When I was asked to prepare this volume for the series Fundamentals of Philosophy, I recognized that there are already a number of valuable introductory works on ancient Greek philosophy in the marketplace. I have created this volume in an effort to provide a work that will both offer a basic survey of the field in a historical sequence of the most influential philosophers, and present an opportunity to enter into the philosophical debates that those philosophers initiated or continued. This work is meant to be accessible to a large audience, but to be more than a primer; it aims to engage the figures as philosophers, with theories and arguments. Accordingly, I hope that this work will prove to be of benefit both to the new student of philosophy and to the professional philosopher, classicist, or humanist who, in the increasingly specialized world of academia, wishes to become better acquainted with this field.

Ancient Greek philosophy grows out of mythological lore, develops its own idioms and problems, and then develops into a sophisticated study from which originate philosophy, natural science, and many other disciplines that we tend to think of as modern inventions. Fortunately, the earliest philosophy begins without technicalities, and subsequent generations add gradually to the vocabulary and theory of the field, so that a historical study of ancient philosophy can introduce the complications of theory gradually and sequentially, as I have tried to do. Needless to say, no slender one‐volume study can do justice to the richness of Greek (and Roman) philosophy. I have provided in the endnotes references to important studies that can carry the reader on to more advanced studies of the material. I follow the story of Western philosophy from its pre‐philosophical mythological roots to its adoption by Christian philosophers who would transmit its messages to the Middle Ages. I have had to be selective in my coverage of thinkers and theories. But I have tried to cover the more important developments in philosophy, with some reflection on the social and political background they grew out of. I have also tried to indicate ways in which ancient thinkers carry on a conversation with their predecessors, and also offer valuable insights to their successors, including of course ourselves.

I would like to express my appreciation to Dr. Al Martinich for inviting me to undertake this project. This work was significantly improved by the suggestions of two anonymous readers, to whom I am indebted. I would also like to thank the editors and staff of Wiley, including Marissa Koors, Rachel Greenberg, Mohan Jayachandran, Manish Luthra, Deirdre Ilkson, Allison Kostka, Sindhuja Kumar, and Giles Flitney. I would also like to recognize my colleagues at Brigham Young University, a student research assistant, Michael Williams, and Michael Shaw of Utah Valley University, for advice and feedback on the project.

In the 460s BC a young Greek tourist made a journey up the Nile river in Egypt in search of answers. Among other things, he wanted to know what made the Nile flood, for it flooded at an odd time: in mid‐summer, not in winter or spring when the rivers in Greece flood with seasonal rains and melting snow. When he asked the local priests, they could tell him nothing, he reports. Perhaps they informed him that the Nile god caused the floods. But that was no answer. He went on to evaluate three different philosophical theories: the floods were caused by the summer winds that blew from the north and pushed back the Nile waters as they flowed northward, heaping them up; or they were caused by water flowing into the Nile from Ocean, a mythical watercourse flowing around the rim of the flat disk‐shaped Earth; or they were caused by melting snows in high mountains to the south. The young man rejected all these theories for their manifest failures to get the facts right, and he proposed a complicated theory of his own. At roughly the same time, a Greek sailor from Massalia went on a voyage that took him through the Pillars of Hercules to the west coast of Africa. He saw there a river with flora and fauna like that of the Nile and noted heavy winds blowing offshore, which he thought supported the second theory of the Nile floods.

The tourist, named Herodotus, went on to win undying fame as the Father of History.¹ The sailor, Euthymenes, wrote an engaging memoir of his travels.² Something strange was happening in the world. A tourist from Ionia (the Aegean coast of modern Turkey) and a sailor from Marseilles (Massalia was the Greek colony that preceded the French city) were traveling the world looking for evidence – scientific evidence, we could say – for theories about natural phenomena that everyone, including the Greeks, used to attribute to the workings of the gods. The idea of a rational explanation of the world based on natural processes rather than supernatural interventions was beginning to catch on. The proponents of the new approach we now call philosophers. Without them, the world we live in today would be immeasurably poorer.

