shows how old worldviews can persist, even in an age of reason. See the historical context for more.

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12. The Power of Relics

Even as Enlightenment skepticism spread, the veneration of relics—bones, clothing, or objects linked to saints—remained widespread. Many believed these sacred items could heal the sick, protect against disaster, or bring good fortune. Churches displayed and guarded relics as sources of wonder and devotion. This blend of faith and superstition endured, revealing how the miraculous still captivated Enlightenment minds. See more about religious relics and their influence.

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13. Alchemy’s Endurance

Despite advances in scientific thinking, alchemy still captivated many Enlightenment-era minds. The quest to turn base metals into gold and discover the legendary philosopher’s stone mixed mystical beliefs with emerging chemical knowledge. Both scientists and nobles pursued alchemical experiments, hoping for wealth or immortality. Alchemy’s tantalizing promises lingered even as modern chemistry took shape. Explore the history of alchemy for further insight.

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14. Fear of Vampires

During the Enlightenment, vampire hysteria swept across Eastern Europe and even influenced educated Europeans. Reports of the dead returning to prey on the living led to mass panics, exhumations, and bizarre rituals. This fear gripped communities, blurring the lines between folklore and reason. Discover the real history behind these chilling beliefs here.

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15. Sympathetic Magic

Even in the Enlightenment, sympathetic magic fascinated Europeans. This belief held that objects or people could affect each other at a distance if they were somehow connected. A famous example: the idea that treating a weapon’s blade with a healing salve could cure the victim’s wound. Such magical thinking persisted alongside rational medicine. Learn more curious details about sympathetic magic here.

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16. Fear of Werewolves

Despite Enlightenment advances, werewolf legends endured in rural Europe. People feared humans could transform into wolves, and actual werewolf trials took place in some regions. These chilling beliefs reveal how folklore and superstition persisted, even as rational thought gained ground. Discover more about the fascinating history of werewolves here.

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17. Astrology’s Scientific Status

During the Enlightenment, astrology retained surprising credibility among Europe’s elite. Nobles and even leading intellectuals often consulted horoscopes for decisions about marriage, politics, and health. Astrology’s complex charts and calculations gave it an air of scientific legitimacy, blurring the line between astronomy and superstition. Its influence remained strong, despite growing skepticism. For more on astrology’s historical role, see here.

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18. The Mandrake Root’s Magical Powers

The mandrake root, known for its human-like shape, inspired countless legends across Enlightenment Europe. People believed it possessed magical powers, capable of bringing love, fertility, or even protection from harm. Mandrakes were highly prized in both folk medicine and occult rituals, despite the lack of scientific proof. Their mystique reveals how ancient traditions lingered. Read more about the mandrake’s fascinating reputation.

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19. The Healing Power of Unicorn Horns

During the Enlightenment, apothecaries sold powdered “unicorn horn”—usually narwhal tusk—as a powerful antidote against poison and disease. These rare “remedies” commanded enormous prices, as many believed in their magical healing abilities. The myth of the unicorn’s horn persisted long after science questioned its existence. Find more details about this curious trade here.

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20. The Philosopher’s Stone and Elixirs of Immortality

The quest for the philosopher’s stone captivated Enlightenment alchemists and thinkers alike. Many believed this legendary substance could transform base metals into gold and produce elixirs granting immortality or perfect health. This pursuit blurred the boundaries between scientific experimentation and fantastical myth. The allure of eternal life remained powerful, even as rational inquiry advanced. More details on this enduring obsession.

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Reflections on Enlightened Eccentricities

The Enlightenment is often hailed as a triumph of reason and progress, yet these bizarre beliefs remind us that tradition, myth, and science often coexisted in fascinating ways. Even the most celebrated thinkers were shaped by their era, blending old superstitions with bold new ideas. Intellectual progress is rarely straightforward—it’s a patchwork of breakthroughs and blind spots. As we marvel at the eccentricities of the past, let’s remember to question our own assumptions and remain open to discovery.

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