‘The pursuit of Happiness’ is a famous phrase in a famous document, the United States Declaration of Independence (1776). But few know that its author was inspired by an ancient Greek philosopher, Epicurus. Thomas Jefferson considered himself an Epicurean. He probably found the phrase in John Locke, who, like Thomas Hobbes, David Hume and Adam Smith, had also been influenced by Epicurus.

Nowadays, educated English-speaking urbanites might call you an epicure if you complain to a waiter about over-salted soup, and stoical if you don’t. In the popular mind, an epicure fine-tunes pleasure, consuming beautifully, while a stoic lives a life of virtue, pleasure sublimated for good. But this doesn’t do justice to Epicurus, who came closest of all the ancient philosophers to understanding the challenges of modern secular life.

Epicureanism competed with Stoicism to dominate Greek and Roman culture. Born in 341 BCE, only six years after Plato’s death, Epicurus came of age at a good time to achieve influence. He was 18 when Alexander the Great died at the tail end of classical Greece – identified through its collection of independent city-states – and the emergence of the dynastic rule that spread across the Persian Empire. Zeno, who founded Stoicism in Cyprus and later taught it in Athens, lived during the same period. Later, the Roman Stoic Seneca both critiqued Epicurus and quoted him favourably.

Today, these two great contesting philosophies of ancient times have been reduced to attitudes about comfort and pleasure – will you send back the soup or not? That very misunderstanding tells me that Epicurean ideas won, hands down, though bowdlerised, without the full logic of the philosophy. Epicureans were concerned with how people felt. The Stoics focused on a hierarchy of value. If the Stoics had won, stoical would now mean noble and an epicure would be trivial.

Epicureans did focus on seeking pleasure – but they did so much more. They talked as much about reducing pain – and even more about being rational. They were interested in intelligent living, an idea that has evolved in our day to mean knowledgeable consumption. But equating knowing what will make you happiest with knowing the best wine means Epicurus is misunderstood.

The rationality he wedded to democracy relied on science. We now know Epicurus mainly through a poem, De rerum natura, or ‘On the Nature of Things’, a 7,400 line exposition by the Roman philosopher Lucretius, who lived c250 years after Epicurus. The poem was circulated only among a small number of people of letters until it was said to be rediscovered in the 15th century, when it radically challenged Christianity.

Its principles read as astonishingly modern, down to the physics. In six books, Lucretius states that everything is made of invisible particles, space and time are infinite, nature is an endless experiment, human society began as a battle to survive, there is no afterlife, religions are cruel delusions, and the universe has no clear purpose. The world is material – with a smidgen of free will. How should we live? Rationally, by dropping illusion. False ideas largely make us unhappy. If we minimise the pain they cause, we maximise our pleasure.

Secular moderns are so Epicurean that we might not hear this thunderclap. He didn’t stress perfectionism or fine discriminations in pleasure – sending back the soup. He understood what the Buddhists call samsara, the suffering of endless craving. Pleasures are poisoned when we require that they do not end. So, for example, it is natural to enjoy sex, but sex will make you unhappy if you hope to possess your lover for all time.

Epicurus also seems uncannily modern in his attitude to parenting. Children are likely to bring at least as much pain as pleasure, he noted, so you might want to skip it. Modern couples who choose to be ‘child-free’ fit within the largely Epicurean culture we have today. Does it make sense to tell people to pursue their happiness and then expect them to take on decades of responsibility for other humans? Well, maybe, if you seek meaning. Our idea of meaning is something like the virtue embraced by the Stoics, who claimed it would bring you happiness.

Both the Stoics and the Epicureans understood that some good things are better than others. Thus you necessarily run into choices, and the need to forgo one good to protect or gain another. When you make those choices wisely, you’ll be happier. But the Stoics think you’ll be acting in line with a grand plan by a just grand designer, and the Epicureans don’t.

As secular moderns, we pursue short-term happiness and achieve deeper pleasure in work well done. We seek the esteem of peers. It all makes sense in the light of science, which has documented that happiness for most of us arises from social ties – not the perfect rose garden or a closet of haute couture. Epicurus would not only appreciate the science, but was a big fan of friendship.

The Stoics and Epicureans diverge when it comes to politics. Epicurus thought politics brought only frustration. The Stoics believed that you should engage in politics as virtuously as you can. Here in the US where I live, half the country refrains from voting in non-presidential years, which seems Epicurean at heart.

Yet Epicurus was a democrat. In a garden on the outskirts of Athens, he set up a school scandalously open to women and slaves – a practice that his contemporaries saw as proof of his depravity. When Jefferson advocated education for American slaves, he might have had Epicurus in mind.

I imagine Epicurus would see far more consumption than necessary in my own American life and too little self-discipline. Above all, he wanted us to take responsibility for our choices. Here he is in his Letter to Menoeceus:

For it is not drinking bouts and continuous partying and enjoying boys and women, or consuming fish and the other dainties of an extravagant table, which produce the pleasant life, but sober calculation which searches out the reasons for every choice and avoidance and drives out the opinions which are the source of the greatest turmoil for men’s souls.

Do you see the ‘pursuit of happiness’ as a tough research project and kick yourself when you’re glum? You’re Epicurean. We think of the Stoics as tougher, but they provided the comfort of faith. Accept your fate, they said. Epicurus said: It’s a mess. Be smarter than the rest of them. How modern can you get?