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Socrates, Plato, Aristotle


‘What would Plato do?’

Jamie Lee Curtis in the film ‘A Fish called Wanda’ (1988)


‘Philosophy begins with wonder’

Plato – Thaetitus . . . as said by Socrates

The Parthenon – An icon of the West

What did clever people who lived more than 2000 years ago think about life, the universe, and everything?
The Acropolis hill topped by the Parthenon as it is today.
Image: Roger Spencer- June 2014

Framing existence

Questions about individuals and society and the best way to live our lives – along with concerns about fundamental categories of being . . . what exists, the nature of mind and matter, causality, what we can know with certainty, identity, consciousness, ethics . . . these have been with us since the dawn of humanity.

Has anyone ever known how to answer such questions? Has anyone ever made any headway in making sense of everything . . . or said anything worthwhile about these building blocks of our existence? Questions like these might seem unanswerable, even a waste of time, but the attempt to answer them has generated the entire body of human knowledge. Answers to such questions have come from two main sources: science and religion.

In Western society a few people have looked long and hard at these types of questions and made an honest attempt to find solutions, their thoughts written down for posterity as justifications for the categories that we use to describe and explain everything.[8] Three men in particular stand out in this tradition – Socrates, Plato, and Aristotle – who lived in Ancient Greece over 2000 years ago in a brief period when thought ranged freely over the whole spectrum of human concernsbut without drawing inspiration and ideas from conventional sources of knowledge like the unjustified trust or faith of religions and dogmas that did not provide reasons, or by deferring to the the power of tradition and social authority. Their conclusions were considered so ingenious and insightful that for many years they formed the core of the Western education system known as the ‘classics’.

By writing the first formal treatises on many subjects Aristotle established a curriculum of study that has persisted to this day. From the ancient Greeks we get words like philosophy (philosophia), mathematics (mathematike), physics (phusike), history (historia), geography (geographia), politics (politike), economics (oikonomia), democracy (demokratia), theatre (theatron), music (mousike), and aesthetics (aisthetika) and their work in these subjects has flowed into present-day science, medicine, astronomy, logic, engineering, ethics, law, architecture, sculpture, literature and much more. Perhaps more than any others, these men constructed a framework of mental categories round which we could build our understanding and explanations of existence.

We call these men philosophers (‘philosophy’ in their day referred to all knowledge) in a tradition that passed from Socrates (469-399 BCE), his pupil Plato (c. 427 or 423-348 BCE) and, in turn, Plato’s pupil Aristotle (384-322 BCE). Of special interest to us in the articles on this web site is that Aristotle was followed by a plantsman Theophrastus as head of the Lyceum in ancient Athens. These men are not so popular nowadays but their thoughts over 2000 years ago, I am sure, will never cease to impress those who genuinely want to understand life’s big questions. I hope that after reading this article you will understand why that is so, and also understand the distant origin of questions that remain fresh and important to us today.

As with all knowledge, these men were building on what existed before as part of a written tradition that only remains today as fragments and the reports of others.


The ancient Greeks ruled an empire with colonies that extended from the eastern Mediterranean to Sicily that was divided into politically autonomous city-states that had many different kinds of self-government.

The three great men we are considering were building on the earlier thinking of philosophers from Greek colonies on the present-day coast of western Turkey (Anatolia) known as Ionia which seems to have adopted many characteristics of the earlier Minoan civilization that had existed on the island of Crete. In Ionia there were major urban centres at Miletus and Ephesus.

Other communities had developed in coastal southern Italy (known to the later Romans as Magna Graeca) where there was the Pythagorean school famous for its mathematics.

These two schools were closely associated with the sharing of ideas that would have resulted from the trade that passed between East and West and  the coastal cities of the Aegean Sea in the eastern Mediterranean.

They wondered whether the world consisted of one underlying substance (monism) or many (pluralism); whether  there were foundational factors in the world and, if so, whether underlying factors were physical and/or  immaterial. Part of the questioning concerned the ordering of things and whether the apparent cosmic order implied a moral order (a theme later taken up by Hesiod, Sophocles and Aesculus).

Athenian Greeks called these early philosophers physiologoi, although Aristotle called them physikoi from the word physis, meaning ‘nature’ and the source of our word ‘physics’. They mostly shared the belief, common to today’s scientists, that the world exhibited the properties of investigable order (logos) and constant flux (change). The pre-Socratics sought to understand and explain the inner workings of matter and the principles that govern its transformation and combination. Though they rarely performed experiments and, we would now say, were incorrect in their conclusions, they do resemble modern scientists in much of their methodology and are therefore considered to be the natural scientists in the western tradition.

Democritus, for example, was a qualitative monist (everything consists of identical indivisible units of physical matter called atoms) but a quantitative pluralist (these atoms are many). The diverse world of today, he believed, was formed by chance combinations of atoms giving rise to the mechanistic materialism, the idea of science studying matter in motion often used as a characterisation of science in the Scientific Revolution. In contrast Anaxagoras believed in ‘nous’ as an immaterial ordering, a kind of immaterial directedness or teleological force.

The pre-Socratics were mostly revisionists who tried to provide explanations of the world by accounting for change not in terms of supernatural forces such as the will of the gods but in terms of the intrinsic nature of material things, and they defended their views with rational argument. The world for them, as synthesized by Empedocles (c. 495–435 BCE), consisted of the elements Earth, Air, Fire, and Water although the significance and ranking of each of these elements varied according to each philosopher. These elements were fundamental constituents for life – the earth providing food, but air and water also essential along with fire for warmth and cooking. The final or ultimate element or principle was then usually assigned a divine or god-like status.

We associate Heraclitus with the detailed study of change while Parmenides and his student Zeno were monists who challenged the pre-Socratics by denying the reality of change using powerful rational arguments that have challenged philosophers up to the present day.

Plato recognised the absurdity of an anthropomorphic god ruling the universe from outside like an authoritarian father. He understood the divine not as supernatural but transcendental (beyond experience but not beyond knowledge) – the divine was the ultimate principle of the inner workings of the cosmos . . . the intelligible order as an ultimate reality. It was the task of the philosopher to look beyond our world of appearances to understand and explain this inner order to the best of their ability.

