It is not known why Thales turned away from the traditional beliefs which attributed all natural events and man's fortunes and misfortunes to the great family of Olympian gods, but Miletus was the most prosperous of the Ionian cities, and it cannot be doubted that the flourishing merchants believed that their prosperity resulted from their own initiative and endeavours. Thales's great philosophical pronouncement that water is the basic principle shows that Thales gave no acknowledgement to the gods as instigators and controllers of phenomena. Thales's hypotheses indicate that he envisaged phenomena as natural events with natural causes and possible of explanation. From his new perspective of observation and reasoning, Thales studied the heavens and sought explanations of heavenly phenomena.

Thales is the first person about whom we know to propose explanations of natural phenomena which were materialistic rather than mythological or theological. His theories were new, bold, exciting, comprehensible, and possible of explanation. He did not speak in riddles as did Heraclitus, and had no need to invent an undefined non-substance, as Anaximander did. Because he gave no role to mythical beings, Thales's theories could be refuted. Arguments could be put forward in attempts to discredit them. Thales's hypotheses were rational and scientific. Aristotle acknowledged Thales as the first philosopher, and criticized his hypotheses in a scientific manner.

The most outstanding aspects of Thales's heritage are: The search for knowledge for its own sake; the development of the scientific method; the adoption of practical methods and their development into general principles; his curiosity and conjectural approach to the questions of natural phenomena - In the sixth century B.C.E., Thales asked the question, 'What is the basic material of the cosmos?' The answer is yet to be discovered.