1.1 From Mythology to Philosophy

There is a Latin maxim inspired by early Greek philosophy: ex nihilo nihil fit, nothing comes from nothing. That is a principle of Greek metaphysics, but it also offers a good principle of historiography. Every development has its antecedents, and it is the job of the historian to tell a plausible story of how we, or our predecessors, got from point A to point B. The starting point of our story is Greek mythology. Before there was a philosophical account of the world, there was a mythical account. The world arose in a theogony, a birth of the gods in which one cosmic god begot another and that god begot another. Eventually they quarreled with each other, fought a war, and Zeus emerged as the victor and chief god. In this approach, every important event that happens in the world is the work of Zeus and his companions. The sun is the chariot of the sun‐god Helios, which he drives across the vault of heaven every day. Lightning consists of missiles thrown by Zeus, the Cloud‐Gatherer. Earthquakes are the work of Poseidon, the Earth‐Shaker. (Some) plagues are caused by Apollo, the Far‐Shooter.

That is the starting point of the story of philosophy. Beginning around 600 BC a small group of intellectuals rejected the mythological story and pioneered a new way of thinking about the world. The major events of the world resulted, not from divine interventions, but from processes that are in principle like everyday processes we meet in our experience. These thinkers looked for naturalistic explanations of phenomena in place of supernatural explanations. Their theories were at first, by modern standards, crude. But their ideas developed with remarkable rapidity. In less than three centuries the successors of the first thinkers had developed many of the concepts we use in philosophy today, and some basic principles of science. In effect, they invented philosophy as we know it, and began to call themselves philosophers in the fourth century BC. In the next chapter we will have something to say about how this happened. But for now the important thing is that it did happen.

1.2 History and Philosophy

The early development of philosophy is indeed remarkable. But why do we even care about the ancient history of the field? Why not just do philosophy, as philosophers say, and forget about the boring ancient history stuff? Philosophers can be averse to history, interested only in the timeless interplay of ideas and propositions. Often we will discuss ancient philosophy ahistorically in this book: just treat ancient theories and arguments as if their authors were our contemporaries. The fact that we can do that shows just how contemporary ancient theories can be. And it allows us to think through problems with our predecessors.

But the ancient philosophers are not our contemporaries, and we need to appreciate them not only as peers but as contributors to an ongoing conversation that started with them. While we can debate any point in the present, there are certain assumptions that change over time for broadly historical reasons: people tend to believe in certain things in one age that they reject in others, and to interpret their experience accordingly. Think for instance of supposing that the Earth is the center of the universe, and that slavery is an acceptable or inevitable social institution.

For a long time philosophers pretty much ignored history. History, Aristotle said, deals with particular truths, whereas philosophy deals with universal truths. So philosophy is rigorously scientific while history is merely factual. It took another philosopher to convince philosophers that history was important: G. W. F. Hegel in the early 1800s. He went so far as to see history as the key to understanding philosophy. According to him, history reveals the unfolding of Spirit in time. There is a kind of logical progression of ideas as Spirit discovers itself in historical events, which will lead inevitably to self‐consciousness and the realization of Freedom. If we take Hegel seriously, there is a kind of March of History that leads in a virtually predetermined dialectical path to perfect knowledge.

What Hegel offered was the idea that there is a barrier between one age and another. Someone in Era 1 will tend to believe and understand things differently from someone in Era 2 at a later time. This is an important point. We tend to believe a great many things because our culture accepts them; no one can challenge all his or her community’s received beliefs (though Descartes notoriously tried his best to do so). So it seems unfair to be unduly critical of someone for holding the beliefs of his community. For instance, Aristotle believed that the Earth was the center of the universe; that women were inferior to men; that some people were natural‐born slaves. We can, of course, revile Aristotle for these views; but it seems unfair to do so. This is not, of course, to endorse his erroneous views. It is to recognize that he is a child of his time. Now there were, in fact, individuals who had questioned each of these views, even before Aristotle. But they were voices crying in the wilderness, and everyday “experience” seemed to confirm conventional beliefs to Aristotle and most of his contemporaries. (Before you start feeling too self‐satisfied about being enlightened, remember that someday people will look down on us for being so backward as to believe what we now believe.)

