From The Cave and the Light: Plato Versus Aristotle, and the Struggle for the Soul of Western Civilization, by Arthur Herman, pp 364-368.

The Enlightenment understood the enormous historical and cultural distance that separated it from the “ancients”— thanks in part to the rise of Christianity. The big loser in all this, however, was not Aristotle but Plato. His Republic— later so much admired by the Romantics— was the one work of political philosophy the Enlightenment most despised. Adam Smith’s teacher Francis Hutcheson pronounced its theory of politics unworkable; Smith’s friend David Hume referred to the book’s “illusory and visionary rantings.” On the other side of the Atlantic, John Adams said there were only two things he ever learned from reading Plato, and one of them was that sneezing will cure hiccups. 4

Thomas Jefferson was even more excoriating. He once confessed in a letter to Adams that he had been rereading the Republic. “I laid it down often to ask myself how it could have been that the world should have so long consented to give reputation to such nonsense as this?” Jefferson had to conclude that Plato had always been a fraud, “a dealer in mysticisms incomprehensible to the human mind,” which had been allowed to inject “an impenetrable darkness” into Western culture. “O Plato!” Voltaire exclaimed. “You have done more harm than you know.” 5

Why did the Enlightenment dislike Plato so much? Because his worldview directly contradicted the view of reality and human nature the Enlightenment derived from John Locke, and ultimately from Aristotle.‡

That view was, first, that man is an individual, an individual born with a natural sociability (an updated version of Aristotle’s zoon politikon) but also a desire to protect his own natural rights and his own self-interest. “It is love of self,” Voltaire would write, “that encourages love of others.” That self-interest was derived from nature, “which warns us to respect [the self-interest] of others.” 6 This was one reason the Enlightenment, like Aristotle, so strongly opposed the Republic’s formula for communism. The abolition of private property was not only contrary to natural right, it would also ensure that the bonds that connected men to each other would be founded not on mutual respect and friendship, but on envy or even hate. “Nothing can be conceived more destructive of human happiness, more infallibly contrived to transform men and women into Brutes, Yahoos, or Daemons,” John Adams wrote, than community of property. 7

Second, the key to happiness is understanding how the real world works. This idea stood in contrast to Plato-inspired utopian dreams, including John Calvin’s Geneva (a favorite target in the Enlightenment). Our highest ideals are not reflections of some transcendent reality, Enlightenment thinkers argued, or some higher truth. They are just that, ideals: insubstantial playthings of the mind that can deceive as often as they can inspire. This is what led Jefferson to dismiss the “dreams of Plato” and dub Plato’s ideal of a Philosopher Ruler “whimsical” and “puerile.”

Third, the only way to understand that world is through observation and analysis of our experience, not inward self-reflection. In the words of the Scottish thinker Thomas Reid, “Settled truth can be attained by observation.” Reid’s disciple John Witherspoon, who deeply influenced the American Founding Fathers, explained that we know things “by tracing facts upwards rather than reasoning downwards.” 8 Indeed, “how can we reason” at all, the poet Alexander Pope asked in his An Essay on Man, “except from what we know,” meaning from our five senses? Indeed, the formal name of Thomas Reid’s philosophy, Common Sense Realism, sums up the Aristotelian stamp on the age.

Nearly every one of these principles flowed directly from the most influential book of the age, Locke’s An Essay Concerning Human Understanding. Completed in 1686 while he was still in exile in Holland but not published until 1690, the work was a full frontal assault on the theory of knowledge stretching back to Plato, that human beings come into the world with the most valuable things they know already programmed in their minds. Mathematical truths, the rules of logic, the existence of God: All we had to do, René Descartes and other Plato-influenced thinkers had argued, was reflect deeply in order to bring them into our consciousness. 9

Locke argued that we are not born with any innate ideas or knowledge about anything. Everything we know, we have to learn from outside ourselves. The mind is (in Locke’s most famous metaphor) a tabula rasa, a blank slate on which our experiences are written by our sense perception of the world. Perception of the world, Locke wrote, is “the first step and degree towards knowledge, and the inlet of all the materials of it.” 10

What Plato had treated as the basest form of knowledge, our sensory grasp of objects, or eikasia, Locke now argued was the only path to knowledge. § What we see (or touch or hear or smell) is what we get, and the only thing we get. The rest, in a very formal sense, is up to us.