The pre-Socratics also posed the question ‘How are we to live good lives if the gods are not telling us what to do? a question that would be taken up by the later Greek philosophers. Emphasis on naturalistic (non-supernatural) explanations led to these men being called natural philosophers although it may be more accurate to call them simply the pre-Socratics as religious views still played some part in their thinking. Many of their ideas seem quaint and wrong-headed to us today but their rigorous disputation provided a methodology used by the five special philosophers discussed in articles on this web site, and their way of explaining the natural world analytically in material and rational terms was a kind of proto-science. The hallmark of this naturalistic philosophy was to avoid the tradition of inserting the divine into all explanation. Planetary motion was, for example, examined in natural terms rather than simply accepted as being a consequence of God’s will.

Intellectuals of ancient Egypt and Babylon had used mathematics to predict the movement of the planets, assembled detailed star charts, and calculated the areas and volumes of different shapes, a skill cleverly applied in the construction of the pyramids. This would lay the foundations for future geometry. Before 3000 BCE Egyptians had developed a 365 day calendar year to assist in predicting the annual floods of the Nile. Babylonian mathematicians used a base-60 system that we still use for time and degrees of the compass and Mesopotamians developed logarithmic tables, algebra and quadratic equations and made detailed observations on the movement of planet Venus. When the Babylonian Empire collapsed in 612 BCE some of the Babylonian scholars travelled into the eastern Aegean, especially Ionia, where a fusion of old Mesopotamian learning and new Greek ideas resulted in the Ionian Enlightenment.


Among these pre-Socratics was the philosophical school at Miletus which discussed the fundamental ‘stuff’ of nature. Thales (624-546 BCE) thought that this was water, Anaximander (610-546 BCE) a kind of ether out of which came the opposites of hot and cold, wet and dry, while Anaximenes (585-525 BCE) believed that it was air that became transformed into earth, clouds, water, fire, and wind. At Ephesus on today’s Turkish west coast Heraclitus (535-475 BCE) advanced the theory of the world as ordered but in a state of constant flux originating from and subsumed by fire. Anaxagoras (500-428 BCE) thought the universe was the result of an organising principle like a mind, which he called nous): this nous controlled the universe and its matter which consisted of many permanent elements. It was probably Anaxagoras who introduced philosophy to ancient Athens. Another famous theory from this region was the atomism of Leucippus (5th century BCE) and his pupil Democritus (460-370 BCE) who claimed that the world was comprised of an infinite number of minute, permanent and indivisible particles with different shapes called atoms. In space they collided to unite in various ways and form the objects of the universe – so change in the natural world was simply the rearrangement of eternal and unchanging basic units of matter.

But this mode of thinking was not confined to logic, mathematics and the nature of matter. Herodotus (c. 484–425 BCE) from Halicarnassus, a few miles south of Miletus, built on the work of his predecessor Hecateus (c.550–476 BCE) of Miletus by attempting to explain historical events in purely human terms, most notably the Persian invasions of Greece, and for this he has become known as ‘the father of history’.

Pythagoreans & Eleatics

From the southern Italian Eleatic School (named after the town of Elea, today’s Velia) came a doctrine of unity (monism), Xenophanes (570-470 BCE) postulating God as an omnipresent and eternal governing force in the world, while Parmenides (510-440 BCE) took an opposite view to Heraclitus considering the truth of the world to be permanent and unchanging and everything else mere appearance. In this he was supported by Zeno (490-430 BCE) famous for several challenging philosophical paradoxes. Sicily also produced philosophers like Empedocles (490-430 BCE) who believed that everything in the universe was the result of four basic and unchanging substances – earth, air, fire and water. These four ‘classical elements’ would be a part of later Greek philosophy and this idea continued through the Middle Ages. Empedocles also, with amazing accuracy, calculated the diameter of the earth.

The Pythagorean school at Croton (a town that was part of a Greek colony established on the southern Italian peninsula) was established by Pythagoras of Samos (582-496 BCE) who had fled his native island to escape persecution. He believed in the transmigration of souls: his followers were vegetarian, held all property in common and they studied a subjective and transcendental world of harmony, mostly through the medium of number and mathematics. Generations of students have laughed at the story of Pythagoras believing that the farting produced by the huge consumption of beans was the souls of dead men crying out, the same students also appreciating the beauty of his mathematics, his discovery of musical harmony resulting from the mathematical relationships of different lengths of vibrating string, and the famous Pythagoras’s theorem. Among the people he distantly influenced was the geometrician Euclid (fl. 300) who worked in Alexandria during the reign of Ptolemy I (323–283 BCE) but perhaps most significantly the philosopher Plato whose work shared the Pythagorean emphasis on mathematics, mysticism, politics as an Orphic tradition.

Orpheus, a legendary musician, poet, and prophet in ancient Greek religion and myth, was known to all as a mesmerising singer whose songs entranced nature itself. Pythagoras by studying the sound produced by different lengths of vibrating string was able to provide a mathematical explanation of the musical harmonies we find so pleasing to the ear and on which so much music is based, his calculations revealing the strange presence of mathematics within nature – the ‘harmony of the spheres’ – and revealing the way that the mathematics of harmony exists in a timeless way quite independent of human judgment and observation. The Orphics believed a spark of God dwelt in each human being and that this heavenly soul could pass from the prison or tomb of the body into divine infinity but only by living a life of purity and asceticism. Plato, deeply influenced by the Orphics, himself had a profound influence on the thinking of early Christian church fathers.

Over a 200 year span the Presocratic philosophers established the agenda for future western philosophy: the study of the basic stuff of the universe, its order and causal relations; the source of reliable knowledge – whether from the senses or reason; and the nature of the good life.  They also prepared the ground for the unfettered and brilliant thought of three men whose ideas are woven into the very fabric of western society – Socrates, Plato and Aristotle. We’ll first look at these men as people for examining their ideas.


