Philosophy began as a way of living more deeply, of making sense of the world and ourselves. The ancient philosophers were seekers, not scholars. They asked hard questions, challenged assumptions, and shaped the modern world.
These notes are based on the Ancient Philosophy lecture series delivered by Dr. James Orr, Associate Professor of Philosophy of Religion at the University of Cambridge. The series explores six major philosophical schools from antiquity, beginning with the early natural inquiries of the Ionian and Eleatic thinkers, and moving through the transformative ideas of Plato and Aristotle, as well as the practical wisdom of Stoicism and Epicureanism. These notes explore both what the ancient philosophers believed, and also how their ideas continue to offer practical guidance for living wisely today.
The Ionian School: The Birth of Natural Inquiry
Key Idea: The world is intelligible, not magical.
Emerging in Ionia (modern-day Turkey), thinkers like Thales, Anaximander, and Anaximenes proposed that everything in the universe had a natural explanation. They replaced myth with observation, marking the shift from mythos to logos.
- Thales said everything was water.
- Anaximander proposed the apeiron (the indefinite) as the origin of all things.
- Anaximenes believed everything was air in different forms.
They weren’t trying to get it exactly right. Instead, they were trying something new: asking how the world worked using reason.
Takeaway: Begin by questioning what you take for granted. Look for patterns, not just stories.
From Mythos to Logos: A New Way of Understanding
Before the Ionian philosophers, knowledge came through mythos, poetic stories like those in Homer and Hesiod, which sought wisdom through divine inspiration. The Ionians shifted toward logos, which was a commitment to reason, observation, and argument.
This wasn’t a rejection of the divine, but a change in posture: instead of appealing to the gods for knowledge, they began asking nature to explain itself.
Takeaway: True learning begins when we stop accepting stories at face value and start asking for explanations.
Heraclitus of Ephesus: Embracing Change
Heraclitus gave us one of the most provocative ideas in philosophy: everything is in flux. You cannot step into the same river twice, he said, because the waters—and you—are always changing.
Yet beneath this ceaseless motion, he believed there was a hidden order: the logos. This wasn’t just logic; it was a cosmic principle, an underlying harmony in conflict itself.
Reflection: If change is the only constant, how do we find stability in our lives? Is there a deeper pattern beneath the chaos?
Early Sparks of Skepticism and the Divine
These early thinkers didn’t reject the divine—they redefined it. To them, the divine wasn’t a personified god on a cloud, but the underlying order of things. Anaximander’s boundless apeiron and Heraclitus’ logos were sacred in their own right.
Xenophanes took this further, challenging the anthropomorphic gods of Homer. “If horses had gods,” he quipped, “they’d look like horses.” He planted early seeds of religious critique—without discarding the idea of divinity altogether.
Why This Still Matters Today
These thinkers were were poets, mystics, wanderers, and citizens, trying to make sense of life. They believed ideas should shape how we live: what we eat, how we act, and even how we grow our beards.
Their questions—What is real? How can we know? What holds the world together?—are still our questions.
And they remind us that philosophy is not about knowing everything. It’s about not being afraid to ask.
The Eleatic School: Questioning Change Itself
Key Idea: True reality doesn’t change.
The Eleatic School was a group of thinkers from a place called Elea, in southern Italy. They didn’t believe that things like fire, water, or air made up everything. Instead, they focused on a big question: What is real, and does it ever really change?
A philosopher named Parmenides said that real things never change at all. He believed that everything that truly exists always stays the same, forever. If we think things are changing—like trees growing or people getting older—it’s because our eyes and senses are tricking us. To Parmenides, the only way to know what’s real is by thinking carefully, not by trusting what we see or hear.
This school of thought started a big idea in philosophy:
- Some things seem to change (like people, plants, and seasons), but
- Maybe there’s something deeper that never changes at all.
Big Idea:
The Eleatic school laid the groundwork for metaphysics, the branch of philosophy concerned with what really is beneath the flux of appearances.
The Eleatic School asks deep questions like:
What is real?
What stays the same underneath everything that changes?
Plato’s Perspective: The World of Forms
Fifth-century Athens was the birthplace of theatre, history, and democracy. Amid the chaos of war and the shifting tides of political power, intellectual life thrived. In particular, rhetorical skill became a commodity. Sophists—skilled speakers and paid educators—taught persuasive techniques not always rooted in truth. In response to this relativism, Plato offered something deeper.
