Pre-Socratic Philosophy

The history of Western philosophy, although technically incorrect, begins with Socrates and Plato, not because the Platonic dialogues were the most significant philosophical texts to have been written in antiquity, but because they represent the earliest comprehensive philosophical treatises in recorded history. Pre-Socratic philosophy, however, is the true origin of Western philosophy.

Pre-Socratic philosophy is an umbrella term used to designate all philosophy – understood to mean rational, as opposed to mythological, theories and explanations – prior to the time of Socrates (469-399 BCE).

This designation and classification is both necessary and justified, not on account of a common theme or shared purpose amongst the Pre-Socratic philosophers, but due to the lack of direct historical resources.

The distinguishing characteristic of Pre-Socratic philosophy is the lack of a comprehensive treatise in which the views, theories and notions of these early thinkers, penned by their own hand, were recorded for posterity, for no such text survived the ages.

Therefore, Pre-Socratic philosophy is reconstructed from secondary sources whose works endured, such as later philosophers and historians, most notable among whom are Diogenes Laertius and Aristotle.

As such, Pre-Socratic philosophy is both a fundamental subject and an obscure one.

Executive Summary

PhilosopherNotable PhilosophySchool of Thought
Thales of MiletusWater as fundamental substanceMilesian School
AnaximanderApeiron as the source of all thingsMilesian School
AnaximenesAir as fundamental substanceMilesian School
HeraclitusDoctrine of changeHeraclitean School
ParmenidesUniformity of realityEleatic School
Melissus of SamosA single, unchanging and eternal substanceEleatic School
EmedoclesTheory of the Four ElementsPluralist School
AnaxagorasNous, cosmic mind, as the ordering principlePluralist School
DemocritusAtomic TheoryAtomist School
LeucippusCo-founder of AtomismAtomist School
PythagorasNumerical relationships and harmonyPythagorean School
PhilolausPythagorean cosmologyPythagorean School
XenophanesCritique of mythologyIndependent thinker
Diogenes of ApolloniaAir as the vital force of lifeIndependent thinker

Pre-Socratic Schools of Thought

The Pre-Socratic era, spanning several centuries and featuring the intellectual endeavors of over a dozen prominent philosophers, marked a pivotal period in the history of Western thought. During this time, numerous schools of thought emerged, each offering a distinct perspective on the fundamental nature of the cosmos and the underlying principles governing the universe.

The Pre-Socratic philosophers and the schools of thought they founded, unified solely by their shared commitment to observation and reason, challenged the prevailing mythological explanations of their time as they sought to uncover the mysteries of the natural world.

Milesian School

Founded by Thales of Miletus and continued by Anaximander and Anaximenes, this school focused on the search for a single, fundamental substance underlying all of reality.

Heraclitean School

Associated with Heraclitus, this school’s central idea was the concept of change – the view that everything is in a constant state of flux.

Eleatic School

Founded by Parmenides and continued by Zeno of Elea and Melissus, this school argued for the unity and immutability of reality, opposing the Heraclitean view of change.

Pluralist School

Associated with philosophers like Empedocles and Anaxagoras, this school proposed that reality consists of multiple fundamental substances or elements.

Atomist School

Founded by Leucippus and developed further by Democritus, this school introduced the atomic theory, suggesting that everything is composed of indivisible particles called atoms.


Epicurus founded the school of Epicureanism, which drew on atomistic principles and emphasized the pursuit of happiness and tranquility through philosophical means.

Pythagorean School

Founded by Pythagoras, this school emphasized mathematics as the key to understanding the universe, and explored the relationships between numbers and reality.

The Sophists

The Sophists were a group of itinerant teachers and philosophers who emerged during the late Pre-Socratic period. Although they did not form a single, cohesive school of thought like some other Pre-Socratic groups, they developed their own distinctive philosophical ideas, particularly in the areas of rhetoric and persuasion.

