Secular inquiry is fragile. The history of trying to understand the world without reference to the gods is remarkably tumultuous – so much so that it is baffling that secular inquiry, as a social phenomenon, should have survived at all. Many thinkers throughout history have devoted themselves to keeping nonreligious thought alive, but six thinkers in particular stand out as the pillars upon which the thread of secular inquiry hangs. This is the story of those individuals and their colossal intellectual legacy.
The story begins with Thales of Miletus, a Greek man who lived twenty-six centuries ago on the western shores of what is now Turkey. It is with Thales that the very idea of secular inquiry was born. Before Thales, the Greeks thought that all natural phenomena could be explained by the actions of the gods: the passions of the sea were the whims of Poseidon, autumn turned to winter when Persephone descended into the underworld, and lightning was cast by Zeus in fits of fury.
But Thales saw things differently. Thales thought that such phenomena could be explained by natural causes. Not much is known about what he actually believed, since most of his writings have been lost to the depths of history. But his simple idea that we could reason about how things come to be without appealing to the gods changed the Ancient Greek world. And it is because of this that the Greeks called Thales the first philosopher. And it is also for this reason that we now call him the first scientist.
Thales’ efforts to understand the world around him led many Greeks to abandon mythology in their attempts to explain nature. There were many ideas put forth by the ancients. But one idea, which is particularly astonishing in its prescience, was championed by the second thinker on our list, Democritus. Like all other Greek thinkers, Democritus was heir to the intellectual enterprise begun by Thales.
Democritus proposed that everything is made up of tiny bits of matter invisible to the human eye. Democritus’ thinking was this: everything can be divided into smaller parts, things can decay or change shape, and we can mix things together. Therefore, he concluded, the objects around us are likely made up of smaller objects. He called these smaller objects “atoms.”
There was substantial disagreement with Democritus’ atomic theory in the ancient world, but it was this very idea that would come to form the backbone of one of the most radical philosophies of Ancient Greece: the school of thought introduced by the third thinker on our list, the Athenian philosopher Epicurus.
Like Democritus, Epicurus was an atomist, asserting that all there was in our world were atoms moving through the void. Even the gods, he thought, were made of atoms. But from the doctrine of atomism Epicurus also drew lessons about how to live a good and ethical life. Because he did not think that right or wrong were based on the rule of the gods, he thought that we should instead seek to minimize suffering and maximize pleasure. That is not to say that we should be hedonists. Instead, Epicurus taught, we should simply try to maintain a state of serenity, enjoy the company of friends and loved ones, and be kind.
Epicurus’ teachings grew in popularity and remained a dominant force in philosophy well into the rise of the Roman Empire. And it is in Rome, almost two centuries after Epicurus’ death, that we see the most stunning expression of Epicurean science and philosophy in a five-book poem called De Rerum Natura, or On The Nature of Things. Composed by the philosopher and poet Titus Lucretius Carus – the fourth thinker on our list – the poem is an exploration of the nature of the world and the nature of the mind. Lucretius’ goal was explicit. It was to free his readers from the fetters of superstitious thinking, to show them that we can try to understand the world without reference to the gods. The poem seems radical even now, for in it Lucretius disavows the influence of the heavens, rejects the existence of an immortal soul, and even proposes a rudimentary theory of evolution by natural selection.
After the collapse of the Roman Empire, De Rerum Natura was forgotten for millennia. And with it died the Classical attempt to explain the world without reference to the gods, at least in Europe. But a chance event in a remote German monastery almost two thousand years later reversed the tides of history. It is there that an Italian scholar named Poggio Bracciolini – the fifth thinker on our list – happened upon what was likely the last surviving copy of De Rerum Natura. Recognizing that the poem was a window into the Classical past, Poggio copied the manuscript by hand and sent it to a friend, who made another copy and sent it to yet another friend, who himself made a copy, and so on.
When De Rerum Natura began to circulate again in the early Renaissance, it was seen as heretical. To Christian Europe, the suggestion that there is no immortal soul, that the gods do not care about human affairs, or that all that exists are atoms in the void was at best nonsensical and at worst threatening. Yet despite its profanity, the poem continued to proliferate amongst educated Europeans who read it because of its beautiful poetry – and its poetry is indeed stunning. In the margins of the poem they would note the meter of Lucretius’ verse or reflect on the philology of his Latin. Later editions of the poem were even prefaced with warnings not to take the ideas of the work seriously, that it was only worth reading because of the sublimity of its verse. It took another two centuries before one man would directly confront the sacrilegious ideas of the ancient world. That man was the sixth and final thinker on our list, French essayist Michel de Montaigne, whose own writings would go on to profoundly influence the Enlightenment and the birth of the modern era. In his copy of De Rerum Natura we see one annotation scribbled over and over: “Contre la religion.”
Through its influence on thinkers as diverse as Montaigne and Thomas Jefferson, De Rerum Natura was a lifeline to the ancient enterprise of secular inquiry, which was begun by Thales and maintained by his intellectual descendents all the way down to Lucretius. And when we reflect on how utterly unlikely it was that De Rerum Natura should have been rediscovered, we cannot help but see the fragility of science and secular thought. And it is because of that fragility that we owe it to ourselves – and to the inheritors of our intellectual culture – to continue unabated in our exploration of the natural world and our place in it.