Socrates lived in a period known as the Golden Age of Athens (c. 480-404 BCE) when the invading armies of Persia were defeated and the Greek Empire expanded, the resulting prosperity bringing intellectual and artistic achievement. He was dumpy and pugnacious. He chose to live a frugal life and daily, in the Agora (the market place in Athens) he challenged the accepted beliefs and self-interested preoccupations of Athenian society. His mind was preoccupied by elevated and controversial matters and, quite likely, his surly manner and obscure philosophical chatter would have been extremely irritating to people going about their daily lives. His constant stinging remarks earned him the title ‘Gadfly of Athens’ and these intellectual barbs eventually became too much for the authorities who condemned to death for ‘refusing to recognize the gods recognized by the state‘ and of ‘corrupting the youth of Athens‘. Death was by drinking hemlock (Conium maculatum).

Socrates bequeathed to the world the famous dictum ‘An unexamined life is not worth living‘. His devoted pupil, the 27-year-old Plato, was devastated by this turn of events and left Athens, probably spending time in Egypt studying in Alexandria with mathematicians, then joining the ascetic and vegetarian Pythagoreans in Sicily. But all the time he was wrestling with the idea bequeathed to him by Socrates ‘How am I to live; what does it mean to live a Good Life?‘.


we are told, was a handsome man born into a wealthy and influential Athenian aristocratic family: he excelled at sport and distinguished himself in battle. The name Plato was actually a nick-name meaning ‘flat’ or ‘wide’ and referred to his broad shoulders. Clearly an intelligent boy his family believed that he was ideally suited for political leadership. But to their annoyance he fell under the intellectual spell of the acerbic and portly Socrates who was of more lowly social origins having a father who was a sculptor-stonemason and mother a midwife.

After twelve years of travel and study Plato returned to Athens where he opened his famous philosophical school called the Academy located on the outskirts of the city – it was a forerunner of the modern university and a place of education that would flourish for over 900 years until closed for heresy by the Christian Roman Emperor Justinian in 525 CE (see Academy & Lyceum in article on Theophrastus).


(see also entry under Theophrastus)
Aristotle was a Macedonian and an aristocrat, the son of a royal physician and therefore known as an Asclepiad (Asclepios was the Greek god of medicine). Epicurus once called him a ‘drug-monger”.

Aristotle’s life and influence on zoology and science is beautifully described in Armand Leroi’s book The Lagoon (2014). Aristotle had tutored the young Alexander the Great, son of King Phillip of Macedon, before attending Plato’s Academy Aristotle was more down-to-earth than Plato, focusing less on the sublime and more on objects right here in the physical world.

Aristotle and his student Theophrastus (who followed Aristotle as Head of the Lyceum, the school of peripatetic philosophy in Athens) made a mutual pact to study the natural world together: Aristotle would study the animal kingdom and Theophrastus the plants. Together these two men established the foundations of modern biology, zoology, and botany. Not only did Aristotle question Plato’s famous transcendental world of ‘Ideas’ or ‘Forms’ (see the allegory of the cave, later) but he was also lean and dapper with an aristocratic bearing. Historical accounts say that he had skinny legs and piggy eyes and would preen himself, wearing rings, fussing about his hair and dressing very smartly in a neat and unphilosophical way, even speaking with a lisp.

Pre-Socratic natural philosophers were materialists who regarded nature as consisting only of matter (Earth, Air, Fire, and Water in various combinations). Aristotle criticised this view because matter is always changing. Any functional structure, like an organism, can have all or some of its matter replaced by different matter and yet retain its identity as a particular organism. That is, continuity of identity is maintained not through the matter of the organism but through the way matter is organised into functional structure. Matter is just ‘stuff’, when an organism grows it grows in a structured way, it does not simply get larger in the way that simple ‘stuff’ does.

Plato and Aristotle frequently and disparagingly referred to another school of philosophy, the Sophists. There were no fees at Plato’s Academy and Aristotle’s Lyceum but young men (or, more likely, their parents) would pay fees for tuition from the Sophists. Sophists were regarded as shallow educators of the day, charging aristocratic families exhorbitant fees to prepare their young men for public life in politics and the law courts by training them in public speaking and persuasive argument (rhetoric): the emphasis was on subjectivity and quick-wittedness rather than arguments of substance. Better known Sophists of these times included Protagoras (490-420 BCE), Gorgias (487-376 BCE) and Hippias (485-415 BCE).

Plato’s divided self

Plato was troubled by the lack of harmony in human existence, what we might call the ‘human condition’. In a world of confusion, conflict, disease, and deprivation, how are we to find happiness, harmony and contentment?

In his day, as now, religious movements provided people with solace and comfort in faith. Plato, however, wanted to engage in a full rational examination of the situation and its possible solutions. His philosophical investigations come down to us as books of dialectical debates between people of competing views.

His most famous work is The Republic, a monumental work of western culture. His clarity of thought and expression provided a compelling intellectual framework for thinking about human existence, his work containing philosophical, psychological, and political insights that are deeply entrenched in Western thinking to this day.

Plato believed that we all desire harmony and happiness, not just an inner peace or harmony but a social harmony as well: this is what he famously called ‘The ‘Good Life’.

He concluded, in general terms, that to achieve this harmony required a just person living in a just state. It was not sufficient for the individual to be just: Plato had seen what a corrupt society had done to his just friend Socrates. To establish a just society, Plato thought, required a universal, knowable and objective morality, a morality as self-evident to everyone as 2 + 2 = 4.

Being a philosopher Plato knew only too well that if he was to persuade other people to his views then he needed carefully considered explanations and precise definitions of exactly what he meant by the Good and the Just.

The Good

To establish his case Plato first had to demonstrate how we come to know anything at all, by making clear his views on what constitutes secure knowledge and how this is acquired. And to do this he had to make a clear distinction between what things seem to be (their appearance) and what they truly are (reality).


Plato borrowed his views on the fundamental nature of reality (what is now known as metaphysics) from two highly influential pre-Socratic philosophical traditions.

Philosophers had already noticed the paradox of permanance in change. We are all familiar with the saying ‘the more things change the more they are the same’. Today, for example, we know that every material part of our body changes every seven years, and yet we assume we are the same. What exactly is it that changes, and what is it that stays the same? And is it permanence or change that you think characterises what actually exists?

Pre-Socratic philosopher Heraclitus (c. 535 – c. 475 BCE) believed that the essence of existence is change. Heraclitus had famously stated that ‘different water flows over those who step into the same river twice‘ (you cannot step into the same river twice). He also claimed that ‘conflict is the father of everything’. Certainly the evidence of our senses suggests that the world is constantly changing.

