The pre-Socratic philosophers were early Greek thinkers from the 6th and 5th centuries BCE who preceded Socrates and laid the groundwork for Western philosophy. They primarily focused on cosmology, the nature of reality, and the origins of the universe. Here’s a list of notable pre-Socratic philosophers, along with quotes attributed to them:

1. Thales of Miletus • Main Ideas: Considered the first philosopher. He believed that water was the fundamental substance underlying everything.
   • Quote: “Water is the principle of all things.”
2. Anaximander • Main Ideas: Introduced the concept of the “Apeiron” (the infinite or boundless) as the origin of all things.
   • Quote: “The infinite is the origin of all things.”
3. Anaximenes • Main Ideas: Argued that air is the primary substance from which all things come and to which they return.
   • Quote: “Just as our soul, being air, holds us together, so do breath and air encompass the whole world.”
4. Pythagoras • Main Ideas: Focused on numbers and mathematical harmony as the essence of the world.
   • Quote: “All things are numbers.”
5. Heraclitus • Main Ideas: Known for his doctrine that everything is in a state of flux and for the unity of opposites.
   • Quote: “You cannot step into the same river twice, for other waters are continually flowing on.”
6. Parmenides • Main Ideas: Contrasted Heraclitus by arguing that change is an illusion, and reality is unchanging and indivisible.
   • Quote: “What is, is, and what is not, cannot be.”
7. Empedocles • Main Ideas: Proposed that all matter is composed of four roots (elements): earth, air, fire, and water, mixed by love and separated by strife.
   • Quote: “God is a circle whose center is everywhere and circumference nowhere.”
8. Anaxagoras • Main Ideas: Introduced the notion of Nous (Mind) as the force that arranges all matter.
   • Quote: “All things were together, infinite both in quantity and in smallness; for the small too was infinite.”
9. Democritus • Main Ideas: Along with his teacher Leucippus, proposed an atomic theory of the universe.
   • Quote: “Nothing exists except atoms and empty space; everything else is opinion.”

These philosophers and their ideas represent the beginning of Western philosophical thought, emphasizing rationality and inquiry into the natural world and human existence. Their teachings continue to influence contemporary thought across various disciplines.