The Sophists are famous for their relativistic views – the belief that all knowledge is opinion – and infamous for appearing as Socrates’ antagonists in the Platonic dialogues.

The Pre-Socratic Philosophers

The Pre-Socratic philosophers, a diverse group of early Greek thinkers, pioneered the intellectual endeavor to understand the fundamental nature of reality through observation and reason. The methods and approaches they embraced – the search for fundamental principles through rational inquiry – had an enduring effect not only on ancient Greek philosophy but also on the history of Western thought.

In contemporary philosophy, the emphasis on critical thinking, logical reasoning and the systematic exploration of fundamental questions owes a debt to the work of the Pre-Socratic thinkers. Their legacy lies not only in the content of their ideas but also in the enduring spirit of inquiry they ignited.

The Milesian School

Thales of Miletus (c. 624-546 BCE)

Thales is considered the first philosopher in Western history, a title granted to him by Aristotle himself. He hailed from the ancient city of Miletus, which was part of Ionia (modern-day Turkey), giving rise to the name “Thales of Miletus”. Thales is known for his deep interest in natural phenomena and is often considered one of the earliest scientists as well as a philosopher.

Thales was interested in explaining natural phenomena through naturalistic and materialistic principles, which was a departure from earlier mythological explanations. He is famously associated with the idea that water is the fundamental substance (archê) from which everything in the universe is composed. This is often referred to as “hylozoism,” the belief that everything has a life force and is connected to water.

He made contributions to mathematics, particularly in the area of geometry, and is attributed with various theorems and practical applications.

Thales’ philosophical approach … the Milesian School, and his emphasis on seeking rational explanations for natural phenomena marked a significant shift in the history of thought.

Anaximander (c. 610-546 BCE)

Anaximander was a successor and student of Thales, known for his early explorations into the principles of existence and natural processes.

He proposed the concept of the “apeiron”, or the boundless, as the fundamental principle and substance underlying all of reality. He also made significant contributions to geography, cosmology and cartography, producing one of the earliest known maps of the world.

Anaximander’s idea of the “apeiron” was a departure from the earlier Milesian School and marked a shift toward more abstract and metaphysical thinking. His work laid the foundation for the development of metaphysical speculation in ancient Greek philosophy.

Anaximenes (c. 585-525 BCE)

Anaximenes, like Thales and Anaximander, was a philosopher from the Miletus school, and he continued the exploration of the fundamental substance of the universe.

Anaximenes proposed that air (aer) was the primary substance from which everything emerged, in the belief that air could condense to form other elements like water and further condense to become solid matter. He also made contributions to meteorology, attempting to explain natural phenomena such as thunder and lightning through his theories about air.

Anaximenes’ work is seen as an important development in early Greek philosophy, exploring the relationship between matter and change in the universe.

Heraclitean School

Heraclitus (c. 535-475 BCE)

Heraclitus was critical of relying solely on sensory perception to understand reality and believed that true understanding required a deeper, rational insight. Known as the “Obscure Philosopher”, he had a unique and enigmatic philosophical outlook.

Heraclitus is famous for the notion of change as a fundamental aspect of reality. He proposed that opposites are interconnected and necessary for each other. For example, he argued that conflict and tension are essential for harmony and balance in the world.

Heraclitus symbolized the ever-changing nature of reality with fire, viewing it as a potent symbol of transformation and the perpetual flux that characterizes the universe.

Eleatic School

Parmenides (c. 515-450 BCE)

Parmenides was a philosopher who explored the nature of reality and existence, particularly focusing on metaphysical questions.

Parmenides argued for the unity and immutability of reality. He believed that change and multiplicity were illusions, and that the true nature of reality is unchanging and indivisible.

Parmenides presented his ideas in a poetic form, describing two paths of inquiry — the Way of Truth, which led to knowledge of the unchanging reality, and the Way of Opinion, which was characterized by the deceptive appearances of the sensory world.