This earthly state of constant flux Plato called the world of ‘Becoming‘.

In contrast Parmenides of the Eleatic School (fl. 5th century BCE) argued that the apparent world of change was a delusion. If we take a step back from the hurly-burly of life we realize that things actually never change, the constant change described by Heraclitus was a demonstration that, paradoxically, underlying this flux, things remained the same. Change was always superficial, he thought. Things did not come into and go out of existence, they persisted.[8] We might think of the physical laws of conservation of matter and energy here. Behind worldly activity, Parmenides’s believed, was a world of permanence, of eternal unchanging truth, a transcendental or spiritual world – and this Plato called the world of ‘Being‘.

These two Pre-Socratic thinkers expressed two profound differences in the way we observe and understand the very nature of everything: Heraclitus emphasised ‘becoming’ as difference, of many changing physical objects or particulars; Parmenides emphasised unity, permanence, sameness – a universal and eternal constancy.

Acknowledging both these points of view Plato’s metaphysics of existence (now known as ontology) was about both this earthly world, which is a world of change or Becoming, and a spiritual or transcendental eternal world, a world of ‘Being‘ which was the foundational stability that existed behind the superficial world of flux.


Having established his metaphysics Plato then examined our sources of knowledge (the study of knowledge is now known as epistemology) which, he believed, were of four kinds,[2] two in the world of Becoming and two in the world of Being.

In the earthly world of change or Becoming we obtain knowledge either from other people, or from our own personal experience. From other people come the beliefs of culture, tradition, and authority which, he was quick to point out, were notoriously unreliable. We can call this knowledge ‘conjecture’ but Plato was less generous, calling it ‘illusion’. For Plato the second source of knowledge in the world of Becoming was our sense experience which was clearly unreliable because our senses are both limited in extent and also easily deceived. His conclusion was that knowledge in the world of Becoming was at best unreliable and mostly just a matter of opinion, not universal and eternal truth: in fact the earthly world of Becoming was demonstrably imperfect.

So how can we possibly acquire the kind of certain or true knowledge that Plato needed to define Justice and the Good?

Plato believed that this came from the world of Being, and to explain this unlikely idea he drew on what he called ‘Forms’ (eidos). Forms, he claimed, exist independently of our minds. They are objective and not constrained by space and time: they are eternal, perfect, archetypal and essential. Above all they are intelligible to thought: they are like ideals or the essences of things.

In this earthly world, Plato claimed, we have in our minds the ‘idea’ of not only abstract things like justice, beauty, and truth but also of material things like trees, dogs, and the colour red. When we think of a ‘tree’ we do not necessarily think of a particular tree but of trees in general or ‘treeness’. ‘Treeness’ does not exist in this world but we can understand it, it makes sense as an idea, it is like the ‘essence of tree’ or even our verbal definition of trees in general – and this is what Plato called a Form. So, although we cannot experience the Forms directly in the physical world, as they are not physical entities, we can nevertheless understand them.

This is difficult to grasp. Forms are intelligible in the way that the truths of mathematics are intelligible and eternally true. A mathematician can understand how a point can have no extension and a line can have no width – even though when represented in this world they must have these properties. Mathematical points and lines are something we can only grasp with our minds. Similarly we can understand that 2 + 2 = 4 is true, and will always be true, even though it is an idea (Form) that has no physical existence in our world of Becoming. Think of the miraculously succinct precision of an equation like e = mc2 as it communicates to us a simple basic truth about the physical universe. Pythagoreans were deeply alarmed when they discovered irrational numbers because they presented a threat to the order they saw elsewhere in mathematics. Numbers, it appeared to them, were a part of existence independent of humans. Numbers existed in some sense before their discovery and would still exist, even if never discovered: their existence did not depend on either humans or the presence of a universe of space and time to house them.

The relationship between physics and mathematics remains an enigma as immaterial mathematical truths do not appear to be invented but discovered: in some strange way embedded – not in our minds, but in reality.

This then was the third kind of knowledge (we can call it ‘understanding’) which is an earthly indication of what actually exists in the world of Being. Plato insisted that the Forms were not some vague abstraction. This reality was mind-independent (transcendental) but it was nevertheless capable of precise definition, it could be grasped by the intellect and reason, and it could be applied in a practical way to human affairs in the same way that we can apply mathematics to practical problems. Philosophically this Platonic view is associated with a priori knowledge and the philosophical school of thought known as Rationalism which is contrasted with the a posteriori knowledge of Empiricism.

There was a further fourth way of accessing true knowledge and that was by direct experience of Forms in the world of Being. It is not clear exactly what Plato meant by this but he was probably referring to either the afterlife in eternity, or a mystical experience akin to the Nirvana of Buddhism. In this aspect of his philosophy Plato was expressing the mysticism common to religious and philosophical systems of his (and our) day across the world.

Forms for Plato were like shadows of things which actually exist in a perfect, eternal, changeless and absolute world. The ‘Form of all Forms’, which included morality, Plato believed was the Good and the Good, like the Sun, gave light to everything. Plato’s separate world of Forms was not like a heaven inhabited by spiritual beings but a world of abstract general facts. The philosophy of mathematics illustrates well the dizzying world of the existence of generality. We can dismiss number as a mental construct but it merges so seamlessly, practically, and economically with science and the physical world that it cannot possibly be an imaginative fantasy. And yet, how can number actually exist in any way beyond our minds?

Plato’s claim for a transcendental realm of Forms (universals) has occupied philosophers to this day as they struggle with the existence, causal powers, and location of abstract objects.[7]

Allegory of the cave

These thoughts, Plato realised, were difficult to grasp and so, in Book 7 of The Republic, he illustrated what he was trying to say by means of his famous allegory of the cave.