Some historians and philosophers have gone so far as to say that we cannot in principle have the same thoughts as someone from another time.³ This kind of historical relativism seems too extreme. We can, and good historians do, form sympathetic pictures of past people and events. We can also, and good historians do, make cogent historical judgments about past people and events. That is, in light of a sympathetic reconstruction, we evaluate them on the basis of present‐day standards. So we can defend some of Aristotle’s views as products of his time and his society’s beliefs, while wishing that he had been, for instance, as forward‐looking in his social theory as he was in his metaphysical and biological theories. The first step embodies a temporal, the second an atemporal approach.⁴ We first need to appreciate a past figure like Aristotle in light of his own times – and that includes understanding what problems he was trying to answer, and why – and then we can evaluate him in relation to contemporary expectations and developments. To skip the first part is to be unfair to our ancient subjects; to skip the second part is to become a mere antiquarian rather than a philosopher or historian.

Part of the challenge – and the fun – of studying the history of philosophy is trying to recognize new developments that become turning points in the history. Philosophy breaks off from mythology, so it starts out with no technical concepts, no real theory, of its own. In fact, philosophers seem to take for granted features of their mythological background – that the world has a beginning in time, and that the Earth is flat, for instance. Each new conception of the world tentatively advances new concepts, some of which become part of the vocabulary and background of philosophy and science. But, by the same token, early philosophy lacks the conceptual sophistication that we take for granted today. We are used to distinguishing between mind and body; thing and property; language, metalanguage, and reality; logic and metaphysics, and so on. But the early thinkers make no such rigorous or formal distinctions. How then do we read them? Do we apply our concepts to understand their theories or not? If we follow the distinction between temporal and atemporal studies, we will try to make sense of them in terms of their own time and intellectual context first; then we will try to fit them into our conceptual scheme – tentatively and reflectively, if possible. We need to recognize when we are putting new wine into old bottles, and old wine into new bottles. We change bottles at our own risk, but ultimately, we need to make the attempt if we are ever to understand our intellectual predecessors and ever to learn from them.

Here is an example. Modern philosophy (1600s to 1800s) is haunted by the Mind‐Body Problem that goes back to René Descartes: how does mind interact with body, and how does it know body? There is no such burning problem in the ancient world, though ancient theories do explore the relationship between mind and body. Anaxagoras is the first philosopher strongly to distinguish mind (Nous) from body; he says that a cosmic mind started a cosmic whirlpool that produced the world as we know it. He makes mind radically different from matter in some ways, for instance saying that every stuff is mixed with every other stuff, except for mind, which is pure and unmixed. Is he then a dualist, saying that mind and matter are utterly different? Not exactly. He does assign to mind physical properties such as location, and says mind is found in some things, especially living things. Plato for his part distinguishes between an immortal soul and a changeable body. He comes close to being a dualist, but he seems not to have a notion of persistent matter that could contrast in a strong sense with soul. Aristotle identifies mind as a function of soul, and locates soul in body, to which it is related as form to matter. But his own theory is complex and subtle enough that it is hard to characterize in contemporary terms, and indeed, different interpreters have attributed to him almost every theory of mind known to contemporary philosophy. So it turns out to be very difficult to answer what should be a straightforward question of classification about ancient theories of mind. This is not to say there are no answers to the questions, but only that the answers are not obvious or easy to come by. In fact, I will later argue that the ancients had a better take on the relation between mind and body than the moderns, and one which precluded much of the often barren debate and futile theory of the moderns.

One more historical issue is the matter of large‐scale historical developments. In his influential book, The Structure of Scientific Revolutions, historian and philosopher of science Thomas Kuhn (1996) argued that science does not progress in a linear fashion. Scientists follow paradigms, examples of scientific method that provide models for research. As long as the paradigm serves to solve scientific problems, a period of “normal science” continues. But eventually scientists run into problems that they cannot solve within the current framework. A period of “crisis” ensues which leads to a “scientific revolution,” in which a new paradigm emerges to inform normal science. Although Kuhn meant for this scheme to apply only to science, it seems to offer interesting parallels for the history of philosophy also. (Indeed, it is a kind of Hegelian scheme of eras of cultural unity punctuated by revolutionary episodes of change to a new era – though Kuhn does not explicitly draw on Hegel.)