Parmenides’ ideas had a significant influence on Plato’s philosophy, famously encapsulated in the dialogue entitled “Parmenides”, where he explored the nature of reality and the challenges posed by Parmenides’ views.

Melissus of Samos (c. 5th century BCE)

Melissus was a philosopher who explored the nature of reality and made contributions to early Greek metaphysics. Melissus, like Parmenides, emphasized the unity and unchangeability of reality and argued that the universe is a single, unchanging and eternal substance.

Melissus critiqued the ideas of Parmenides, particularly Parmenides’ reliance on sensory perception, believing that sensory experiences could not provide accurate knowledge of the true nature of reality. This is possibly the first epistemological debate in the history of Western philosophy regarding rationalism and empiricism.

Melissus’ work represents a continuation of the metaphysical inquiries that characterized the Pre-Socratic period, and brought up a crucial and enduring debate in epistemology.

Pluralist School

Empedocles (c. 490-430 BCE)

Empedocles was a philosopher, poet and physician known for his contributions to early Greek thought, particularly in the fields of cosmology and metaphysics.

Empedocles proposed that everything in the universe was composed of four fundamental elements: earth, water, air and fire. He believed that these elements combined and separated under the influence of two opposing forces, Love (attraction) and Strife (repulsion).

Empedocles envisioned a cyclical universe in which the elements continually combined and separated due to the interplay of Love and Strife. This theory aimed to explain the creation and destruction of the world. The concepts of Love and Strife were not only metaphysical but also ethical principles that influenced his views on human behavior and the pursuit of wisdom.

Empedocles’ ideas had a notable influence on Aristotle, who later refined and adapted some of his concepts, particularly the idea of four elements.

Anaxagoras (c. 500-428 BCE)

Anaxagoras was a philosopher who made significant contributions to the study of nature and cosmology.

Anaxagoras proposed that a cosmic mind, or Nous, was the fundamental principle responsible for ordering and arranging the material world. He believed that the Nous gave order and purpose to the universe.

Anaxagoras criticized the idea of Empedocles’ four elements and instead argued that everything was composed of infinitely divisible particles called nous or nous-seeds.

Anaxagoras is often credited with introducing a more systematic and scientific approach to understanding the natural world. He studied and categorized various natural phenomena and attempted to explain them through rational principles.

Anaxagoras’ ideas influenced later philosophers, including the atomists and the development of atomistic theories.

Atomist School

Leucippus (c. 480-420 BCE)

Leucippus is often considered the founder of atomism, a significant early theory about the nature of matter.

Leucippus proposed that the universe was composed of indivisible and unchangeable particles called “atoms”. These atoms, according to his theory, were the basic building blocks of all matter. He argued that there was an infinite number of atoms with different shapes and sizes, and they combined and separated to form the various substances in the world.

Leucippus’ atomistic theory represented a rational attempt to explain the nature of matter, challenging earlier ideas about elements and providing a foundation for the scientific study of the physical world.

Leucippus’ ideas had a profound influence on his student Democritus, who further developed and popularized atomism.

Democritus (c. 460-370 BCE)

Democritus is best known for his development of atomic theory, which was a precursor to the modern conception of matter.

Democritus proposed that everything in the universe is composed of indivisible particles called “atoms”. These atoms are eternal, unchanging and exist in infinite varieties, differing in shape and size. In addition to atoms, Democritus introduced the concept of the void, or empty space. Atoms move through the void, and their interactions with each other in this empty space give rise to the properties and forms of matter.

Democritus believed in a deterministic universe, where natural phenomena is the result of the mechanical interactions of atoms. He asserted that everything had a natural cause and could be explained through the laws of nature.

Democritus’ atomic theory was influential in the later development and of philosophy of science.

Pythagorean School

Pythagoras (c. 570-495 BCE)

Pythagoras is a well-known philosopher and mathematician from ancient Greece who founded the Pythagorean School, a philosophical and religious movement that had a profound influence on both mathematics and philosophy.