He asked readers to imagine themselves as prisoners tied up facing a wall in a cave having experienced nothing else. Behind these prisoners, and unseen by them, are people around a fire. The voices and flickering shadows on the wall in front of the prisoners are then understood by the prisoners as real, the shadows being living objects with voices. This, Plato said, was like the world of conjecture or illusion. One prisoner escapes from his bonds and sees the people, the fire, and the shadows. Though at first unbelieving, he eventually understands how the shadows seemed real. This, Plato said, is like the world of experience. Then the prisoner discovers the entrance to the cave, breaking out into a miraculous world of light and colour. At first the brightness is too great and he is tempted to return to the cave. But after a while his eyes adjust and he can see the trees, rivers, and mountains. This, Plato said, was like the world of Forms. Eventually the prisoner realises that he can only see the trees, rivers and mountains because of the light from the Sun which is so dazzling that he cannot look at it directly. The Sun, Plato said, which governs the seasons and all life, was like the Form of all Forms, the root of all Being, it is what gives meaning to the Forms: it is the Good.

Plato makes several further general observations. Things in the cave are mostly human, or human constructs, but outside the cave is the natural world in all its splendour. Knowledge is not easy to gain but is painful, people prefering the comfort and reassurance of the cave. Initially we resist the glare of knowledge and cannot be forced towards it. But once we have experienced it and appreciated its wonder we must then confront the moral question as to whether we go back into the cave to enlighten those we have left behind. Plato, remembering Socrates, was skeptical about human reactions. He noted that if you return to the cave with your knowledge, trying to convince people that there is a better world outside, then you will probably be misunderstood and ridiculed. You could even be killed. People do not want to be told that they are living in a world of illusion: they do not want to be enlightened.

Plato insisted that anyone destined for public life must have strived for justice and truth through the use of their reason: they must have at least glimpsed the Forms that are shadows of the Good. For Plato this meant a selective education system, the philosopher-kings or guardians. This was a powerful idea that was to dominate western education for many years, restricting social mobility and demarcating a clear social hierarchy.

The Just

Having now defined true knowledge, the Good, Plato then asks how it is possible for us to live in harmony with ourselves and society.

The Just person

To become Just or ‘harmonious’ Plato believed that we must reconcile three competing aspects of our mind (or ‘soul’ as he called it). These key elements were reason (logos),[7] will or spirit (thumos), and appetite (epithumos). Reason could be satisfied by wisdom and logic, spirit satisfied by honour and courage, and appetite or desire satisfied by temperance and moderation. However, overall harmony could only be achieved when logos prevailed over the other elements, like a charioteer controlling his horses.

Just or harmonious person was therefore one whose reason maintained a balance between the virtues of wisdom, courage, and temperance (this has parallels with Buddhist philosophy).

The Just society

Plato made an analogy between the individual and society. Although reason must always prevail, people in society will inevitably show preferences for particular virtues. Some are driven more by honour and courage, others by desire. This could be accommodated through their occupations, fitting their occupation to their natural inclinations. Those governed mostly by reason (those who had seen the Good) were suited to become the philosopher-rulers or guardians (reason) and they should carefully manage both the soldiers (spirit & honour) and also the merchants, tradesmen, and citizenry (appetite). In so-doing they were fulfilling three vital functions: government, security and protection, and nourishment. When all these factors are in balance then we have a Just, well-governed city-state.

So, Plato concluded, morality (the Good) was absolute, objective and knowable through the use of reason and logic. For both individuals and society to flourish and be harmonious (the Just individual in the Just society) reflective judgment (reason) must guide the will, intuition and appetite as people endeavour to put into practice the four cardinal virtues of wisdom, courage, moderation, and justice.

Aristotle’s views

Aristotle, though accepting the primacy of reason in all things, did not accept Plato’s theory of Forms.

Like Plato he believed there was a pure idea defining things, a kind of ‘essence’ but this existed in objects and things themselves, not in some ethereal other-world (his view became known as essentialism). Concepts like ‘tree’ and ‘red’ were not things that could exist outside space and time, they were common properties shared by real objects. Such an understanding brought Plato’s transcendentalism down to earth and is the main reason why Aristotle has often been regarded as the first true scientist. Although making major contributions to philosophy he was also deeply concerned with the physical world and especially biology.

For Plato the soul (psyche) was that part of us that reasons, governs our existence, is the source of moral virtue, a kind of life force that persists after death. This is the sense of ‘soul’ that has carried through to us today. Plato also identified a ‘world soul’ (Latin anima).

Continuous with the beliefs of prehistory the world for the ancient Greeks was a place of ‘vitality’ – its contents imbued with all kinds of ‘powers’ (properties) and full of endless activity that was not chaotic but ordered. Our perception of the world is as a mostly dead place following the blind and purposeless laws of nature. For the Greeks the world order like ‘organic’ order that had both direction and purpose: this was the universal ‘nous’, not blind and purposeless but following a path of cosmic reason.

Aristotle devoted an entire book De Anima (anima is Latin for mind or soul) to his reflections on psyche. Though difficult to pin down, Aristotle’s ‘soul’ was not like a spirit inhabiting the body. For him the soul was what animates and defines an organism as its Form (eidos): a disembodied soul, for Aristotle, does not make sense. Soul includes both potentiality (dynamei) and actuality (entelecheia) as part of the organic world of change. By ‘potentiality’ we might understand an organism’s inherent nature or genetic make-up (how an acorn carries within it the potential to become an oak tree) . . . along with the capacity to perpetuate likeness in the continuity of the species. But the soul is also the organism’s ‘actuality’: that which generates its organic change in its daily functioning through nutrition, motion, growth, ageing, sensation and all those processes that enable survival and reproduction including, in conscious organisms, emotion, the will and intellect. Aristotle’s soul was like a life principle or principle of unity.

The soul for Aristotle included an organism’s eidos and its final cause which was . . . its goal, purpose, or meaning . . . and the reason for its existence. The final cause entailed his three other causes. And his analysis still makes sense in a world without disembodied spirit. However, it has been largely rejected by modern science through a distrust of the idea of final cause (but see the article Purpose).

So, for Aristotle living things differ from non-living by the possession of a soul, or principle of life. In De Anima he tries to give a general definition or diagnosis of life (its essence), an account of biological organization (self-organization) that we see in living organisms, and a discussion of the factors that make one kind of organism different from another. Much can be lost or confused in translation and interpretation of the ancient texts. We must remember that today we are born into a world of established fact that seems both simple and obvious. Aristotle was trying to establish first principles with little prior knowledge to build on, and he made an admirable attempt.

These two philosophers, Plato and Aristotle, represent the competing traditions of transcendentalism (Plato) and science (Aristotle).