There are times when philosophical discourse undergoes a radical change. One of the most celebrated changes of this sort is embodied in the life and thought of Socrates (as we shall see). Before him philosophy was largely carried out in didactic cosmological speculations (by thinkers who are now called, significantly, “pre‐Socratics”); after him in dialogues centering on ethical issues. Whatever the precise reasons for them, revolutions in thought are often recognizable in retrospect as turning points in the development of thought. There is a kind of disconnect (which Kuhn calls “incommensurability”) between practitioners of one kind of philosophy and those of another. Kuhn appeals to a political model of revolution carried out between advocates of a new ideology opposing the old establishment; communication between them may consist of propaganda and protests and rock‐throwing rather than rational debate. However that may be, it will be useful to keep an eye out for major shifts in philosophical theory from one era to another. As in politics and even science, the story of philosophy is not a simple stepwise progression from one idea to the next.

And this brings us to a final observation. There is always a temptation to see one idea as leading inevitably to the next, one theory to its successor, in a kind of “dialectical” progression, like that of a developing conversation. We find this pattern promoted already in Aristotle, who thinks that, “led on by the truth itself,” philosophy progressed from discovering one kind of cause to another (of his four causes).⁵ Hegel sees the progress of cultural and political history as embodying a logical dialectic, from thesis to antithesis to synthesis. This kind of March of History story would turn history into a science, as Hegel believed it would, and make all developments rational and inevitable. But alas, the course of history seems a good deal messier than the Aristotles and Hegels of the world recognize. In particular, the history of philosophy has its own contingencies that are neither predictable nor fully explainable.

Yet a good historical account makes sense of the developments of philosophy in such a way that the later events are seen as reactions to the earlier ones, and some kind of at least relative progress is perceivable from the earlier to the later theories. And that progress results largely from a kind of internal dialectic or conversation, rather than from external economic, political, or social factors. In ancient philosophy we shall see a rapid conceptual development from primitive, almost mythological ideas, to sophisticated theories, some of which have never been surpassed in their power and elegance. In what follows, we will trace the broad development of theories, focusing at various points on interesting problems and arguments that made the ancient conversation so rich and fruitful, and so philosophically interesting. And we will see that philosophy is at some level an ongoing conversation in which new theories grow out of attempts to solve old problems in new ways. However timeless our contemporary theories may seem, they always arrive schlepping baggage from the past, and depart leaving new baggage for the future.

1.3 Overview

Here then is a preview of the stages of development of ancient Greek and Roman philosophy as we will discuss it, with some of the important ideas that arise.

First of all the Greeks, like peoples of all cultures at the same time, had traditional tales about the origins of the universe and the gods who peopled it, along with the rise of the human race (Chapter 2). In the sixth century BC, in the city of Miletus on the Aegean coast of Anatolia (modern Turkey), some thinkers proposed a naturalistic account of the origins of things. While this account assumed some of the features of the world accepted by tradition (the Earth was understood to be a flat disk surrounded by water, for instance), it explained the world as the product of natural processes rather than divine births and supernatural interventions. These thinkers did not, so far as we know, have any special name for what they were doing, but in time it came to be known as philosophy, and the early thinkers were designated (in modern times) as Presocratic philosophers (philosophers before Socrates), who marked a turning‐point in thought. In the earliest models of speculation, the world was thought to be composed of basic or elemental stuffs that turned into each other. In one version, fire was the rarest kind of matter, that, when it was condensed, turned into air; when air was condensed, it turned into wind; when wind was condensed, it turned into cloud; when cloud was condensed, it turned into water; when water was condensed, it turned into earth; when earth was condensed it turned into stones. And this process could be reversed, so that denser materials would be transformed into lighter materials by rarefaction. The earliest philosophers tended to pick one of their stuffs as the original stuff from which all the others derived; for instance, Thales chose water, Anaximenes air. This picture of reality allowed philosophers to propose cosmological theories, in which the world as we know it arose out of the transformations of matter, which, when they became stabilized, constituted the present world, with its ecology. For instance, water evaporates from the sea, condenses into clouds, and rains onto the Earth. From the natural world arose plants and animals, and eventually human beings, who developed cultures and technologies that allowed them to thrive. So the product of this thinking is a kind of scientific philosophy with a speculative chemistry, cosmology, biology, and anthropology – that in some crude way anticipate modern scientific theories.

