The Classical Greeks to the Onset to the Hellenistic Era

Thales of Miletus

Considered the first philosopher; believed the universe was composed of physical substances governed by natural principles and proposed water as the fundamental substance.

Anaximander

Rejected water as the physis; argued for a boundless, eternal substance and suggested an early concept of evolution.

Heraclitus

Known for the idea of constant change; believed in the concept 'you cannot step in the same river twice' and saw fire as the fundamental element.

Pythagoras

Believed numbers were the essence of reality; introduced the idea of two worlds: the abstract and the material.

Empedocles

Proposed that everything was made up of four 'roots' influenced by love and strife; contributed to early theories of personality.

Democritus

Developed the theory of atomism; suggested that all things, including the soul, are composed of indivisible atoms.

Socrates

Focused on ethical learning and self-knowledge; argued that virtue comes from understanding the essence of things.

Plato

Developed the Theory of Forms; proposed a tripartite soul and viewed knowledge as innate, influencing cognitive psychology.

Aristotle

Emphasized empirical observation and classification; introduced a hierarchy of souls and formulated the Laws of Association.

Hippocrates

Proposed that mental and physical health depended on the balance of four humors, influencing early theories of personality and mental illness.