Because what we sense are either the primary qualities of objects themselves, like their size, volume, mass, velocity, length, and width; or their secondary qualities, like taste, loudness, and color. We then have to figure out how they all fit together. Our reason, Locke said, sorts the disparate sense impressions into coherent patterns on the tabula rasa, which in turn become our ideas: the one true objects of knowledge.

This was a radical step. 11 When we say, “This is a cow and this is beef stew,” or, “That’s a star, but that is a planet,” Locke insisted we are actually saying “it is my impression that this jumble of qualities must be x”— nothing more and nothing less. So how do we know that what we think and say about the world is actually true? By drawing on our past experience, Locke says, and comparing our notes with others. We say, “Did you see what I saw?” or, “Looks like a cow to me. Do you agree?” When everything fits together— our own perception and judgment and the perception and judgment of others— we can be reasonably certain that we are on the right track.

“Reasonable” is the operative word for Locke. We can never be completely certain that our idea of reality, and how things really are, exactly fit. All we know is that our perceptions lead us to think so because of their “conformity with our own experience, or the testimony of others’ experience.” 12

Someone might ask Locke how we know there really are cows and planets out there. How can we be sure we’re not just living an endless dream (or a nightmare, as in the movie The Matrix)? As a professing Christian, it would have been easy for Locke to respond: Would a beneficent Creator, infinite in power, goodness, and wisdom, leave men so confused and uncertain as to not know what’s real and what’s not? 11

Locke did not. He was content to assume that our mind’s picture of the world represents that world, because he knew that the assumption works. When I try to lift a 250-pound boulder with a fork instead of a forklift, I soon discover whether my ideas conform to reality or not. I’m free to doubt whether the cow I see is really there. When she gives me a quart of milk, however, my doubts are over— or should be.

In other words, we know we can trust our ideas when they bear practical fruit. Locke puts us firmly in the real world, just as Aristotle did. He had no patience with metaphysical speculations of the Neoplatonist kind. “You and I,” Locke once wrote to a philosopher friend, “have had enough of that fiddling.” 13

This marked an irrevocable shift in Western thinking. The old celestial spheres and hierarchies left over from the Middle Ages had already been done in by Newton’s infinite universe with its mathematical laws. As the eighteenth century wore on and Locke’s influence grew, the rest of the traditional Neoplatonist frame fell away as well. The World Soul and its divine emanations dissipated into thin air. So did the Great Chain of Being. What was left was a world of “real time” and absolute spatial dimensions. It was a world without angels or demons or ideal Forms; a world with no unseen forces except those we can measure and calculate, predict and control.

Later, some regretted this loss of belief in the supernatural. 14 Enlightenment men and women judged it a net gain. They gave up looking to angels for guidance— but they also gave up looking for witches to punish. Instead of waiting for divine radiance to transform their inner selves, they confidently relied on their reason and their five senses in order to explore their world— and to discover the laws of nature. Alexander Pope put it in verse:

Take Nature’s path, and mad Opinions leave;
All States can reach it, and all heads conceive;
Obvious her goods, in no extreme they dwell;
There needs but thinking right, and meaning well. 15

What that exploration of the world revealed to the Enlightenment (since by 1780 it included not only America and Asia but the Pacific and Australia) was a systematic natural order governing not only the physical world, but the social and political realms as well. Just as Newton had applied observation and analysis to reveal the laws of the world system, so the eighteenth century applied itself to find the laws that would allow our social and political systems to run at their optimal level. 16

No one assumed that the answers would be as precise or mathematical as Newton’s had been. The social scientist’s passion for number crunching would come later. In the end, what the Enlightenment wanted was knowledge it could work with; the knowledge it needed on Locke’s terms, in order to be happy. “What is that which moves desire?” Locke wrote. “I answer, happiness, and that alone.” 17 “The pursuit of happiness” became not just an American but the main Enlightenment enterprise for nearly one hundred years after Locke’s death.

John Locke had been a Protestant Dissenter and a Puritan at heart. His definition of happiness included a heavy dose of man’s duties to God. The eighteenth century was less particular. It found it easy to equate happiness with pleasure, although it never forgot that the latter included the pleasures of the mind. And when the Enlightenment wanted pleasure, it knew just where to look for it.

That was the city.