This model was challenged by Heraclitus, who pointed out through his paradoxical utterances that on this model all the stuffs were equal and interchangeable. If this was so, there could be no original stuff, but only the eternal process of change. What was ultimate then, was not the stuffs, each of which was a temporary state of affairs, but the pattern of change itself.

Subsequently, Parmenides, writing a philosophical poem in the early fifth century BC, probably in reaction to Heraclitus’s criticisms which stress the ephemeral character of stuffs, argued against the possibility of change, and against the notion that things could change their characters. His theory seemed to be that reality consisted of one unchanging being. It is possible, however, that he argued for a weaker thesis that whatever existed had to have an unchanging nature. At the end of his poem, Parmenides presented a cosmology of his own in which two distinct stuffs, which he calls Light and Night, a rare and a dense substance, respectively, mixed in different proportions to produce all the objects we are acquainted with. On the one hand, Parmenides implied that this cosmology is unknowable; on the other hand, he offered it as superior to all others. Whether he meant it to be a refutation of any possible cosmology or a model for how speculative cosmology might be done, his successors seem to have taken it in the latter sense. In fact Parmenides offered some brilliant observations on astronomy as part of his cosmology, that turned out to be right and ultimately revolutionized the study of astronomy.

Parmenides’s theory offered the model of permanent elements that by combination and separation could produce temporary compounds. Philosophers writing after Parmenides did not abandon cosmology (except for a few followers of his), but rather proposed more elaborate theories of elements. Empedocles posited four elements: earth, water, air, and fire, a theory so influential that it lasted until about AD 1600. These corresponded roughly to the great cosmic masses of Earth, sea, atmosphere, and fiery heavenly bodies, and they could be supposed to combine to form all other stuffs, including flesh, bone, wood, and iron. About the same time, Anaxagoras posited an unlimited number of elements that could mix together or emerge as the dominant member of the mixture. The most powerful theory that appeared in the fifth century BC was that of the atomists, Leucippus and Democritus, who posited microscopic particles of matter of different shapes that could combine into objects of all kinds.

In the second half of the fifth century BC, a new movement arose of itinerant teachers known as sophists, who traveled about the Greek world lecturing and attracting (paying) students for short courses. The sophists were steeped in the cosmological theories of their predecessors, and some of them taught such theories to wide audiences, but mostly they offered “practical” subjects that were in demand in the new democracies that arose in this period: public speaking, political theory and practice, and financial management. Some sophists promised that their students would learn to win any debate they entered into. These kinds of claims raised ethical issues of whether one could win an argument even when one was defending a falsehood. Indeed, some sophists raised questions concerning whether good and evil, right and wrong were natural concepts, or whether they were human inventions.

Here we meet Socrates (Chapter 3), who arose out of the same culture as the sophists but challenged their sometime immoral or amoral teachings. Unlike the know‐it‐all sophists, he professed not to have any special knowledge. Yet he made tireless efforts to discover the nature of virtue and concepts of right and wrong, asking what virtue was and whether it was teachable (as the sophists assumed it was). Socrates’s question‐and‐answer method and his careful analyses of ethical concepts turned philosophy away from cosmological speculation on the one hand, and from education for political success on the other. In the tumultuous age of the Peloponnesian War which pitted Greek city‐states against each other and brought out some of the worst of human passions and hostilities, Socrates was the self‐appointed gadfly and conscience of his home city of Athens. Somehow, despite his claims to lack any special knowledge, he managed to live a life of spectacular virtue, standing up to the powers of his city a number of times on matters of moral significance. Although he wrote nothing and claimed not to be a teacher, he gathered around him a number of brilliant young men who would carry on his movement into the fourth century BC. When he was accused of impiety and corrupting the youth and put to death by the democracy, his followers vowed to vindicate their master.

