Everything you always wanted to know about Greek philosophy

A very short but compelling tour of the major ideas that shaped western thought

Some of the ancient Greeks, from left to right: Homer, Thales, Pythagoras, Heraclitus, Socrates, Plato, and Aristotle; image from greecehighdefinition.com.

My academic semester is just about to end. Indeed, today will be my last class. Not only that: I’m about to go on sabbatical, which means that I will neither teach nor participate to administrative meetings for the entire 2023. Just reading and writing about Hellenistic philosophies and about Cicero, the topics of two books I intend to write while traveling in Rome, Syracuse (Sicily), Western Turkey, and Athens.

But that’s what is to come, fate permitting. The inspiration for the current essay is the course I just finished teaching at the City College of New York: Philosophy 30500—History of Philosophy, Ancient. It’s a course that is aimed mostly at students majoring in philosophy, and I had never taught it before. For good reasons, since I’m not a scholar of ancient philosophy. My specialty is philosophy of science.

But my Department’s Chair asked me to teach 30500 because of the popularity of my courses on practical philosophy, which focus on the Greco-Romans. I accepted the challenge, and it surely was a lot of fun! As textbook I used Thomas A. Blackson’s Ancient Greek Philosophy: From the Presocratics to the Hellenistic Philosophers. And both my students and I learned a lot in the process.

This also was a rare opportunity—precisely because I am external to the field and because it was the first time I taught the course—to look at the entire subject matter with fresh eyes. What follows is a summary of what I think are the major ideas coming out of Greek Classical and Hellenistic philosophy, a sort of mini intellectual tour de force that should make it clear why it is still very much worthwhile to study what they thought. Enjoy!

The period covered by the course goes from 585 BCE, when Thales of Miletus was the first one to predict an eclipse of the sun, to 529 CE, when the Christian emperor Justinian prohibited the study of philosophy and closed all non-Christian schools, including the last classical school then still standing, Plato’s Academy. We are talking about one full millennium of thinking about the major questions that have preoccupied humanity: what is the true nature of reality? What is our place in it? How should we live, and why?

Naturally, we begin with the so-called Presocratics, a name that still today implies the pivotal role that Socrates of Athens had in the development of western philosophy. We recognize a number of schools and trends within the Presocratics:

The Milesian school (after the city of Miletus, modern western Turkey) was the one that began philosophy as we understand it, taking the extraordinary step of turning away from poetic and mythological explanations of events (think Homer and Hesiod) in favor of naturalistic ones. This was, essentially, also the beginning of science. The Milesians thought that experience is the basis of knowledge, thus beginning the long tradition of empiricism in philosophy. The three main figures were:

Thales, who arrived at the conclusion that the ultimate structure of reality was water;

Anaximander, for whom everything is a manifestation of something that he called the apeiron (usually translated as infinite, limitless);

Anaximenes, who thought that air is the foundational element.

The Stoa of Miletus, photo by the Author.

A second major Presocratic group is usually referred to as the Eleatic school (from the city of Elea, in present day Campania, Southern Italy). Its members thought that reason is the basis of knowledge, thus inaugurating the rationalist tradition in philosophy. The two major exponents were:

Parmenides, according to whom nothing comes into or goes out of existence;

Zeno (he of the logical paradoxes), for whom movement is an illusion.

The Eleatics are crucial because they introduced the notion that reason can override sensorial experience to yield counterintuitive conclusions. This is, of course, a major characteristic of modern theoretical science, especially fundamental physics.

Four more Presocratics defended and expanded what became known as the inquiry into nature (i.e., science):

Heraclitus, for whom fire was the fundamental element, and who famously said that we cannot step into the same river twice, because the world is not made of static things, but rather of continuous processes, an approach known today as process metaphysics.

Empedocles, who taught that everything is transformation, and that the world as we see it is the result of the dynamic balance between two fundamental forces that he called Love and Strife;

Anaxagoras, who suggested that the ordering principle of the universe is a Cosmic Mind (Nous);

Democritus and Leucippus, the atomist philosophers according to whom the structure of reality is made of fundamental particles which, when combined in different ways, yield the macroscopic world we normally perceive.

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Socrates is, of course, the pivotal figure in ancient Greco-Roman philosophy. He broke from the Presocratics, turning his attention from nature to human beings. No metaphysics and natural philosophy for him, but ethics and politics instead.

He introduced the notion that happiness (eudaimonia) is the result of a certain psychological state, an idea that will be retained, though in different guises, by Plato, Aristotle, and the Hellenists that will follow.

