- Academy School of Philosophy
- See: Plato.
- Anaxagores of Clazomenae (5th century)
- The universe was composed of “seds” of every distinct substance so that “everything has a share of everything.” Changes occurred as a result of the rearrangement of its constituent substances.
- Anaximander of Miletus (6th century)
- The origin of all things was “the unbounded,”which was divine, immortal, and indestructible. It controlled and “enfolded” the kosmos (“good order”).
- Anaximenes of Miletus (mid 6th century)
- Air was the substance from which everything is made – fire, water, earth, and everything in the world.
- Antisthenes
- He was the founder of the Cynics school of philosophy. Happiness was based on virtue, which consisted of action and was a practical quality to be taught.
- Aristippus, the Younger, of Cyrene
- He founded the Cyrenaic school of philosophy. Knowledge is based on sensation, and the present moment is the only reality, so immediate pleasure should be a person’s primary aim in life.
- Aristotle (384-322)
- He established the Peripatetic school of philosophy (the Lyceum). The universe must have a single unchanging cause. Also, the soul and the body were two aspects of a single being.
- Cynics School of Philosophy
- This was a group of philosophers who followed the principles of Antisthenes and Diogenes.
- Cyrenaic School of Philosophy
- See: Aristippus, the Younger, of Cyrene.
- Democritus
- See: Leucippus and Democritus.
- Diogenes
- Happiness came from self-sufficiency, which could be achieved by self-discipline and a loss of the conventional sense of shame.
- Eleatic School of Philosophy
- See: Parmenides.
- Empedocles (???-432)
- The four elements – earth, air, fire, water – were eternally distinct but were combined to create everything under the influence of Love and Strife.
- Epicurus (341-270)
- Happiness came from attaining a tranquility of mind derived from a proper understanding of the natural world, and pleasure was good.
- Eucleides of Megara
- See: Megarian School of Philosophy.
- Heracleitus (fl. c500)
- The world had an underlying unity which depended upon a balance between opposites; thus, everything was in a state of flux. The essential material of the universe was fire.
- Leucippus and Democritus (mid to late 5th century)
- Everything was created by the chance collision of solid particles that were homogenous and individual and which continued to move through an infinite void in infinite numbers.
- Megarian School of Philosophy
- It was founded by Euclides of Megara. It adopted the beliefs of the Eleatic school of philosophy.
- Parmenides (early 5th century)
- He founded the Eleatic school of philosophy. The essential matter (“what exists”) was single, unchanging, and indivisible.
- Peripatetic School of Philosophy
- See: Aristotle.
- Plato (c429-347)
- He established the Academy school of philosophy (c385). A duality existed between the soul and the body, and the soul was aware of the world of Ideas before birth, so that knowledge came from the soul’s recollection of the world of Ideas.
- Pyrrhon
- He founded the Sceptics school of philosophy. Knowledge of the true nature of things was unattainable because the senses were unreliable and the teachings of the dogmatic philosophers were contradictory.
- Pythagoras (fl. 530)
- The universe was created by the Heaven inhaling the Infinite or Void to produce groups of units or numbers. All things in the universe were actually numbers and had a position in the cosmos.
- Sceptics School of Philosophy
- See: Pyrrhon.
- Socrates (469-399)
- Philosophers should study ethics and human relationships rather than the natural and physical world.
- Stoics School of Philosophy
- The school was founded by Zeno of Citium. The universe was controlled by reason, so that whatever happened was divinely ordained by reason.
- Thales of Miletus (early 6th century)
- The world and everything in it originated as water and eventually would return to it.
- Xenophanes (late 6th to early 5th centuries)
- There was a single eternal god who did not resemble humans and who caused things to happen by mind alone.
- Zeno (5th century)
- He produced arguments intended to reduce the arguments of his opponents to absurdity by illustrating the contradictions within them.