The distinctive feature of Pythagorean philosophy was the notion of harmony in both the physical and metaphysical realms: the belief that numerical relationships and proportions underlay the structure of the cosmos and the nature of reality itself. This mystical and mathematical worldview influenced subsequent philosophical thought and had a lasting impact on the development of Western philosophy.

The Pythagorean School attracted students and followers who were not only interested in mathematics, but also in the broader pursuit of wisdom and spiritual enlightenment. The Pythagoreans delved into various areas of knowledge, including ethics, metaphysics, music and astronomy.

Philolaus (c. 470-385 BCE)

Philolaus was a Pythagorean philosopher and mathematician known for his contributions to mathematics and the Pythagorean school.

Philolaus was part of the Pythagorean tradition, a philosophical and religious movement founded by Pythagoras. Pythagoreans believed in the importance of mathematics and numbers in understanding the cosmos.

Philolaus, like other Pythagoreans, believed in the fundamental role of harmony and proportion in the structure of the cosmos. Philolaus made significant contributions to the study of numbers, and is sometimes credited with developing the theory of numbers as abstract entities with their own properties and relationships. This idea influenced later mathematical and philosophical thought.

Philolaus also proposed a cosmological model in which the Earth was not at the center of the universe, known as the “Central Fire” theory. He suggested that the Earth, along with other celestial bodies, moved around a central fire.

Independent Thinkers

Diogenes of Apollonia (c. 5th century BCE)

Diogenes of Apollonia was a philosopher known for his focus on fundamental principles and his role in advancing the naturalist approach to philosophy during the Pre-Socratic era.

Diogenes of Apollonia, believing that air was the primary substance (archê) of the universe, proposed that air was responsible for the generation and transformation of all things. He associated the concept of soul with breath (pneuma), believing that pneuma was the vital force that animated living beings. This idea was a departure from earlier theories about the soul.

Diogenes of Apollonia’s association of the soul with breath, or pneuma, had a lasting impact on subsequent philosophical and scientific thought. His ideas influenced later philosophers and contributed to the evolving understanding of life, consciousness and the relationship between the natural world and living beings.

Xenophanes (c. 570-475 BCE)

Xenophanes was a philosopher and poet who critiqued traditional beliefs, particularly in the realm of religion and theology. Xenophanes’ critical approach also extended to encompass skepticism about human knowledge on account of the subjectivity of perception and the inherent limitations of human understanding.

Xenophanes is known for his criticism of anthropomorphic gods in Greek mythology. He argued that traditional beliefs depicted gods in the image of humans and that these gods were not befitting of the divine. Xenophanes proposed a more abstract and philosophical conception of God as a single, all-encompassing and transcendent being. His was an early form of monotheism that arose in ancient Greece.

Xenophanes expressed many of his philosophical ideas through poetry, and his writings had a profound impact on the development of Greek literature and thought.

Sources of Information

There are no no complete works in existence that can be attributed to the Pre-Socratic philosophers, for no such text survived to the present day. What we know about their ideas and contributions comes from references and fragments found in the writings of later philosophers, historians and commentators.

For example, Aristotle, who lived after the Pre-Socratic era, extensively discussed their ideas and frequently quoted or summarized their views in his own writings. Likewise, other authors such as Plato and Diogenes Laërtius made references to the Pre-Socratic philosophers in their works.

There are four primary sources — Aristotle, Plato, Diogenes Laërtius and Sextus Empiricus – for the historical reconstruction of Pre-Socratic philosophy. Their writings often included references to lost works of the Pre-Socratics, and occasionally even passages, that have enabled scholars to identify and piece together their ideas and perspectives.

The absence of complete writings presents a substantial challenge for historians and philosophers who seek to reconstruct the Pre-Socratic philosophical systems. Nevertheless, the surviving fragments and references offer valuable information about the early development of Greek philosophy.

