What Was the Enlightenment?
This painting, by John Trumbull, depicts the moment on June 28, 1776, when the first draft of the Declaration of Independence was presented to the Second Continental Congress. The document incorporated many Enlightenment ideas.
Credit: Architect of the Capitol

The Enlightenment, also known as the Age of Reason, was a philosophical movement that took place primarily in Europe and, later, in North America, during the late 17thand early 18thcentury. Its participants thought they were illuminating human intellect and culture after the "dark" Middle Ages. Characteristics of the Enlightenment include the rise of concepts such as reason, liberty and the scientific method. Enlightenment philosophy was skeptical of religion — especially the powerful Catholic Church — monarchies and hereditary aristocracy. Enlightenment philosophy was influential in ushering in the French and American revolutions and constitutions. 

Historians disagree on precisely when the Enlightenment began, though most agree that the Enlightenment's origins are tied to the Scientific Revolution in the 1600s, according to the Stanford Encyclopedia of Philosophy. The Enlightenment culminated in the French Revolution (1789-1799) and was followed by the Romantic period.  

Major figures of the Enlightenment include Voltaire, John Locke, Thomas Hobbes, David Hume, Jean-Jacques Rousseau, Adam Smith, Immanuel Kant, Isaac Newton and Thomas Jefferson. 

"The origins of the philosophical ideas that would lead to the Enlightenment began during the Thirty Years War (1618-1648)," said Susan Abernethy, a Colorado-based historian and writer. "This was a long and bloody conflict fought mostly over religion and caused a great deal of social disruption. Men started to question and criticize the concepts of nationalism and warfare." 

The Age of Exploration, in which Columbus "discovered" the New World, "exposed men to other philosophies and cultures," said Abernethy. "And finally, after centuries of exploitation and abuse by monarchies and the church, regular citizens of Europe were exasperated and began to write and speak up."

"In addition, the ideas of the Renaissance led men to examine the tangible world more closely, which led to greater scientific study," Abernethy said. This movement is known as the Scientific Revolution. 

The Scientific Revolution began with the publication of Nicolaus Copernicus' heliocentric (sun-centered) universe theory in 1543. The many discoveries of the Scientific Revolution include Johann Kepler's three laws of planetary motion, Galileo Galilei's theories of motion and inertia and Tycho Brahe's new view of the stars and how they work, according to the history department at Indiana University Northwest. The Scientific Revolution ended with Isaac Newton's discovery of the law of gravitation and understanding of a mechanical universe in the late 1600s.

With each new scientific discovery, the accepted Judeo-Christian understanding of the universe changed. Gradually, thinkers embraced the Copernican-Newtonian paradigm. This paradigm holds that while the God created the universe, science defined it, and it is through science that humans can understand it, according to Indiana University Northwest. Intellectuals began to see the universe as possibly infinite and full of motion. This paradigm set the stage for Enlightenment philosophy and the embrace of mankind's rational thoughts. 

"During the Enlightenment, there was more emphasis on scientific methods, secularization of learning, religious tolerance, universal education, individual liberty, reason, progress and the separation of church and state," said Abernethy. Some key Enlightenment concepts are:

Reason: Enlightenment philosophers believed that rational thought could lead to human improvement and was the most legitimate mode of thinking. They saw the ability to reason as the most significant and valuable human capacity, according to PBS. Reason could help humans break free from ignorance and irrationality, and learning to think reasonably could teach humans to act reasonably, as well. Enlightenment philosophers saw reason as having an equalizing effect on humanity, because everyone's thoughts and behavior would be guided by reason. 

Enlightenment intellectuals thought that all human endeavors should aim to increase knowledge and reason, rather than elicit emotional responses. They advocated for universal education and secularized learning, said Abernethy.

Skepticism:Rather than being content with blind faith, Enlightenment thinkers wanted proof that something was true. They tested popular notions with scientifically controlled experiments and personal experience, though skepticism of one's own senses was another factor in Enlightenment thought, and caused complicated philosophical conundrums, according to the Stanford Encyclopedia of Philosophy. 

Enlightenment intellectuals were skeptical of the divine right of kings and monarchies in general, scientific claims about the natural world, the nature of reality and religious doctrine. "Theologians sought to reform their faith during the Enlightenment while maintaining a true faith in God," said Abernethy. The deist movement became popular during the Enlightenment. Deism holds that God exists but does not intervene on Earth. The universe proceeds according to natural, scientifically based laws. Several of America's Founding Fathers were deists, including Thomas Jefferson. 

