Q: Why did Thales believe that everything was water?
Thales of Miletus was an astute and observant guy, and like to seek and find patterns in things… But you have to remember… he lived 2600 years ago…
“Thales of Miletus (c. 624/623 – c. 548/545 BC) was a Greek mathematician, astronomer and pre-Socratic philosopher from Miletus in Ionia, Asia Minor (West coast of present day Turkey).
He was one of the Seven Sages of Greece. Many, most notably Aristotle, regarded him as the first philosopher in the Greek tradition, and he is otherwise historically recognized as the first individual in Western civilization known to have entertained and engaged in scientific philosophy.
Thales is recognized for breaking from the use of mythology to explain the world and the universe, and instead explaining natural objects and phenomena by naturalistic theories and hypotheses, in a precursor to modern science.
Almost all the other pre-Socratic philosophers followed him in explaining nature as deriving from a unity of everything based on the existence of a single ultimate substance, instead of using mythological explanations.
Aristotle regarded him as the founder of the Ionian School and reported Thales' hypothesis that the originating principle of nature and the nature of matter was a single material substance: water.
In mathematics, Thales used geometry to calculate the heights of pyramids and the distance of ships from the shore. He is the first known individual to use deductive reasoning applied to geometry, by deriving four corollaries to Thales' theorem. He is the first known individual to whom a mathematical discovery has been attributed.
But you are asking “WHY?”… “Why did he think, and suggest as he did?”
I can only take a guess…
First: “Water” to the Greeks of the time…
“Water is one of the elements in ancient Greek philosophy, in the Asian Indian system Panchamahabhuta, and in the Chinese cosmological and physiological system Wu Xing. In contemporary esoteric traditions, it is commonly associated with the qualities of emotion and intuition.”
“Water was one of many archai proposed by the Pre-socratics, most of whom tried to reduce all things to a single substance. However, Empedocles of Acragas (c. 495 – c. 435 BC) selected four archai for his four roots: air, fire, water and earth. Empedocles roots became the four classical elements of Greek philosophy”
Source: Water (classical element) - Wikipedia
So it largely comes down to a predisposition to find a “single substance”.
Water is a very good choice. (Wrong. But a really good choice).
He would have surely seen whirlpools,
and then notice the same patterns in growth, as a first guess.
And he would be aware of what happens when things die and dehydrate:
Also… Turkey can get snow. Though near the coast, likely not commonly.
So he may have stumbled onto:
He wouldn’t have had any way to know that the snowflake is an assembly, made from some 20,000,000,000,000,000,000 water molecules. So the shape of snowflakes might have been seen by him as “1 solid water”.
Seeing them things around him taking their shape from other identifiable shapes, he likely read too much into it.
He had the right idea, about “water driving the shapes of life”… it clearly and actually does. There is more to it of course.
And he and his buddies were definitely correct, there is a single underlying lowest common denominator, and it is the cause of the shape of life, but is also the cause of the patterns of water.
He overextended his claim. But was heading down the right track in some big ways… he just went too far. A couple of stops past the station he should have stopped at.