Anaximander of Miletus
ἈναξίμανδροςThe first to draw the world and to think the boundless
Anaximander, pupil of Thales, made the decisive abstraction: the source of all things cannot itself be any one thing. If water were primary, it would overwhelm its opposite, fire. So the origin must be indeterminate — the apeiron, boundless and ageless, out of which opposites separate and into which they return, paying 'penalty to one another for their injustice according to the ordinance of time.'
The first truly abstract concept in Western thought: a principle defined not by what it is but by what it lacks — limit, determination, decay. The arche is lifted out of the sensible world entirely.
Anaximander suspended the Earth in the centre of the cosmos, held by nothing, equidistant from all things and so with no reason to move. It is arguably the first argument from symmetry — and it abolished the need for Atlas, turtles, or pillars.
He held that the first animals arose from moisture and that humans must have developed from creatures of another kind, since a human infant could not have survived unaided. A naturalistic origin of life, twenty-four centuries before Darwin.
Credited with the first map of the inhabited world and with introducing the gnomon (a vertical rod) to Greece to mark solstices and equinoxes. To map and to measure time is to claim the world is regular.
Where Thales named a substance, Anaximander named a structure. He showed that explanation could climb above the senses into pure concept — and that the cosmos could be modelled, mapped, and reasoned about as a balanced system. This is theory in the modern sense.
The apeiron prefigures every modern appeal to an underlying field, vacuum, or symmetry from which determinate things emerge. Cosmology as a mathematical science starts here.