Anaximenes
Said air is the source of all, transformed by condensation and rarefaction.
Overview
The third Milesian, Anaximenes made a crucial methodological advance: he explained how the fundamental stuff becomes everything else. He held that air (aēr) is the basic principle, and that all other substances arise through condensation (cooling into wind, cloud, water, earth, stone) and rarefaction (thinning into fire). This gave a single mechanism for qualitative change — a genuine scientific hypothesis linking a substance to a process.
What they supported — and why
Air is the archē
SupportedEverything is a form of air at different densities.
WhyAir is limitless yet definite, and clearly related to life and breath; unlike the vague apeiron it is observable and can be shown transforming.
Condensation and rarefaction
SupportedRarefied air becomes fire; condensed air becomes wind, cloud, water, earth, stone.
WhyA single quantitative process (density) can generate all qualitative differences — the first mechanism of change in physics.
Causes championed
- Explaining change by mechanism
- Unifying diverse phenomena under one process
Issues wrestled with
- How does one substance become the many?
- What process drives natural change?
Hurdles faced
- Reconciling a single origin with the obvious variety of the world
Works & books
1 catalogued. Status shows how much survives to today.
On Nature
Fragments onlyProse treatise; survives in fragments and testimonia describing air and the condensation/rarefaction mechanism.
The influence network
See Anaximenes in the map →Influenced by
Influenced
In their words
“As our soul, being air, holds us together, so breath and air surround the whole cosmos.”
— paraphrase via Aetius
Legacy
By tying substance to a measurable process, he modeled how scientific explanation should work — arguably a deeper contribution than his choice of 'air'.
Further reading
Cross-checked against these authoritative references.