Imaginary portrait of Anaximenes of Miletus, from the Nuremberg Chronicle, 1493 (

Imaginary portrait of Anaximenes of Miletus, from the Nuremberg Chronicle, 1493 (

Anaximenes of Miletus

OCTOBER 14, 2022

Anaximenes was the third of the three Ionian pre-Socratic philosophers from Miletus, on the west coast of Asia Minor. The Milesian school (600 – 530 B.C.E.) began with Thales, who...

Scientist of the Day - Anaximenes of Miletus

Anaximenes was the third of the three Ionian pre-Socratic philosophers from Miletus, on the west coast of Asia Minor. The Milesian school (600 – 530 B.C.E.) began with Thales, who was joined by Anaximander, and then by Anaximenes.  We discussed Thales in a post last week, and announced that in future posts, we would be visiting as many as possible of the pre-Socratic natural philosophers, those who speculated on the nature of matter and the origin and structure of the world. Thales had established the tone and direction of Ionian philosophy by looking for natural causes and refusing to invoke supernatural explanations or the whimsical interventions of gods.  Thales thought that the primordial element of the world was water, and believed that the drum-shaped earth floated on water, and suffered earthquakes when waves in the subterranean seas battered the Earth.   Because he relied only on rational explanations, this meant that rational humans could discuss and criticize such explanations, and this is exactly what happened.  Anaximander disagreed with Thales’ conclusion that water was the primordial element of the world, and so did Anaximenes, even though all three were part of the same philosophical school – the first philosophical school.  Ordinarily, we would discuss Anaximander next, since he was junior to Thales but older than Anaximenes.  But because our library unexpectedly closed this week because of a water-main problem, and I am cut off from my modest library of Anaximander literature, I am discussing Anaximenes next.  And logically, this is a good choice, for as we shall see, Anaximenes' philosophy was closer to that of Thales than Anaximander, who would make a radical break when opting for a fundamental substance.

As with Thales, we know next to nothing about Anaximenes the person.  He was born about 585 B.C.E. and died around 528.  We don't even have any human-interest stories involving Anaximenes, as we did with Thales.  Like Thales, Anaximenes wrote no book, or at any rate, none has survived.  We know about him only through the doxographic tradition, from later philosophers such as Aristotle and Plato, whose works DID survive.  While Thales did not leave behind a single written fragment, we do have one quotation from Anaximenes: “Just as our soul, being air, constrains us, so breath and air envelop the whole cosmos.”  That is a nice fragment to have, as it pertains to Anaximenes’ principal contribution to the Milesian school.  Anaximenes thought that if there was one fundamental element out of which the world was fashioned, then it was more likely to be air than water.

Anaximenes’ choice was based on his observation that air exists in different states.  Air can be rarefied, and it can be compressed. Moreover, as air is compressed, it cools, and when rarefied, it warms.  Thus he was able to argue that one substance, in different states, can produce different qualities, like hot and cold.  And with two opposite qualities, one can form a variety of substances by mixture.  Later Greeks, like Aristotle, would account for the entire world with just four qualities and a primordial matter.

What really endears Anaximenes to historians of science is that he suggested a demonstration to confirm that hot and cold emerge from different states of air.  Purse your lips and blow on your hand, he proposed.  The air feels cool.  Not open your lips and let the air expand and rarefy.  Your breath now feels warm. We would explain the results differently.  But we have to admire that Anaximenes has attempted to confirm a hypothesis with an experiment.  It appears to be the first such hypothesis-driven experiment ever.  Granted, we do not know for sure that Anaximenes did this – the story comes to us from Plutarch, who lived 600 years later than the Milesians.  But since all our evidence concerning Anaximenes is tenuous, we might as well include the story, if we are going to allow that Anaximenes existed at all.

As with Thales, there are no contemporary or even Hellenistic portraits of Anaximenes.  So we use for a portrait a woodcut that was included in the Nuremberg Chronicle of 1493, a book we do not have in our Library.  I like it, because it has his name right there, and it does look old.

Our next stop will be Anaximander of Miletus, who, with his proposal that the fundamental substance is a substance with no properties at all, would take Ionian natural philosophy to another level.

William B. Ashworth, Jr., Consultant for the History of Science, Linda Hall Library and Associate Professor emeritus, Department of History, University of Missouri-Kansas City. Comments or corrections are welcome; please direct to