Soon after Socrates’s death, his students began publishing reminiscences and fictionalized conversations in a new genre, philosophical dialogues, which recreated the philosophical discussions of their master. The most successful of these students, as a writer, philosopher, and teacher, was Plato (Chapter 4). Plato seems to have had the philosophical acumen to understand Socrates as many of his other followers did not. And his literary skills allowed him to bring Socrates to life as no one else could. Plato contributed many of the dialogues that portrayed Socrates. As a citizen of Athens, Plato also had political ambitions. But his early experiences with the government of the Thirty (see Chapter 4) and with the trial and death of Socrates turned him into what Socrates never admitted to being, a professional philosopher. Plato founded the Academy, which gathered many of the brightest minds of Greece. His own works were almost all dialogues, mostly featuring Socrates as the protagonist. But scholars have identified works that seem to present Socrates’s ideas and methods, and those that present Plato’s ideas and methods. In the latter works, Socrates becomes a mouthpiece for Plato rather than a recreation of the historical figure.

Whereas Socrates was exclusively a moral philosopher dealing with ethical issues, Plato saw a need to support moral philosophy with a strong theory of knowledge (epistemology), a strong theory of reality (a metaphysics), and a theory of the soul (psychology). He posited the existence of eternal realities he called Forms, such as Justice itself, Equality itself, and Goodness itself. He treated abstract concepts such as these as ultimate beings. He viewed the world we live in as a world of Heraclitean change with no permanence. Whatever order and constancy it had, it owed to a connection with the Forms, which he called “participation” or “imitation.” He believed that humans have eternal souls that inhabit human bodies through a cycle of reincarnations. When the soul was outside the body it was more in touch with the Forms than when it was in the body and distracted by its needs. The human soul in a mortal body had a dim awareness of the Forms; by a process of “recollection” it could come to reacquaint itself with the Forms themselves and appreciate them more fully. Plato saw Socrates’s question‐and‐answer method as providing the means to help us rediscover the Forms.

Plato went on to develop the political theory, a theory of art, a theory of education, and many other theories grounded in his Theory of Forms and its attendant principles. Plato offered the first comprehensive theory of everything in the Western tradition.

Plato’s most important student was Aristotle (Chapter 5), an orphan from an important family in northern Greece. Aristotle spent 20 years in Plato’s Academy and then, on Plato’s death, lived in northern Greece until the last part of his life, when he returned to Athens to found his own school, the Lyceum. It appears that even as a young student Aristotle was critical of Plato’s Theory of Forms, and he invented or developed a number of important objections to the theory. According to Aristotle, the ultimate realities were not abstract entities but concrete things such as Socrates the human and Fido the dog. Aristotle provided the first rigorous ontology, or theory of basic realities, in which he distinguished between individual things (“particulars”) and general types (“universals”) on the one hand, and things (“substances”) and properties (“accidents”) on the other. For Aristotle, the ultimate realities were in the class of particular substances, whereas universal substances and properties were dependent for their reality on particular substances. Thus Doghood exists because things like Fido and Fifi exist, and not vice versa; and Justice exists because there are just people like Socrates and Pericles. This allowed Aristotle to advertise himself as a philosopher of common sense who believes in realities we are all acquainted with, rather than being forced to posit mysterious entities such as Platonic Forms or Democritean atoms, which are not accessible to us.

While Plato offered the first comprehensive philosophy, Aristotle offered the first systematic philosophy. He invented the first theory of logic, which he applied to the philosophy of science. He developed his own cosmology, biology, meteorology, psychology, ethics, political theory, rhetoric, philosophy of art, and so on. While Plato covered some of these areas (he shied away from scientific theories in general), Aristotle was unique in compartmentalizing areas of study so that they could be studied rigorously and in depth. Where Plato tended to offer wonderful analogies like those of the Sun, the Line, and the Cave in the Republic, Aristotle offered rigorous argument for almost all of his claims. In retrospect, he was wrong in many of his theories; but he never assumed anything, and rarely let an image stand in for an argument. He seems to have thought of everything and to have covered all his bases when he presented a theory. When his works were recovered in the late medieval period, philosophers tended to be overwhelmed by his system and to accept it as gospel truth. Although Aristotle was a prodigious scientific researcher who, for instance, studied numerous zoological species in the field, collected specimens he dissected, and made important astronomical observations, many of his medieval followers knew him only as a theorist.