Plato’s philosophical mission began with his mentor, Socrates, whose trial and execution deeply shaped him. Socrates stood apart from the sophists, seeking truth through relentless questioning rather than persuasion. Plato preserved this spirit in his dialogues, where Socrates interrogates assumptions to reveal ignorance and provoke reflection. Through these conversations, Plato developed a style of inquiry known as dialectic—a method of collaborative truth-seeking that remains foundational in philosophy today.
Plato’s choice to write dialogues rather than treatises reflects his belief that philosophy is a lived experience, not a list of answers. Early dialogues often end in aporia—a state of puzzlement or philosophical dead-end. These unresolved inquiries reflect a key insight: admitting what we do not know is a vital step toward deeper understanding.
The central insight of Plato’s metaphysics is that reality has two layers. There is the world of appearances—changeable, fleeting, and dependent on sense experience. Then there is the world of Forms—stable, eternal, and accessible only through reason. These Forms (such as Justice, Beauty, or the Good) are not simply abstract ideas; they are more real than the objects we see around us. Just as mathematical truths do not change, the Form of Justice remains constant, even when societies disagree about it.
Plato’s allegory of the cave (in Republic Book VII) vividly illustrates the journey from ignorance to knowledge. Prisoners watch shadows on a wall, mistaking them for reality. One escapes, sees the sun (symbolising the Good), and realises the truth. The allegory suggests that most of us live in illusion until we begin the difficult ascent of philosophical inquiry. It’s not enough to see the flickering shadows of opinion—we must turn toward what is constant and real.
Key Idea: The visible world is a shadow of a higher reality.
For Plato, reality had two layers:
- The world of Appearances, where everything changes.
- The world of Forms, where truth, justice, and beauty exist unchanging.
Takeaway: Don’t settle for surface-level thinking. Seek deeper, universal truths.
Plato admired mathematics because it offered certainty. A theorem like “2 + 2 = 4” is timeless and universal. Scientific truths, by contrast, are always provisional. This made mathematics a model for Plato’s idea of real knowledge—what he called episteme. For Plato, a just city, like a well-ordered soul, must be grounded in such stable truths, not shifting opinions. That’s why philosopher-rulers, in Plato’s utopia, are required to master geometry before they study dialectic.
Though famous for its metaphysical ideas, The Republic is ultimately about justice. Plato draws a powerful analogy between the soul and the city. In a just soul, reason governs with wisdom, spirit enforces courage, and appetite obeys with discipline. A just city mirrors this balance, with philosopher-kings ruling for the common good. True justice, for Plato, is a kind of harmony—within ourselves and our communities.
According to Plato:
- Truth requires more than opinion: Plato reminds us that clarity comes from deep reflection, not popularity.
- Knowledge is not the same as belief: Real knowledge must be rooted in stable, intelligible reality—not shifting appearances.
- Justice begins within: Before we can build just societies, we must cultivate order in our own souls.
- Learning starts with humility: Like Socrates, we must be willing to say “I don’t know” before we can truly learn.
Aristotle’s Approach: Flourishing in the Real World
When people talk about the great thinkers of the past, they often start with Plato. But his student, Aristotle, changed the world in his own quiet way. He helped create many of the things we now call science, logic, and the study of ethics. In fact, the word “ethics” comes from ta ethika, meaning matters of character. If you’ve ever asked, “What kind of person should I be?” you’re already thinking like Aristotle.
Aristotle was born in northern Greece and later had to leave Athens. While Plato liked to think about big ideas in the heavens, Aristotle looked closely at the real world around him. He helped make philosophical ideas easier to understand by bringing them down to earth.
After studying under Plato at the Academy, Aristotle went on to found his own school, the Lyceum. Whereas Plato saw knowledge as an ascent to a world of ideal forms, Aristotle believed that understanding began with what we can observe. This bottom-up approach made him the world’s first systematic thinker.
Key Idea: Fulfil your purpose through rational living.
Aristotle, Plato’s student, rejected otherworldly Forms. For him, reality is in this world—in the concrete, living things around us. He introduced:
- Four Causes: material (what it’s made of), formal (its shape), efficient (what makes it), and final (its purpose).
- Eudaimonia: the good life is about flourishing, not fleeting pleasure.
- Virtue Ethics: become good by doing good, habitually.