Socrates was interested in definitions, always going around asking what is the X-ness that is common to all instances of X? For example, what makes just things just, or pious things pious? He wasn’t fixated with dictionaries, but thought that if we don’t have a clear idea of what we are talking about, perhaps we shouldn’t talk about it…

My class examined three Platonic dialogues:

Euthyphro, on the nature of piety, where we learn about the famous dilemma: is something moral because the gods say it is, or do the gods say that something is moral because it, in fact, is? In the first case, morality is arbitrary, a matter of might makes right. In the second case, there is a source of moral knowledge that is independent of the gods. Either way, the gods are not were true morality comes from.

Apology, on the nature of the love of wisdom (i.e., of philosophy itself). It concludes that the good life for a human being is a life of virtue.

Protagoras, where we learn that virtue is a type of expertise, like playing an instrument, and that it can be learned (and taught) accordingly.

Socrates, National Roman Museum, Rome, photo by the Author.

We then turned to the Sophists, which Plato presents as Socrates’s nemeses. We looked in particular at two Platonic dialogues:

Protagoras (same as above, but now paying more attention to what Protagoras, rather than Socrates, says).

Gorgias, where Socrates attempts to get a definition of rhetoric, the art taught by the Sophists, in order to explore its relationship with virtue.

Socrates thinks the Sophists are merchants, they sell you a way to get what you want, not wisdom and virtue. The art of persuasion (Sophistry, rhetoric) is not the same as the love of wisdom, and indeed it is antithetical to it, because rhetoric does not concern itself with what is good, and therefore it can easily be misused.

The big underlying contrast is between a life of pleasure and a life of virtue.

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Moving on to Plato, we discussed three of his most important contributions to philosophy:

I-The theory of recollection, in the Meno

What we call “knowledge” is actually recollection from previous lives, which shows that our souls are immortal. As we would put it today, knowledge is innate, or instinctive. Socrates shows this by way of eliciting a geometrical proof from a young slave who couldn’t have known anything about geometry.

False beliefs are caused in us by the trauma of reincarnation (Plato here was influenced by Pythagoras). To counter the problem, we need to pursue the love of wisdom, i.e., philosophy.

Moreover, virtue cannot be taught, a fact made clear by the absence of teachers of wisdom and by the observation that the sons of virtuous men are rarely virtuous. (However, remember from above that in the Protagoras, Socrates arrives at a different conclusion: virtue is a technical skill, like playing music, and it can therefore be taught, though not just as theory. It requires practice.)

II-The theory of Forms, in the Phaedo

The goal of a lover of wisdom is to grasp the Forms, the immutable and universal models underlying all of reality.

The disembodied soul is naturally capable of grasping the Forms. The body, however, gets in the way of such abstract knowledge, because it hinders our intellect. Happiness, therefore, lies in contemplation of the Forms, which is the activity that brings us closest to the blissful state of a pure soul.

III-The tripartite theory of the soul, in the Republic

There are three components to the soul: rational, spirited, appetitive. These correspond to the three classes of the ideal republic: guardians, soldiers, workers.

The soul is harmonious when reason is in control, as a charioteer controls his horses. Again, this is a psychological theory of happiness.

Analogously, at a macrocosmic level, the republic is just when the guardians are in charge. It follows that justice, harmony, and happiness are aligned: the state is a macrocosm of the individual.

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Aristotle distinguishes “First Philosophy,” i.e., metaphysics, the discipline that studies “being as being” and “Second Philosophy,” i.e., what we call science (physics, biology, etc.).

The material that constitutes a natural body is organized so that there exists a body that instantiates the natural kind to which the body belongs. “Human,” for instance, is a natural kind, of which we are all particular instantiations.

Natural bodies have a function or purpose (teleology). For example, the human eye is for seeing; the sapling is destined to develop into an adult oak tree; and so on.

Aristotle rejected Plato’s notion of Forms as independently existing. A Form is simply the pattern that shapes natural objects, it can only exist in a physically instantiated state.

The universe was set in motion by an Unmoved Mover, which could be interpreted as God or as the set of laws of nature.

Like both Socrates and Plato, Aristotle assumes that human happiness is the result of correct psychological functioning.

While for Socrates happiness results from self-examination and for Plato it stems from the contemplation of the Forms, Aristotle thought that there are two sources of happiness:

I. Contemplation, where we attempt to be as much as possible as the Unmoved Mover;

II. Engagement in politics, because we are fundamentally social animals.

Contemplation and politics are proper functions of the human animal: we are rational and social. That said, Aristotle ranked contemplation higher than politics as a source of happiness.