Plato was an idealist who saw the world of particulars, the objects of our daily existence, as part of a world of change and becoming: they are fleeting copies of Forms that existed in an eternal realm that lies outside space and time. This was Plato’s metaphysics, his real world. For Aristotle particulars were the primary realities. Particulars were not ‘becomings’ but ‘beings’. They still had ‘form’ but this was imminent, contained within, matter. Particulars were thus hylomorphic, consisting of both matter and form, and it was never possible for form to exist independently. In this sense Aristotle was a physical realist.

For Aristotle the ‘good life’ was a full life that, under the rule of reason, maximized the actualization of individual and collective potential to achieve human happiness and wellbeing.

Both of them left their mark on Christianity and Islam. Plato’s ideas persisted through the theology of the Middle Ages in the work of St Augustine, the Augustinian monks and Franciscans, while Aristotle (known in medieval texts as ‘The Philosopher’) continued his influence through the work of St Thomas Aquinas and the Dominicans (Jesuits).

The Orphic elements of Plato’s philosophy – its religious, spiritual, and priestly tone, its concern with immortality, mysticism, transcendence and other-worldliness, and his deep respect for mathematics – was probably derived from the Pythagoreans.

We remember Aristotle for his academic precision. English philosopher Bertrand Russell speaks of him as follows:


‘ . . . after his death it was two thousand years before the world produced any philosopher who could be regarded as approximately his equal . . . he is the first to write like a professor: his treatises are systematic … he is a professional teacher not an inspired prophet . . . his work is critical, careful, pedestrian, without any trace of Bacchic enthusiasm . . . the errors of his predecessors were the glorious errors of youth attempting the impossible; his errors are those of age which cannot free itself of habitual prejudices’.[5]Aristotle is the last Greek philosopher who faces the world cheerfully; after him, all have, in one form or another, a philosophy of retreat‘.[6]


Aristotle worked on his own philosophical ideas in the Lyceum in Athens. Like Plato he had no doubt that reason should be paramount in life and, in particular, it should be used to overcome bad habits and the unsavoury aspects of our human nature. Happiness, Aristotle believed, could only be achieved by cultivating desired behaviour, what the ancient Greeks called the virtues (arete, sometimes translated as excellence). Strengthening the virtues was not straightforward, it required constant attention and hard work, but it could be improved and became easier through habit: it therefore needed to be a major part of the education process.

These ideas as expressed by Aristotle in his Nicomachean Ethics make powerful sense today – but they have lost currency through being abused historically, especially in the Victorian era, by the authoritarian imposition of mindless rule-following and corporal punishment both within the family and school, resulting in predictable rebellion.

X-Ray image of a stingray

loctrizzle – Accessed 25 May 2017
Most people know of Aristotle through his masterful works on logic, ethics, and politics. But for biologists there are nine books that he wrote about animals, many of which he had personally studied in the field – dissecting, examining and speculating on the function of the various parts. This work of experiment and observation flies in the face of the claim that true science only began in the modern era. He classified organisms in a nested hierarchy that reflected, unbeknown to him, evolutionary descent with modification. Linnaeus, the great eighteenth century Swedish ‘Father of taxonomy’ took on board the Platonic and Aristotelian legacy of species (eidos) and genus (genos). Aristotle’s down-to-earth biological work was pioneering as he effectively founded the discipline of zoology at a time when mathematics and astronomy reigned supreme:

‘It is not good enough to study the stars no matter how perfect they may be. Rather we must also study the humblest creatures even if they seem repugnant to us. And that is because all animals have something of the good, something of the divine, something of the beautiful’ . . . ‘inherent in each of them there is something natural and beautiful. Nothing is accidental in the works of nature: everything is, absolutely, for the sake of something else. The purpose for which each has come together, or come into being, deserves its place among what is beautiful’
Aristotle – De Partibus Animalium (The Parts of Animals) – 645 a15


Aristotle’s sentiments are aptly referred to as ‘The Invitation to Biology’.


Famous ancient Greek thinkers


fl. c. 700 – Homer

Archaic Period – 800-500

800-200 – Axial Age

fl. c. 750 and 650 – Hesiod
624-546 – Thales
610-546 – Anaximander
585-525 – Anaximenes
582-496 – Pythagoras
570-470 – Xenophanes
510-440 – Parmenides
c. 510 – c. 428 – Anaxagoras
535-475 – Heraclitus

Classical (Hellenic) Period – 500-350

490-430 – Zeno
490-430 – Empedocles
490-420 – Protagoras
487-376 – Gorgias
485-415 – Hippias
c. 450 – Leucippus
460-370 – Democritus
469-399 – Socrates
c. 427 or 423-348 – Plato
384-322 – Aristotle
356–323 – Alexander the Great (Alexander III of Macedon)

Hellenic Period – 320-30

341–270 – Epicurus
c. 300 – Euclid


354-43 – St Augustine
525 – Lyceum closed by Emperor Justinian
1225-1274 – St Thomas Aquinas


The intellectual world of the ancient Greeks, as exemplified by our five great thinkers Socrates, Plato, Aristotle, Theophrastus and Epicurus was later adapted by the more practical Roman society which admired Greek culture completing, rather than destroying, many of the unfinished Greek monuments and, through its empire, laying the foundations for European society, its colonies, and eventually Western society as a whole (see Ancient Greece).

European leaders-to-be were for many generations educated in the classics, the literature, science, philosophy and ethos of the classical world. Europe inherited from the Greeks and later Romans not only a tradition of intellectual rigour but their system of economy, justice, and politics, even social attitudes ‘warts an’ all’ concerning the role of women and sexuality, education, the structure of society, and sport.  

These men are Greek representatives of a stream of intellectual exploration that was taking place across Afro-Eurasia during the Axial Age (c. 800-200 BCE). In an unprecedented period of introspection the known world was taking mental stock in a movement that included not only the Mediterranean philosophers and developing Abrahamic religions but, in China, Taoism and Confucianism, in India Buddhism, and in Persia Zoroastrianism.[3] Cosmopolitanism had brought a questioning of the authoritarian beliefs and inflexibility so often associated with small isolated groups (see History in 10,000 words).