Aristotle believed that soul (psyche) is what animates living things. Plants have a nutritive soul. Animals add sensory faculties. But humans are unique in having a rational soul. This power of reason makes us capable of understanding the world—and of understanding ourselves.
Takeaway: To live well, we must nurture our rational nature through reflection and virtuous action.
In Nicomachean Ethics, Aristotle asks the most important question: What is the good life? His answer is eudaimonia. Poorly translated as “happiness”, eudaimonia really means flourishing or living well in accordance with our nature. It is not a fleeting mood, but a stable condition of moral and intellectual excellence.
Aristotle believed that to live a good and happy life, we need to:
- Practice good qualities like courage, fairness, and self-control.
- Try to make choices that make sense.
- Find a balance in how we act—not too much and not too little, but just right.
Even with reason, we often choose what we know is harmful. Aristotle calls this akrasia: weakness of will. Overcoming akrasia requires not just knowing the good, but training ourselves to desire it through repeated, deliberate action. We become what we habitually do.
Challenge: What habits in your life bring you closer to your own version of flourishing? Which take you further away?
Finally, Aristotle argues that the good life is not lived in isolation. Human beings are political animals (politikon zoon). We thrive in communities, beginning with the family (oikos), then villages (kome), and ultimately the city-state (polis). A well-ordered society is essential to individual flourishing.
Stoicism: Rational Strength in a Chaotic World
Stoicism offered a radical yet practical answer to a turbulent and unpredictable world. While rooted in ancient Athens, its influence has rippled through Roman thought, Enlightenment philosophy, cognitive behavioural therapy—and now, through the modern self-help movement.
Zeno of Citium was once in a shipwreck and lost everything. But instead of giving up, he found a new path, which began in a bookshop in Athens. It was there that he came to learn about Socrates and met a teacher named Crates, which started his journey into philosophy.
Zeno later started his own school in Athens, and they met in a place called the Stoa Poikile (a painted porch). That’s why his way of thinking is called Stoicism.
Stoicism teaches us to live simply, be calm, and do what’s right. It was inspired by another group called the Cynics, who believed in living with very little. But Zeno made the ideas easier to follow and more friendly to everyday life.
Key Idea: Live according to nature and reason.
Founded by Zeno of Citium, Stoicism teaches that the world is governed by logos, a rational order. We must align our lives with it.
- Focus only on what you can control.
- Let go of destructive emotions by examining your judgments.
- Accept fate without complaint, and act with virtue regardless of outcomes.
Marcus Aurelius, Seneca, and Epictetus are its greatest exponents.
Reflection: What emotions are clouding your judgment? What could change if you let reason lead?
Plato believed that true perfection lived in an invisible world of perfect ideas. But the Stoics thought something different. They believed that everything—nature, the universe, and even God—was all part of the same thing.
To them, the whole world was made of matter, but it was filled with something special called reason (they called it logos), which helps everything stay in order and work well. They saw fire as a symbol of this special energy because fire changes things, gives life, and spreads light.
The Stoics believed that each person has a little spark of this fire inside them, and our job is to live in a way that follows nature and reason. That means not getting too upset when things go wrong and not worrying too much about things we can’t control. Instead, we should try to stay calm and do what we know is right.
Stoics believed that everything in the universe is connected and happens for a reason.
That said, the Stoics thought we still have the power to choose how we respond. Free will and determinism can coexist, according to the Stoics. It’s like this: maybe you’re meant to walk through the red door instead of the blue one—but you still decide to do it because of who you are and how you think.
The Stoics taught that we can’t always change what happens, but we can choose how we react. That’s the real power.
Think about this: Is there something in your life that you keep trying to control, even though you can’t? What would happen if you stopped fighting it and tried to accept it calmly instead?
The Stoics saw destructive emotions—like fear, envy, or rage—not as natural inevitabilities but as errors in judgment. Our suffering, they believed, doesn’t come from events themselves, but from the way we think about them.
This idea is the root of modern cognitive behavioural therapy (CBT), which helps people challenge and reframe irrational beliefs. The Stoics were, in a sense, the world’s first life coaches—teaching people to reason their way to resilience.
Still, not everyone agreed with their approach. St Augustine famously rejected Stoicism with two words: Jesus wept. For Augustine, emotion was not a weakness but a mark of humanity. It’s a reminder that a balanced life may require not just control, but compassion—for ourselves and others.