He also made a distinction between theoretical and practical wisdom: the first refers to things that could not be otherwise (theology, “physics”—i.e., science—, and mathematics), while the second one refers to things that could have been otherwise (everything else, including ethics).

Theoretical wisdom about theological matters is the most important because, again, it gets us closer to the Unmovable Mover.

The goal of practical wisdom, by contrast, is to align our desires with the dictates of reason and away from the urges of the spirited and appetitive souls.

Again, two sources of happiness result: a life of the intellect (higher), and a life of virtue. These correspond to contemplation and politics.

But what is virtue? It is the (reasonable) middle between two extremes. For instance, courage is the middle way between cowardice and rashness. Virtue results from experience and practice.

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The Hellenistic Age is the period from the death of Alexander in 323 BCE to the end of the Roman Republic in 31 BCE (battle of Actium, where the future emperor Augustus defeats the combined forces of Mark Anthony and Cleopatra, ending the Roman civil war). This is a period of great cultural and political change, which is probably what spurred the flourishing of many alternative philosophies of life.

The Epicureans rejected the Socratic-Platonic-Aristotelian primacy of reason and positioned themselves instead within the empiricist tradition, thus arching back to the Milesian School.

They also rejected the classic, virtue-based, conception of happiness. Happiness has to do with pleasure, and the highest pleasure—somewhat counter-intuitively—is lack of pain (both physical and mental).

A major source of mental pain are myth-induced fears of gods, death, and the afterlife. We have no reason to entertain any of those.

The Epicureans proposed a fourfold remedy (tetrapharmakos) for a happy life:

I. God presents no fears,

II. death no worries.

III. And while good is readily attainable,

IV. bad is readily endurable.

The ultimate goal is peace of mind, ataraxia.

Epicurus, National Roman Museum, Rome, photo by the Author.

The Stoics—against Plato and Aristotle—went back to a Socratic understanding of human reason and happiness: we always do what we want to do, therefore, when we do bad things it is out of ignorance, not “weakness of the will” (as in Aristotle).

Cognition and emotions are not separate, the soul is unitary. Fear, for instance, is the result of our own interpretation of external events and their meanings. Hence Epictetus’s famous statement that what disturbs us are not events, but our opinions about events.

Children naturally aim at self-preservation, and they soon understand that self-preservation is made possible by cooperating with others. We are eminently social animals. Reason then allows us to expand our natural circles of concern beyond our immediate relatives, friends, and acquaintances. Ideally, up to encompassing all of humanity (cosmopolitanism). This is what modern psychologists would call a theory of cognitive development.

The Stoics too put forth a psychological theory of happiness: it consists in living according to nature, which means rationally and prosocially.

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Academic Skepticism began in 268 BCE with Arcesilaus. He reinterpreted Plato and the Academy in terms of the Socratic practice of exposing the pretense to wisdom in those who put themselves forward as experts.

The skeptics engaged in a longstanding debate with the Stoics about epistemology: according to them, and contra the Stoics, there are no “kataleptic” impressions, that is, no sure mark separating true from false perception. Therefore, it is wise to suspend judgment.

Carneades introduced the concept of pithanon (persuasiveness), which Cicero translated as probabilis, from which the English probability. Impressions can have four degrees of persuasiveness. In order of increasing probability: apparently true > convincing > undiverted (meaning that they cohere with other things we know) > thoroughly explored (as a result of active investigation on our part).

Cicero, Capitoline Museums, Rome, photo by the Author.

The other kind of skepticism is known as Pyrrhonism. It is characterized by:

Epistemology: we don’t know whether we really know or not.

Practice: suspension of judgment on all things that are “non-evident.”

Goal: tranquillity of mind (ataraxia)

Agrippa introduced the famous Five Modes leading to suspension of judgment:

I. Dissent – Different people have different opinions on any given topic, so we shouldn’t be too confident in endorsing one opinion over another.

II. Infinite regress – Any assertion requires justification, which in turn requires justification, and so forth without end.

III. Relative perspective – As we look at things from different points of view we perceive them differently, so we shouldn’t be sure of the preeminence of one perspective over another.

IV. Assumption – The truth asserted is based on an unsupported premise, which is taken for granted.

V. Circularity – The justification of an assertion is found in another assertion, which is then justified by yet another assertion, until one or more of the assertions already examined are invoked again.