Thales is credited in later Greek testimony with seeking a natural first principle, identifying water as the source of things and explaining celestial events without mythic genealogy.
Intellectual setting
Later authors made Thales the first in a Milesian sequence, but the evidence consists of retrospective reports rather than surviving work.
Key ideas
Water as principle
Reports credit Thales with explaining the world from water, a proposal later philosophers could criticize and refine.
Natural inquiry
His reputation as an astronomer and geometer made him a canonical starting point for Greek explanatory inquiry.
Legacy
Thales remains the conventional opening figure in histories of Presocratic philosophy because later authors saw in him a turn toward natural explanation.