Religious tolerance:Though skeptical of religious institutions, many Enlightenment thinkers believed that people should be free to worship as they wished. "The intellectuals of the Enlightenment vigorously sought to restrict the political power of organized religion in an effort to curtail the outbreak of intolerant religious wars," said Abernethy. 

Liberty:The Enlightenment tolerance of religion is related to the movement's emphasis on personal liberty. This concept holds that God and/or nature gave all humans basic rights and humans should be free to act without oppressive restriction. "These philosophers emphasized that government had no authority over an individual's conscience," Abernethy explained. "Individuals had rights, all men were equal and legitimate political power is based on the consent of the people and is obligated to be representative of the people's will."

Progress:The centuries before the Enlightenment were characterized by rapid changes, from the discoveries of the Scientific Revolution to the exploration of the world and the advancement in art technique during the Renaissance. Largely because of this, Enlightenment thinkers believed that the human condition was improving over time. Philosophers like David Hume and Adam Smith, both Scotsmen, tied Enlightenment ideals to politics, economic policies and more, according to the Stanford Encyclopedia of Philosophy.

Empiricism vs. rationalism:Empiricism is associated with British Enlightenment philosophers, including John Locke, George Berkeley and Hume. Empiricists argued that all human knowledge comes through the senses and sensory experiences. Rationalists, who lived primarily in continental Europe, argued that senses were untrustworthy and knowledge came from the mind, through conceiving of or intuiting ideas, according to Loyola University New Orleans.  

Toward the end of the period, philosophers began to consider exactly what they meant by the term "enlightenment." German philosopher Immanuel Kant offered this definition in his essay "What Is Enlightenment?": 

Enlightenment is man's emergence from his self-imposed nonage [many interpret nonage as "immaturity"]. Nonage is the inability to use one's own understanding without another's guidance … Dare to know! Have the courage to use your own understanding," is therefore the motto of the enlightenment.

Abernethy discussed the following men who made significant contributions to the Enlightenment:

John Comenius (1592-1670) was a Czech intellectual who espoused universal education and practical instruction. He was instrumental in introducing pictorial textbooks written in the vernacular of the student rather than Latin. He advocated for lifelong learning and the development of logical thinking as opposed to memorization by rote. He wanted education to be given to women and impoverished children.  

The Dutchman Hugo Grotius (1583-1645) was a prodigious intellectual who laid the foundation for international law based on the concept of natural law. He was one of the pioneers in putting forth the idea of a society of states governed not by force and warfare but by laws and mutual agreement to enforce those laws. He also espoused the idea of religious tolerance.

Englishmen who were influential in the Enlightenment include Thomas Hobbes (1588-1679) and John Locke (1632-1704). Hobbes championed absolutism for the sovereign but he believed in the right of the individual and the equality of all men. He stated that political communities should be based on a "social contract" meaning individuals consent either explicitly or tacitly to surrender some of their freedoms and submit to the authority of the ruler (or to the decision of the majority) in exchange for the protection of their remaining rights. Locke promoted the opposite type of government, which was a representative government.

The French Philosophes (philosophers) took the Enlightenment to new heights. Charles-Louis de Secondat, better known as the Baron de Montesquieu (1689-1755), developed the work of John Locke and espoused the concept of the separation of power by creating divisions in government. François-Marie Arouet (1694-1778), better known asVoltaire, was a prolific writer who used satire and criticism to incite social and political change. He wrote attacks on the Catholic Church and exposed injustices. He promoted the concepts of freedom of religion, freedom of expression and the separation of church and state. His writings were popular and reached many readers. Jean-Jacques Rousseau(1712-1778) wrote the book "The Social Contract," in which he championed for a form of government based on small, direct democracy, which openly signifies the will of the population.

Denis Diderot (1713-1784) was not as interested in inciting revolution but wanted to collect and disseminate Enlightenment knowledge. He embarked on a mammoth project to create the "Encyclopaedia, or a Systemic Dictionary of the Sciences, Arts, and Crafts." Many writers contributed to the 35-volume work, which as edited by Diderot and Jean le Rond d'Alembert. The "Encyclopaedia" would incorporate all of the world's knowledge and spread it to other countries all over the world.

