The pre-Socratic philosophers were thinkers within the Western intellectual tradition (mostly) preceding the life Socrates (c. 469 – c. 399 BCE) living in Ionia (coast of modern-day Turkey), Italy, and Greece. Some of these thinkers were also contemporaneous with Socrates, such as Democritus (d. 371 BCE) and Parmenides (d. 450 BCE). There are three pre-Socratic schools: the Ionians (who held to corporeal monism), Italians (incorporeal monism), and Athenians (corporeal pluralism).
The Ionian Philosophers
There were four major thinkers from the Ionian tradition: Thales of Miletus (d. 546 BCE), Anaximander (d. 547 BCE), Anaximenes (d. 528 BCE), and Heraclitus (d. 475 BCE), all of whom were united by four common beliefs. First, they were naturalistic in outlook. They sought naturalistic rather supernatural explanations that involved the gods. This was a dramatic turn in an ancient world in which polytheism (belief in many gods) and the influences of the gods in human affairs was widely believed. The Ionians, one could say, were the first natural scientists. Secondly, they were all materialists. They believed that all that exists is matter and that this matter is eternal. Third, they were corporeal monists, which is the conviction that all existing things can be reduced to one common substance although the Ionians disagreed on what this substance is. Fourthly, they were hylozoists in that they all subscribed to the idea that there is a form of life in all material objects.
Thales of Miletus is often said to be the first natural scientist in the Western tradition as well as the person with whom western philosophy began. He was also a noted mathematician and businessman who had a good understanding of geometry and astronomy. According to tradition, Thales predicted an eclipse of the sun in 585 BCE and that while in Egypt, he measured the height of the Great Pyramids using their shadows. He could calculate the distance that ships were from the shore and he theorized concerning the size of the sun and moon. He is most well-remembered for his belief that water is the basic substance of all things. Everything is made from water, which he thought is a fundamental and important part of human existence. He also believed that the Earth is a disk that sat upon an ocean of water. Experience would have informed Thales that all life required water for its survival and that without it things tended to die. It wouldn’t thus be out of the park for an ancient to have theorized that water is the underlying substance of all things. Water can also take three different forms: solid, liquid, and gas. All things, according to Thales, constitute one of these three forms.
Anaximander, whose work touches metaphysics, geography, biology, and astronomy, was a student of Thales. However, his answer to the question of a primary substance disagreed with his teacher’s notion of water. Anaximander used the term apeiron (the boundless) to denote an undefined substance behind everything. All things originate within this substance that life will return to when it dies. Whatever the boundless is, Anaximander describes it as unlimited, immortal, unborn, and impersonal. He was also the first evolutionist in that he posited the first creatures to have originated from a moist element through evaporation and that human beings originated from some other kind of animal. Material gradually developed into different forms.
Anaximenes believed that the fundamental substance is air and that all existing things were at some point air before natural forces acted upon them. When the air was acted upon, it transformed into other materials. This is Anaximenes’ theory of the origin of the world. Anaximenes also claimed wind, cloud, and water to be modifications of the substance of air rather than distinct substances. Also important was Anaximander’s use of experience when explaining the world; for example, he explained meteorological observations of things like thunder, lightning, hail, rainbows, and earthquakes on observational and experiential grounds, viewing them as natural phenomena.
Heraclitus, sometimes called the weeping philosopher of Ephesus because of his melancholic disposition, said the fundamental substance is everliving fire. He also famously quipped that one can never step into the same river twice. This has been interpreted as him communicating his conviction that all things are in a state of flux and therefore in perpetual change. Despite this, the world remains stable and, although parts of it are consumed by fire at any given time, the whole remains. Heraclitus also introduced the term and concept of logos, according to which all things are one.