In The Republic and Timaeus Plato constructed an intricate and compelling edifice of thought, a toolbox for understanding and coping with the world, his intellectual architecture being something that could be further worked by subsequent generations. Much of the foundation of Western science came to us through ancient Greek thinking and Plato especially would provide the bedrock of all subsequent Western philosophy including those aspects of his thought incorporated into Christianity by St Augustine. We may not agree with his overall thesis today but the clarity, depth and breadth of thought expressed in The Republic over 2000 years ago is truly stunning: it laid out a roadmap for philosophical debate that has continued to this day with its carefully crafted metaphysics, epistemology, ontology, ethics, political theory, and theory of education. It even included a mystical four-step path to transcendental enlightenment.

Plato was a Rationalist. His metaphysics claimed that the ultimate reality was the world of Being, the world of Forms, which could not be accessed through the senses, but only through the intellect using reason and logic. He is also associated with what became known as ‘idealism’, maintaining that ‘truth’ was abstract and transcendental (like the truths of mathematics, and the idea of the Forms) existing more clearly in our minds than in the natural world and only insofar as it approximated the ‘idea of the Good’. The world of sense experience was unreliable and illusory. It would take the genius of Aristotle to provide an alternative more earthly and scientific outlook in which objects were more real than forms.

Saint Augustine (354-430 CE) in a school of thought that later became known as Neoplatonism, translated Plato’s worlds of Being and Becoming into the worlds of Heaven and Earth and the Form of the Good into God. Following the decline of the Roman Empire and the rise of Christianity Plato’s works would be lost to the West until recovered by Italian Renaissance humanist Petrarch in the fourteenth century. Christian medieval scholastic theologians subsequently transposed Plato’s ideas into Christianity aligning them with the world of Christian revelation. Plato’s ‘soul’ (his tripartite mind) also belonged to the world of Forms because though invisible and capable of self-reflection it ruled the body. As ideas are not physical things they must belong to a spiritual realm which, being eternal and unchanging, is more real than the transient material realm. As Forms were immutable then the soul too must be immortal, passing from the world of Becoming into the world of Being at death. For St Augustine Plato’s eternal world of Being, or heaven, was the place in the afterlife supporting the immortality of the soul. Plato’s objective morality became God’s law. Following Plato’s conviction that the world of sense-experience was unreliable, Christianity portrayed the physical world of experience as an inferior, imperfect or ‘fallen’ world, a wretched place totally unlike the perfect, eternal and transcendental world of God. This other-worldliness described by Plato in Phaedon, Timaeus and Symposium became known as Platonic idealism. Similar other-worldly analogies occur in Islam and Judaism.

Plato’s works remained available after the fall of Rome but underwent a major revival in the Italian Renaissance when in 1462 Marcilio Ficino (1433-1499), a catholic scholar and humanist, was appointed Head of a Platonic Academy in Florence modelled on the former Academy in Athens. Ficino was the first to translate Plato’s works into Latin; his attempts to reconcile Platonism and Christianity had a great influence on later philosophy although the Academy lasted only a few decades, being dissolved in 1492.

While all of Plato’s works survived, of Aristotle’s 150 works only 25-30 survive and these too were temporarily lost. Transcribed into Arabic by Islamic scholars Aristotle’s cogitations were later recovered by Christians during the Crusades, the depth of Aristotle’s thought being immediately recognised. Early Christian thinkers maintained that the application of reason to human affairs had resulted in a rag-bag of different viewpoints on all aspects of life resulting in chaos and confusion. Only faith could provide truth, certainty and support in life. Reason was condemned.

When Aristotle’s works were returned to the West they too were reconciled with the gospels through the ‘scholasticism’ of St Thomas Aquinas (1225 – 1274 CE) and his monumental work Summa Theologica that would become so influential in Christianity. Aquinas pointed out that God created not only the natural world but also the human faculty of reason which should not be denied a central role in life. With St Thomas Aquinas reason was once again permitted a place in intellectual life, Aquinas supporting his position by pointing out that reason could be used to discover and celebrate the order and wonder of God’s Creation (a view that became known as ‘natural theology’). Only through Aquinas’s admission of reason did science become acceptable within that early Christian world. Christianity then incorporated Aristotelian ideas (he was known as ‘The Philosopher’) like his teleology, into the Christian idea of God’s purpose or plan.

For both Plato and Aristotle existence entailed a plan and therefore a supernatural agency. Plato thought that the order we see around us in the universe must have an ‘organising principle’ or demiurge. Aristotle also saw purpose and design in everything around him and referred to this as telos (see Meaning & purpose) with God the prime mover or initiator of the universe but indifferent to human affairs rather than anthropomorphically caring for the universe in a paternalistic way.

Though acknowledging a spiritual world, Aristotle is most closely associated with ‘analytic empiricism’ which maintained that it was possible to obtain true statements about the natural world by means of careful observation and analysis (break-down and classification) combined with the use of rigorous logic. He did not share Plato’s disdain for the material world.

A scientifically-based bitter resentment of Plato for his transcendental religiosity, philosophical idealism and subjectivity, and authoritarian politics is not helpful as I hope you agree. Plato’s thought was modelled on mathematics and the physical mathematics of astronomy which looked upwards to the perfection and geometry of the heavens while Aristotle’s influence lay more in biology and society. Without Plato we would have missed so many insights and almost certainly not have had the benefit of Aristotle’s thought as their influence continued forward in the great traditions of Rationalism and Empiricism.

After the ancient Greeks open-minded philosophy would not return to the West for about 1200 years until the Renaissance when the intellectual battle-lines were clearly drawn. There were those following the transcendental Platonic tradition of innate ideas (the Rationalists) and those who followed Aristotle’s tradition of earthly observation (the Empiricists). These two schools of thought arrived at a stale-mate. Rationalists needed to generate objective truths from ideas untainted by experience that is, from a priori ideas), and this was a tall order. Meanwhile empiricists like John Locke and David Hume, who maintained that all meaningful ideas must be traced back to experience, had to confront the subjectivity of sense-experience, the ‘egocentric predicament’, an equally difficult problem. Only with Immanuel Kant would come the suggestion that our brain structures, or filters, our sensory input and that this is why we perceive the world the way we do – this filter was the a priori aspect of our ideas: it was a fusion of the Rational and Empirical positions. Philosophy could move on.