Stoicism made its way into Roman hearts and minds, shaping the thoughts of figures like Cicero, Seneca, Epictetus, and finally, the emperor Marcus Aurelius. His Meditations, written on campaign in the cold forests of Pannonia, are perhaps the greatest personal testimony to Stoicism ever penned.
Marcus reminds us that even the most powerful man in the world grappled with mortality, temptation, duty, and doubt. And he found strength, not in conquest, but in philosophy.
Epicureanism: Peace through Simplicity
Epicurus built on the earlier atomism of Democritus and Leucippus. The universe, he claimed, is made of indivisible units—atoms—moving randomly through the void. There is no divine designer, no cosmic purpose. Instead, everything happens by chance. Even the gods, if they exist, do not intervene. They dwell in perfect detachment, indifferent to human affairs.
This worldview was radical. It removed the fear of divine punishment and destabilised the superstition-laden religion of the day. For Epicurus, liberating people from the fear of death and divine wrath was the first step to peace of mind.
The goal of life, according to Epicureanism, is not wealth, status, or even intense pleasure. It’s ataraxia—a state of deep, untroubled calm. This is achieved not by constant stimulation but by eliminating unnecessary desires and fears. Epicurus famously ate simply and lived quietly in a garden outside Athens.
Pleasure, in this view, is the absence of pain and disturbance. True pleasure comes from simple things: friendship, modest food, reflection, and freedom from fear.
“If you wish to be rich,” Epicurus said, “do not add to your money but subtract from your desires.”
Unlike Plato’s Academy or Aristotle’s Lyceum, Epicurus’ school met in a private garden. This was more than a location—it was a philosophy. He encouraged his followers to withdraw from public life, to avoid the turmoil of politics, and to focus on cultivating inner peace.
This has led some to view Epicureanism as selfish or escapist. But Epicurus would argue that real contribution comes from calm minds and free individuals—not from anxious, power-hungry politicking.
Question: In your own life, where might you need to step back in order to grow deeper?
If all reality is just atoms and void, then human hierarchies—kings, priests, aristocrats—are merely social conventions. At heart, we’re all made of the same stuff. This early materialism lent Epicureanism a quiet egalitarianism, not unlike the Stoic idea of universal reason.
It’s perhaps no surprise that Karl Marx wrote his university thesis on Epicurus. The idea that all change is driven by material forces—not divine will or heroic individuals—would have a lasting impact.
Epicureanism challenges our instinct to explain and control everything. It teaches that randomness is real, and that our attempts to predict or perfect the future often end in frustration or violence. Utopian projects that seek to build heaven on Earth can quickly descend into tyranny.
Instead, Epicurus invites us to live modestly, enjoy what we have, and expect less of the world—and of ourselves. There’s wisdom in resisting the pull of perfectionism and urgency.
Takeaway: Not everything has to be fixed. Some things just have to be accepted.
What matters is achieving ataraxia—peace of mind:
- Avoid unnecessary desires.
- Seek modest pleasures, especially friendship.
- Don’t fear death; it’s simply the end of sensation.
Though often misunderstood as indulgent, Epicureanism is about simplicity and inner contentment.
Prompt: What could you let go of today that would bring you closer to peace?
Conclusion: Ancient Questions, Timeless Wisdom
The ancient philosophers were deeply engaged and introspective human beings confronting the same kinds of questions we ask today:
How can I live well?
What truly matters?
How do I find peace in a world full of change?
Each school of thought offers a unique answer—together, they form a rich tapestry of wisdom that still speaks powerfully to modern minds.
The Ionians: Question what you think you know. Curiosity is the first step toward clarity.
The Eleatic School: Don’t just trust what you see—slow down and ask what lies beneath the surface.
Plato: In a world full of noise and opinion, seek what is timeless and true.
Aristotle: Wisdom grows through consistent action. Who you become is shaped by what you practice.
The Stoics: Let go of what you can’t control. Find strength in acceptance, and act with calm purpose.
Epicurus: You don’t need everything. Often, you just need less fear, fewer desires, and more quiet joy.
Though their views varied, these philosophers shared one belief: wisdom is meant to be lived. Their questions still matter because they are our questions too. In an age of distraction and uncertainty, their ideas give us tools to slow down, think clearly, and reconnect with what is truly important: living with integrity, using reason to guide our actions, finding peace through acceptance, and seeking joy in simplicity. These timeless teachings don’t provide all the answers, but they help us ask better questions—and that alone can provide us with a steady path forward.