Diogenes Laertius was a Roman-era historian, and the main source of biographical information on ancient philosophers. He wrote in Greek.

What is Philosophy?

As a term, Philosophy has a very clear etymological meaning: it is derived from the Greek “philos” (friend) and “sophia” (wisdom), and connotes the fondness of knowledge, or of wisdom. Pythagoras is thought to have had spoken himself in favor of using this term so as to refer to the people who were involved in thinking, instead of calling them by the previously used “sophos” (wise; sage), arguing that a human can only aspire to be wise, but never actually possess wisdom.

Historically, the first Greek philosophers become distinct from the previous “sages” due to focusing on physical, instead of divine, matters. The historian of philosophy, Diogenes Laertius (180-240 AD) who wrote about the lives and teachings of eminent philosophers of antiquity, presents the following notable categorizations of philosophy:

Two types (or schools): the Ionian school, and the Pythagorean – or Italiotic – school.

Three categories of philosophical interest: natural philosophy, dialectic philosophy, and ethical philosophy.





And English edition of the treatise concerning the important ancient Philosophers, by Diogenes Laertius.

As a term, Philosophy has a very clear etymological meaning: it is derived from the Greek “philos” (friend) and “sophia” (wisdom), and connotes the fondness of knowledge, or of wisdom.

The Ionian School

Traditionally, the first philosopher is regarded to be either Thales of Miletus, or his student, Anaximander of Miletus. There are two main reasons why Thales is at times not identified as the first philosopher: he didn’t leave any written work behind, and he lived in the last part of the era of prominence of “sages”, when theologians also produced work which contained philosophical elements. After all, Thales is the only philosopher to be included in the list of “The Seven Sages of Greece”, with inscriptions of his teachings found at the Oracle of Delphi.

Nevertheless, Thales is known for coming up with influencial new notions. The notion of the “theorem”, in mathematics, is attributed to him; as is the first mathematician proof of a theorem (Aristotle, and Euclid, both mention Thales as the source of the first theorem). It is on the properties of geometrical analogies.

Anaximander, his student, did write down his theories; although only a very small fragment survives. In that fragment we read of the first use of a noun-form for the notion of something “infinite”; the Infinite, in Anaximander, is a boundless and unknown space, from which all things originate, and to which all things return when they pass away. The notion of the Infinite played a crucial role in all philosophy, as well as in mathematics and the natural sciences. Prior to Anaximander, the Greek term for the "infinite" existed only in the form of an adjective; Homer, for example, uses it to describe the sea.

The so-called “Ionian school” - the name is given due to its founders originating in the region of Ionia, in Greek Asia Minor – is argued to be more involved with natural philosophy, and to stay away from obscure or theological ideas. In that it is in direct contrast to the “Pythagorean” school.

Thales is known for coming up with influencial new notions. The notion of the “theorem”, in mathematics, is attributed to him; as is the first mathematician proof of a theorem.

The Pythagorean School

It was also called “Italiotic”, by Diogenes Laertius, because its founder, the illustrious Pythagoras, emigrated to the Greek colonies in Italy, and later important figures of this school were from colonies in Sicily and south Italy: Parmenides of Elea, his student Zeno, also of Elea, and Empedocles of Akragas. The common trait in those philosophers is that they were primarily interested in either mathematician or dialectic thought. Pythagoras and his students had presented highly significant mathematical theorems (two famous examples are the “Pythagorean Theorem”, and the “Proof that the square root of 2 is not a rational number”; the first one is attributed to Pythagoras himself, the second to his student, Hippasus of Metapontum). Pythagoras also provided the first method of musical notation, which was based, again, on mathematics.

Pythagoras did refer to a divine character of numbers and geometry. The Eleans, Parmenides and Zeno, were equally interested in a distinction between the natural world (that is, the world we identify through our senses), and a possible unseen world. Parmenides was of the view that literally nothing in the thoughts of a human can be tied to a truth; and that there would exist a different plane, where truth was known, but forever to remain out of reach for human thinkers. Zeno constructed a famous treatise, which became known as “the paradoxes”. According to Plato (in his dialogue titled “Parmenides”) Zeno didn’t mean to prove that his teacher’s claims were correct, but simply to show that those who made fun of the claims by Parmenides may be presenting even greater paradoxes, if their reasoning is to be examined thoroughly. The Elean philosophers maintained that every notion we form so as to account for things we pick up through our senses (for example: our notion of size, or movement) may be just illusory, and have to do with the human mind only, instead of being in any manner tied to a reality of the (external) world.

Thales of Miletus

Pythagoras and his students had presented highly significant mathematical theorems (two famous examples are the “Pythagorean Theorem”, and the “Proof that the square root of 2 is not a rational number”.

On the difference between Natural, Dialectic, and Ethical Philosophy

The other main categorization that Diogenes Laertius presents is the one about the major types of philosophy.

Natural philosophy as a term was still in use in the late 18th century; Issac Newton was officially described as a “natural philosopher”. It is the examination of properties and relations of objects in the physical world. “Physics”, as a term, signified the same in ancient Greek Philosophy.

Dialectic philosophy is the philosophy of notions which may be existing solely as mental phenomena; that is they do not have to be tied in any way to the physical world. A good example of such a notion is found in the Platonic treatises about the use of terms so as to refer to physical objects; Socrates routinely argues that a thought expresses only a relative – and furthermore one highly ambiguous – tie to external reality. In practical terms one can communicate using words, and by expressing thoughts, but on a deeper level the use of language appears to be only functioning due to its significance for the person who is using it: thoughts appear to be schemata of largely fleeting and unaccountable mental procedures, which only due to practical need serve as a means to describe realities in the physical world. Mathematical thinking is often identified as a prime use of dialectical modes of thought. The first use of the notion of the Infinite, in a mathematical proof, is argued by Aristotle to have been provided by a student of Plato’s Academy, in an attempt to present how a circle (an image with a periphery that has no vertices at all) can be approximated by a regular polygonal surface which would increase the number of its own vertices exponentially.

Ethical philosophy is the philosophy which deals with the way of life a person should lead, in order to achieve a set goal. The goal is often happiness; the Greek “eudaimonia”, or virtue. Ethical philosophy flourished only after the age of Socrates and the sophists; up to then virtually all philosophical treatises were on either natural philosophy or dialectics.

Aristotle (right) and Plato (left), in Raphael's painting "The School of Athens".

© 2018 Kyriakos Chalkopoulos