Thales of Miletus was a highly-esteemed ancient Greek philosopher (620 BCE – 546 BCE), whose discourse ranged widely from mathematics to history to astronomy to science to politics. He was most well-known for determining the solstices (setting the seasons), predicting a solar eclipse on May 28 585 BCE, formulating five Euclidean geometric theorems, and, most importantly for our work together in this class, describing water as the Primary Principle. Plato considered him to be one of the Seven Sages of Ancient Greece; in fact, he was first on the list.
On Thales’ description of water as Primary Principle, according to Aristotle:
Aristotle defined wisdom as knowledge of certain principles and causes (Metaph. 982 a2-3). He commenced his investigation of the wisdom of the philosophers who preceded him, with Thales, the first philosopher, and described Thales as the founder of natural philosophy (Metaph. 983 b21-22). He recorded: ‘Thales says that it is water’. ‘it’ is the nature, the archê, the originating principle. For Thales, this nature was a single material substance, water. Despite the more advanced terminology which Aristotle and Plato had created, Aristotle recorded the doctrines of Thales in terms which were available to Thales in the sixth century BCE Aristotle made a definite statement, and presented it with confidence. It was only when Aristotle attempted to provide the reasons for the opinions that Thales held, and for the theories that he proposed, that he sometimes displayed caution.
Source: O’Grady, Patricia. Thales of Miletus – The Internet Encyclopedia of Philosophy. Adelaide: The Flinders University of South Australia, September 17, 2004 http://www.iep.utm.edu/thales/#H13