David Hume (1711-1776) was a Scottish philosopher who gained fame as an essayist, according to the Stanford Encyclopedia of Philosophy. He was a highly influential empiricist who argued that humans were a bundle of sensations with no true selves (this is called the Bundle Theory) and that ethics were based on emotion rather than moral principles.

Immanuel Kant (1724-1804) was a German philosopher central to the Enlightenment. He synthesized rationalism and empiricism through his theories about human autonomy and set the stage for later philosophical movements, according to the Stanford Encyclopedia of Philosophy.

Adam Smith (1723-1790), a close friend of Hume, was a Scottish philosopher and economist most famous for his theory of the "invisible hand of the market," according to the Stanford Encyclopedia of Philosophy. His book "The Wealth of Nations" laid the foundation for free market economics. 

Isaac Newton (1642-1727)was an English mathematician and physicist who laid the foundation for classical mechanics and calculus. Newton developed the laws of motion and universal gravitation, which led to improvements in understanding the Copernican heliocentric universe, according to the Isaac Newton Institute for Mathematical Sciences.

Thomas Jefferson (1743-1826),an American Founding Father, was heavily influenced by Enlightenment philosophy and spent several years in France. He wrote the Declaration of Independence, which stressed Enlightenment ideas such as liberty, fundamental human rights and equality (though not for slaves), according to the Thomas Jefferson Foundation

The Enlightenment and the Scientific Revolution "saw a vast expansion in our knowledge about the world, and in the accuracy of this knowledge," said UK-based historian and writer Robert Wilde. "Part of this was down to the development of what we would consider modern scientific method," Though others had posited variations on the scientific method, Newton laid the groundwork for method we know today, according to the Stanford Encyclopedia of Philosophy

Thanks to increased literacy and the falling cost of books, the means of spreading results of science experiments improved, as did the willingness of thinkers and scientists to discuss them and adopt them, Wilde told Live Science. "I do want to mention the proto-scientists such as Gregory of Tours and other who came before: people had never stopped trying to understand the world, it was just that the successful development of modern science occurred now," he said.

"It cannot be stressed enough how instrumental the Enlightenment ideas were in changing history and society around the globe," said Abernethy. We still hold many Enlightenment ideals dear. Some of the scientific theories have evolved, but many remain as their Enlightenment authors wrote them. The concepts of liberty, reason and equality influenced early feminist Mary Wollstonecraft [mother of Mary Shelley, author of "Frankenstein"], American abolitionist Frederick Douglass and other seminal leaders.

"The ideas of religious tolerance and the separation of church and state did indeed lead to a reduction in wars due to religious differences," said Abernethy. As the power of the church waned, societies like the Freemasons and the Illuminati gained traction. Literary salons and coffeehouses emerged as new places to socialize and discuss ideas. Education for children became more widespread, and more universities were founded. Literacy rates increased dramatically, and public libraries and museums were introduced. 

"The concepts of the Enlightenment led to many revolutions, which had a tremendous effect on changing history and society," said Abernethy. "In 1688, English Protestants were instrumental in overthrowing the Catholic monarch James II and installing the Protestant monarchs William and Mary. Afterwards, the English Parliament ratified a new Bill of Rights granting more personal freedoms for Englishmen."

The most famous Enlightenment-influenced revolutions were the French and American. 

"The Founding Fathers adopted many of the ideas of the Enlightenment philosophers in writing the Constitution and the Bill of Rights," said Abernethy. They gave less power to the government and more power to the people. She added that they also established universal education in America. 

[Related: What Is Democracy? and What Is Freedom?]

The French Revolution took the English coup a step further and eliminated monarchy altogether. King Louis XVI and his queen, Marie Antoinette, were beheaded and a Republican form of government was established.

"There's a debate about whether the Enlightenment affected society, or whether a society changing through different means affected the Enlightenment," said Wilde. "Either way, the ideas of Enlightenment … influenced a French middle class to want a voice in government. In 1789, [this desire] produced a Third Estate, which broke away from royal rule, and triggered the French Revolution."

Though Enlightenment philosophy emphasized seemingly positive ideals like liberty and tolerance, Wilde noted that it could be taken to extremes. "It's important to stress that the Enlightenment thinkers weren't exactly sticking to the ideals of others … and the extremes of Enlightenment thought, such as a rejection of the church, have been blamed for the terror in the revolution." The brutality of the revolution and the subsequent Napoleonic Wars demonstrate the limits of attempting to remake society along purely rational lines. 

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