Denis Diderot on the Art of Freethinking and the Dangers of Religion

Diderot and the Art of Thinking FreelyDenis Diderot, the French philosopher, art critic, and writer, was described by Voltaire as a pantophile, or the type of person who falls in love with everything they study, from mathematics, science, and medicine to philosophy, politics, literature, and art. So while Diderot never produced a masterpiece that would put him in the highest ranks of philosophy or literature, he did over the course of his life think and write about a wider range of topics than most.

This disposition had several benefits. First, it made Diderot uniquely suited for the position of chief editor of the Encyclopedie, the first and largest project to secularize all human knowledge from the materialist and humanist perspective. More than any other work, the Encyclopedie captured the full spirit of Enlightenment thought.

Second, as is often the case, those with such wide educational interests often come to find the prevailing religious and cultural views grossly oversimplified and delusional. The idea that one group of ancient people discovered the immutable truth regarding the origins and purpose of the universe is an affront to the intelligence of anyone who is widely read in the natural and social sciences. And thus Diderot also become the most outspoken atheist and proponent of freethinking of the era, a position that landed him in jail for three months and brought on constant harassment from the authorities and the Church.

While Diderot is known mainly for his work on the Encyclopedie, along with various literary works, some of his most profound writing and ideas were published posthumously. Diderot had several reasons for not publishing these works; first and most obvious was the threat of imprisonment, but there was also a more profound reason. Diderot wrote:

“One only communicates with force from the bottom of the grave; that is where one must imagine oneself; and it is from there that one should speak to mankind.”

Diderot wrote that “posterity is to the philosopher as heaven is to the man of religion.” He knew that contemporary biases could result in both his imprisonment and in the rejection of his progressive ideas, but that posterity would be in a better position to evaluate his arguments.

In Diderot and the Art of Thinking Freely, Andrew S. Curran unearths these unpublished writings and shows what we can learn from the Enlightenment-era polymath. Curran shows how “[Diderot] dreamed of natural selection before Darwin, the Oedipus complex before Freud, and genetic manipulation two hundred years before Dolly the Sheep was engineered.” Diderot also foreshadowed Karl Marx with his writings on class struggle (Marx cited Diderot as his favorite author) and predicted the Haitian slave revolt (Diderot was a vociferous opponent of slavery).

Perhaps most interestingly, Diderot predicted the current situation that the United States finds itself in. Diderot wrote:

“People of North America: may the example of all those nations that have preceded you, and especially that of your motherland, be your guide. Beware of the abundance of gold that brings about the corruption of morals and the scorn of law; beware of an unbalanced distribution of wealth that will produce a small number of opulent citizens and a horde of citizens in poverty, a situation that will engender the insolence of some and the deprivation of others.”

As Curran writes, “The real threat to American democracy, as Diderot had also suggested in his Essay on Seneca, came less from foreign powers than from the unintended consequences of future success; luxury goods, the rise of class tensions, political corruption, venality, and, in the worst scenario, perhaps even a dictator.”

John Adams had similar warnings, as when he wrote to Jefferson, “As long as Property exists, it will accumulate in Individuals and Families…the Snow ball will grow as it rolls.” Adams also wrote elsewhere, “In every society known to man, an aristocracy has risen up in the course of time, consisting of a few rich and honorable families who have united with each other against both the people and the first magistrate.”

The Enlightenment philosophers of the era—both Diderot and the US founders—were keenly aware of the problems of inequality, wealth, and undue political influence and power. It would do us all well to remind ourselves of their concerns.

What else can Diderot teach us today? Here are five lessons that are as relevant as ever:

  1. Today we take for granted our freedoms of speech and press without realizing that these rights were strenuously fought for, often against religious and conservative authorities that had the power to censor books and lock people up. We should remember that the only way to advance knowledge is through the free expression and criticism of ideas. The second we think an individual, group, or idea is infallible is the second we’re in deep trouble.
  2. In an era of specialization, it’s just as important to read widely as it is to read deeply. Being educated means coming to understand how little you know about the wealth of knowledge that exists in the world, and the complexity and uncertainty regarding most subjects.
  3. The two virtues that are most valuable (and that are little discussed) are intellectual humility and intellectual courage. Intellectual humility, the opposite of dogmatism, is the recognition that no one holds a monopoly on the immutable truth regarding any subject, and that you should be careful when speaking outside of your area of expertise. The second virtue, intellectual courage, is the ability to criticize all ideas, even the ones most commonly accepted. Posterity always favors the contrarians.
  4. Religion is dangerous when given political power. Thomas Jefferson advocated for a “wall of separation between Church and state” because everyone (including Diderot) in the 18th century knew what kind of damage religion can do. Faith-based positions are by definition not amenable to reason, and therefore when conflicts arise the only recourse is through violence or suppression. Secular democratic governments are ideal because non-violent processes and institutions are in place for the resolution of conflict, using reason and argument instead of suppression and force.
  5. No subject should be beyond criticism. Philosophy has emancipatory value because it allows us to see where our reasoning has gone wrong, especially as new evidence becomes available. When you challenge someone’s religion, you’re not attacking them personally; you’re attacking an idea, and ideas should never be beyond criticism for fear of offending someone. Again, having intellectual courage is having the capacity to change one’s mind in the face of better explanations, and is a virtue needed now more than ever.

Further Reading

Here are some additional books on the topic of the Enlightenment, freethinking, and the open society:

The Dream of Enlightenment: The Rise of Modern Philosophy by Anthony Gottlieb

Enlightenment Now: The Case for Reason, Science, Humanism, and Progress by Steven Pinker

The Portable Enlightenment Reader

Freethinkers: A History of American Secularism by Susan Jacoby



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