There are some questions that science cannot answer. What kind of person ought I to be? Is there a God? How dependable are my beliefs? Am I more than just a physical body? Questions such as these are the subject matter of philosophy. Its tools are curiosity, open-mindedness and reasoned argument. Modern philosophers use a large technical vocabulary and complex methods of analysis, but its roots go deep into ancient history. Philosophy began with Thales of Miletus, who predicted an eclipse of the sun in 585BC (although some claim that he merely observed it). Thales wanted to understand how the world works. He wasn’t content with mythological and supernatural explanations. After meticulous observation and careful thought, he concluded that “everything is water” and that magnets have souls.

In the following 100 years, a succession of thinkers struggled to make sense of the natural world. Men like Pythagoras, Heraclitus, Parmenides and Democritus shared the conviction that the world is ordered and intelligible and that by careful enquiry they could uncover its secrets. They became known as “philosophers”, from the Greek philosophia (love of wisdom), and were interested mostly in scientific problems.

In the 5th century BC, Socrates, a citizen of Athens, took philosophy in a new direction. He applied the method of critical enquiry to questions about man and his place in society, thereby laying the foundations of ethics.

Socrates was executed in 399 BC, but one of his pupils, Plato, constructed an elaborate and wide-ranging philosophical system. He argued for the existence of a timeless, unchanging world of “Ideas” - a realm of truth, beauty and ultimate reality.

Plato’s finest pupil, Aristotle, occupied himself with what can be seen, heard, smelled, tasted and felt. He organised and classified the various sciences, examined the logical structure of arguments and formulated influential theories of politics, ethics and metaphysics.

Socrates, Plato and Aristotle are the great Classical philosophers. Their ideas have exerted an unparalleled influence on Western society. Various philosophical schools followed them: the Epicureans pursued pleasure; the Stoics resigned themselves to fate; the Cynics rejected civilised values; and the Skeptics refused to believe in anything. The last great movement in ancient philosophy originated in the 3rd century AD with Plotinus. He took Plato’s ideas, added a liberal dose of mysticism, and concocted a philosophy (now termed Neo-Platonism) which for a time rivalled Christianity.

Ancient philosophy came to an end in AD 529 when the Christian Emperor Justinian outlawed its “pagan” teachings. However, it had already gained a permanent foothold in Christian theology thanks to St Augustine (354-430), who was strongly influenced by Neo-Platonism. Philosophy’s influence was still apparent 1,000 years later, when Pope Julius II commissioned Raphael to paint “The School of Athens”, which portrays many leading lights of ancient philosophy.

Don’t eat beans: Pythagoras

Pythagoras is one of ancient philosophy’s most enigmatic figures. He can be seen at the front left of Raphael’s painting, writing in a book. He was born on the Greek island of Samos, and moved to Italy when he was about 30.

There he founded a sect dedicated to a strict way of life and the pursuit of esoteric knowledge.

Pythagoras was a curious mixture of scientist, mathematician, mystic and madman. He believed in the transmigration of souls and claimed to remember his own past lives. He formulated bizarre rules for the purification of the soul: don’t eat beans, don’t break bread, don’t pick up fallen objects. A number of mathematical discoveries have been falsely credited to him, most famously the theorem concerning the sides of a right-angled triangle (it was known hundreds of years before by the Chinese and Babylonians, but Pythagoras and his followers proved it was right for all triangles). He believed in the mystical power of numbers, and taught that nature’s laws have a mathematical basis. Centuries later, this insight inspired Kepler and Galileo, who pioneered modern scientific method.

“We are and we are not”: Heraclitus

The solitary, brooding figure at the centre-front of the picture represents Heraclitus (c500 BC), a citizen of Ephesus in Asia Minor. Heraclitus wrote just one book, which is notoriously difficult and obscure. After reading it, Socrates reportedly commented: “What I understand is splendid; and so too, I’m sure, is what I don’t understand.” According to Heraclitus, the world is in a constant state of flux. “We step and do not step into the same rivers, we are and we are not,” he said. He identified fire as nature’s basic element - an unstable substance to account for a constantly changing universe. He had a contemptuous attitude towards his fellow men, regarding most as unthinking fools. His misanthropy led to his early death from dropsy after removing himself from society and living on grass and plants.

“Expert” opinions: Socrates

Socrates (470-399 BC) adopted the peculiar practice of standing in the marketplace in Athens, engaging passers-by in debate. A favourite ploy was to ask an acknowledged expert for his opinion on some matter. By skilful questioning, he would demonstrate that the “expert” did not know so much after all - for example, an army general could give no satisfactory definition of courage, and a religious zealot no coherent account of what pleases God. He was motivated by a desire for knowledge, believing that knowledge only emerges through a process of dialogue and systematic questioning.