Aristotle (384 – 322 BCE)

Aristotle is considered the most significant source for our understanding the Pre-Socratic philosophers. His extensive writings, including “Metaphysics”, “Physics” and “On Generation and Corruption”, contain valuable information, detailed discussions and interpretations of their ideas.

Diogenes Laërtius (c. 3rd century CE)

Diogenes Laërtius’s work, “Lives and Opinions of Eminent Philosophers”, often refered to as “The Lives of the Philosophers”, provides invaluable biographical information and summaries of the philosophical doctrines of various ancient philosophers, including the Pre-Socratics. While not as systematic as Aristotle, his work is an important historical resource.

Plato (c. 428 – 348 BCE)

Plato occasionally mentioned Pre-Socratic philosophers in his dialogues, sometimes indirectly and sometimes by name, including a description of their views, however brief, and their memorable contributions to ancient Greek culture. For instance, he indirectly mentions Anaxagoras’ natural philosophy in The Apology and discusses Parmenides’ philosophy in the dialogue entitled “Parmenides”.

Sextus Empiricus (c. 2nd century CE)

Sextus Empiricus, a later philosopher and physician, although not as prominent as the others, also referenced and discussed the ideas of Pre-Socratic philosophers in his work “Outlines of Pyrrhonism”.

Aristotle, Plato, Diogenes Laërtius and Sextus Empiricus are the primary, by virtue of being the most extensive and explicative, sources for our knowledge of the Pre-Socratic philosophers. There are, in truth, a myriad of ancient sources on the subject, each of whom has contributed a piece of this historical and intellectual puzzle.

However, there are but a handful noteworthy and yet unmentioned commentators who contributed significantly to our understanding of Pre-Socratic philosophy.

Herodotus (c. 484 – 425 BCE)

Although primarily known as a historian, Herodotus occasionally mentioned the views and activities of some Pre-Socratic thinkers in his historical accounts, but his primary focus was on history rather than philosophy.

Theophrastus (c. 371 – 287 BCE)

Theophrastus, a student of Aristotle, wrote a treatise called “Opinions of the Natural Philosophers”, or “Physikai Doxai”, which included information about the Pre-Socratic philosophers, but his work is relatively limited compared to other sources.

Aetius (c. 1st century BCE)

Aetius, also known as Aëtius of Antioch, was an ancient philosopher and compiler of philosophical texts. His work, “Placita”, includes summaries of various philosophical doctrines, including those of the Pre-Socratic philosophers, but his work is less extensive compared to the above sources.

Hippolytus of Rome (c. 2nd century BC)

Hippolytus was an early Christian theologian who wrote a work called the “Refutation of All Heresies”, or “Philosophumena”, in which he discussed various philosophical schools, including those founded by the Pre-Socratics, but his work is primarily focused on theological concerns.

While these additional sources may not be as extensive as the four previously mentioned, they still contribute to our understanding of the Pre-Socratic philosophers.

Collectively, these ancient writers and historians provide a wealth of information that helps modern scholars piece together the early history of Greek philosophy.

Final Thoughts

Socrates, Plato and Aristotle, collectively referred to as the Athenian School, redirected philosophical inquiry from the natural world to the realm of ethics, politics and epistemology. Socrates’ focus on self-examination and ethical virtue, Plato’s exploration of ideal forms and the nature of knowledge, and Aristotle’s systematic approach to understanding the world through observation and reason marked a significant shift in the history of philosophy.

This transition expanded the scope of philosophical inquiry to encompass ethics, politics and human nature, and gave rise to what we now consider classical Greek philosophy.

From the classical period, philosophy continued to evolve, with contributions from Hellenistic, Roman, Medieval, Renaissance and Enlightenment philosophers, each adding depth and complexity to the discipline.

The modern era ushered in new approaches, including empiricism, rationalism, existentialism and analytical philosophy, further expanding the boundaries of human understanding.

Throughout the centuries, philosophy has continually adapted to the ever-changing intellectual landscape, reflecting the concerns and questions of its time.

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