Now we can now see how Socrates, Plato, Aristotle and the other ancient Greek philosophers had a profound influence on the future character of subsequent religion, education, poetry, literature, the theatre, science, politics, law, economics, society, morality, sexuality, sport and much more. Their influence on the history of ideas cannot be doubted, they are at the heart of the Western grand narrative. No education is complete without a knowledge of their contribution to the modern world and plant people will hold a special place for Theophrastus, Aristotle’s heir at the Lyceum who laid the foundations of plant science. In our admiration and deep respect for their intellectual rigour we should not forget our social differences – these men lived in a strongly hierarchical society that supported a privileged aristocracy and slavery, and denied women political and legal rights, Aristotle even describing women as ‘incomplete men’.

This was a cosmopolitan and divided society of extreme rivalry and competition that strived ruthlessly for excellence in all fields. Historian Hesiod spoke of ‘good strife and bad strife’, distinguishing between the noble emulation of healthy and peaceful competition that can benefit all, and the malicious and destructive competition of warfare. We now see ancient Greece as a society of contradictions. Daily life was steeped in religion and ritual observance but Greece gave us spiritual skeptics and natural science. Great men like Pericles and Alexander were admired almost to the point of worship as gods while at the same time there was the strong egalitarianism we associate with democracy. And yet the democracy we attribute to the Greeks existed in a hierarchical society with an aristocratic and wealthy elite. The physical magnificence of Greek monuments, their engineering, and the many benefits of cosmopolian trade that marked a great civilization were only achieved through the use of slave labour. The ultimate measure of a Greek man (women hardly counted) was his demonstration of courage, loyalty, and heroism in warfare. Little wonder that ‘why?’ had such a privileged position in the Greek world. In the search to ‘Know themselves’ they lived life (and death) to the full, stretching intellectual and physical experience to its limit, challenging future generations to do better. Roman military might would eventually prevail but Greek culture was respected and preserved.

Modern study of the Axial Age has tempered the former grip of the Greeks and ancient Mediterranean societies over the Western mind suggesting an exaggerated and eurocentric interpretation of their role in world history. Perhaps the influence of the classics within academia is still overstated in a world that becomes more global by the day . . .  but Greco-Roman influence on the old British empire cannot be doubted and this influence is strong and continuing.

In a debate between now British Prime Minister Boris Johnson and Cambridge Professor Mary Beard on the relative merits of ancient Greece and Rome, Johnson pointed out how, even though nearly 2500 years old, many ancient Greek works of literature, art and philosophy are  ‘imperishable masterpieces’. Greek mythology can be seen today to contain penetrating psychological insights, while Greek literature and art explored new ideas as never before . . . the list goes on. 

The vital link between human nature, reason, morality, science, and sustainability will be explored in the other articles of this section.

Key points

  • Ancient Greek thoughts, as exemplified by the five great thinkers Socrates, Plato, Aristotle, Theophrastus and Epicurus was later adapted by the more practical Roman society which, through its empire, laid the foundations for European society, its colonies, and eventually Western society as a whole
  • The analytic often non-religious thought called natural science that we associate with the five great Greek philosophers was grounded in the work of pre-Socratic philsosophers (physiologoi) in the Greek colonies on the present-day coast of western Turkey (Anatolia), mostly at Miletus and Ephesus, and other communities of coastal southern Italy (known to the Romans as Magna Graeca) such as the famous Pythagorean school. No doubt many of their ideas went back further to the early civilizations in Egypt and Mesopotamia
  • For many years, study of ancient Greece and Rome formed the core of the Western education system known as the ‘classics’.  European leaders were, for many generations, educated in in this tradition which influenced western literature, science, and philosophy. The ethos of the classical world can be felt today through its historical influence on science medicine, astronomy, mathematics, logic, engineering, ethics politics, law, architecture, sculpture, literature, oainting and much more
  • Plato believed in a transcendental or subjective world independent of the material world, a world of ideas or Forms (eidos), what later became known as Platonic Idealism. His ideas would be united with those of Christianity by Medieval theologian St Augustine and later by Florentine Marsilio Ficino who translated his works into Latin at the Platonic Academy in Florence. Plato’s careful reasoning produced a roadmap for philosophical debate that has continued to this day including a carefully crafted metaphysics, epistemology, ontology, ethics, political theory, and theory of education. It even included a mystical four-step path to transcendental enlightenment.
  • Aristotle used the term Form in a non-supernatural way to mean that character of living organisms, the life principle that animates them possessing both ‘potentiality’ (today we might call this the genetic make-up) but also ‘actuality’ or changing functionality through nutrition, motion, growth, ageing, sensation and all those processes that enable survival and reproduction including, in conscious organisms, emotion, the will and intellect (nous). This was all directed at what he called the ‘final cause’ of the organism … its goal, purpose, or meaning … the reason for its existence. His thinking would be incorporated into Christianity by the Medieval theologian St Thomas Aquinas
  • Aristotle is often said to be the first true scientist. For biologists it is not his ethics, logic and politics that attracts so much as his ‘Invitation to Biology’
    • These ancient Greek thinkers did much of the original hard mental work needed to provide a coherent framework for existence – work that nowadays we take completely for granted
    Marble, Roman artwork (1st century), Possibly a copy of a lost Greek bronze statue made by Lysippos.
    Courtesy Wikimedia Commons

    Luni marble copy of a portrait made by Silanion ca. 370 BC for the Academy in Athens
    Courtesy Wikimedia Commons
    Marble, Roman copy of a Greek bronze original by Lysippos from 330 BCE; the alabaster mantle is a modern addition
    Courtesy Wikimedia Commons
    Media gallery
    The three videos below cover the material discussed here, and are an interesting contrast in presentation styles. Do you like serious-academic or jokey-matey? All the presentations are packed with information.

    The Presocratics: Crash Course History of Science

    CrashCourse – 2018 – 12:31

    Plato and Aristotle: Crash Course History of Science

    CrashCourse – 2018 – 12:28

    Socrates, Plato, and Aristotle

    Lectures Beyond Beyond – 2015 – 24:13


    First published on the internet – 1 March 2019

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