Socrates switched the emphasis of philosophy from science to ethics. He taught that actions depend on opinions, and that each individual must take intellectual responsibility for forming those opinions. These notions proved unpopular with Athens’ leaders, who preferred people to take their moral cues from the State. He was put on trial, found guilty of introducing new gods and corrupting the youth, and sentenced to death. Refusing to plead for leniency or to attempt escape, Socrates submitted to the death penalty by drinking hemlock, surrounded by friends and admirers. The calm and dignified manner of his death has inspired many works of art. His legacy includes the Socratic method, a way of teaching in which skilful questioning is used to enable pupils to arrive at concepts for themselves.

Socrates can be seen towards the left of the picture, enumerating points on his fingers as he talks with Alexander the Great.

Platos’s other world

Plato (c 428-347 BC) was a devoted pupil of Socrates, but did not share his intellectual modesty. Socrates said: “Wisest is he who knows he does not know.” But Plato believed that the wisest can achieve knowledge. Influenced by Heraclitus’ belief that the world is in constant flux, he argued that we cannot have perfect knowledge of that which is constantly changing.

But Plato also believed in the existence of another world, a timeless, unchanging world of “Forms”, or “Ideas”, where everyday objects such as tables and horses are inferior copies of heavenly originals, or Forms.

There are also Forms of abstract items; these are not just intellectual constructs - they are more real than physical objects. According to Plato, the true philosopher can penetrate beyond the sensory world of “appearances” into the realm of Forms, and grasp the real essences of Truth, Beauty and Justice. Since only philosophers understand these things, it follows that only philosophers are fit to rule the State. The rest of us must be content to follow their orders and obey their laws.

Plato’s ideas may seem odd, but his genius and influence are beyond question. In The Republic, he raised almost every philosophical question there is, and established the philosophical curriculum right up to the present day. This prompted the British philosopher AN Whitehead to claim that the whole of Western thought “consists of a series of footnotes to Plato”.

In Raphael’s painting, Plato takes centre-stage, deep in discussion with Aristotle. He is pointing upwards to the world of Ideas, but Aristotle gestures downward towards the observable world.

Lifestyle of a Cynic

The School of Cynics was founded by Antisthenes c400 BC. He believed that true and lasting happiness is only to be found in a life of freedom and self-sufficiency. The Cynics despised worldly goods and rejected the conventions of civilised society. Their most celebrated member, Diogenes (404-323 BC), lived in a barrel, ate scraps, masturbated in the street and wrote approvingly of cannibalism and incest. Plato dubbed him “Socrates gone mad.” This primitive lifestyle earned him and his followers the name Cynics, meaning dog-like. Diogenes died after eating raw octopus in an attempt to show that cooking is unnecessary. He is shown in the foreground of Raphael’s painting, sprawled across the steps wearing a dishevelled blue cloak.

Aristotle: father of logic

Aristotle (384-322 BC) was born in Stagira in Macedonia. He enrolled in Plato’s Academy in Athens. He was enormously talented, and opened his own school, the Lyceum, following Plato’s death. Rejecting Plato’s abstract theory of “Forms”, he based his own philosophy on observation and empirical evidence. He organised and classified the sciences, invented logic (the study of valid reasoning and argument), and wrote on a wide variety of subjects, including politics, ethics, metaphysics, aesthetics and literary criticism. Following the death of Alexander the Great in 323BC, anti-Macedonian feeling spread through Athens, and Aristotle, who had once tutored Alexander, found himself under a trumped-up charge of impiety. He fled to Chalcis, where he died a year later, aged 62.

Aristotle is the most influential of all ancient philosophers: today’s academic disciplines are organised into categories that he invented; his tests to determine the validity of arguments are still used; his political writings contributed greatly to the concept of democratic government; and much else besides.

Garden philosophy

Epicurus (341-270 BC) is at the far left of the painting, wearing a crown of vine leaves. He taught that pleasure is the highest good, but some pleasures prove harmful in the long run. Advocating a modest lifestyle, he and his followers lived in a self-sufficient community, and were known as the “garden philosophers”.

Epicurus believed that much human misery is caused by fear of the gods and the fear of death. He came up with ingenious arguments to show that these fears are unfounded. For example, he wrote that “DeathI is nothing to us, since while we exist, death is not present, and whenever death is present, we do not exist”.

His agnostic tendencies and non-conformist lifestyle raised the hackles of some of his contemporaries, who accused him of sponsoring secret orgies.

Centuries later, the poet Dante consigned him to the sixth circle of hell for denying the immortality of the soul. A much altered form of Epicureanism exists today. Its adherents are committed to a life of sensual pleasure, and are often associated with liberal attitudes towards sex.

Present-day scientific disciplines all began as branches of philosophy. But modern philosophy limits itself to abstract questions that cannot be answered by empirical science. Definitive answers may never be found but perhaps, as Bertrand Russell maintained, the questions themselves are what is important: “Ithese questions enlarge our conception of what is possible, enrich our intellectual imagination, and diminish the dogmatic assurance which closes the mind against speculation.” Philosophy will not teach you what to think, but it will teach you how to think.

Gary Hayden teaches in Cheshire