After the death of Aristotle, Athens became the home of new movements in addition to the schools of Plato and Aristotle (Chapter 6). The Hellenistic period, after Alexander the Great’s conquest of the Persian Empire, was a time when Greek culture was exported throughout the Mediterranean and Middle East. Philosophers in Athens attracted students from around the world. Epicurus accepted the natural philosophy of the atomists, but now filled it out with an ethical theory. Epicurus advanced a value theory according to which the good life consisted of pleasure, or, to be more precise, the absence of pain. This drive to avoid pain he saw as the key to all motivation. He advocated a life of moderation, which precluded an active involvement in politics. He modified atomic theory by saying that sometimes atoms make a random swerve, which provides the possibility of free will by avoiding determinism. About the same time Zeno of Citium came to Athens. After studying with the Cynics, who were followers of a student of Socrates, he founded the Stoic school. This school was almost the polar opposite of the Epicurean school. While the Epicureans believed in free will, the Stoics believed in determinism, the view that all events were determined by earlier events. Whereas the Epicureans believed that matter consisted of atoms and the void, the Stoics believed that matter was continuous, with no void. While the Epicureans followed the physical theory of the atomists, the Stoics followed Heraclitus, and claimed that everything was fire. They also held up Socrates in particular as a model of the life of virtue and reason. They had an ideal of the Stoic sage, who would possess all possible knowledge.

At about the same time as the Epicurean and Stoic schools were founded, a movement of skepticism arose. Plato’s Academy, surprisingly, became a hotbed of skeptical ideas, as Academics read Plato’s Socratic dialogues as showing that there were no adequate answers to philosophical questions. Pyrrho of Elis taught a skeptical philosophy at about the same time. He did not leave any writings, so, as with Socrates, he can be known only through reactions of his followers. Both versions of skepticism challenged the possibility of having knowledge of philosophical truths. They tended to find tranquility not in philosophy, but in rejecting philosophical speculations.

During the Hellenistic period, Plato’s idealistic philosophy was eclipsed by skeptical interpretations. But from the first century BC, it was revived as Middle Platonism, which borrowed features from Aristotelian and Stoic theories and emphasized religious aspects of Plato’s philosophy. In the third century AD, the philosopher Plotinus from Alexandria, Egypt, moved to Rome and began to teach his own version of Platonism which has come to be known as Neoplatonism (Chapter 7). He interpreted Plato as believing in four levels of reality, or hypostases: the One, which was a transcendent god; a cosmic Mind, in which the Platonic Forms were located; a World Soul; and matter. Each higher reality overflowed or radiated to create a lower level of reality below it. Plotinus, like Plato, believed in reincarnation. He saw the individual soul as falling through a kind of original sin of self‐assertion so as to come into a physical body. By a process of purification through dialectic, the soul might eventually free itself from the cycle of rebirths. Neoplatonism became popular among intellectuals and eventually replaced most of the other philosophies – with the exception of Aristotelianism, which Neoplatonists saw as compatible with their brand of Platonism.

Middle Platonism found adherents not only among pagans, but among Jews such as Philo of Alexandria and Christian “Church Fathers” such as Clement of Alexandria and Origen (Chapter 8). With the growth of Christianity, Christian thinkers found common ground with pagan intellectuals in certain kinds of philosophy. Eventually, Christians created their own theology on the model of philosophical theologies, and Augustine of Hippo (who would become St. Augustine) finally constructed a system in which philosophy was Christianized, and Christianity supplied the theology. Augustine rethought some classical philosophical problems in light of Christian revelation, and provided the beginnings of a philosophical tradition for the Middle Ages.

In what follows, we will trace the growth of philosophy from its beginnings to the end of the ancient world, observing the introduction of new concepts, theories, and methods that will take us to increasingly sophisticated conceptualizations of the world. We will observe anticipations of many contemporary philosophical and even scientific theories.