Anaximenes was an ancient Greek philosopher born in Miletus in the midle of the 6th century BC. Western philosophy is said to have been born in Miletus, Greece and Anaximenes is the third in a line of thinkers following his teachers Anaximander and Thales. What Anaximenes is best known for is taking the concept that there is a fundamental principle of reality (arche) and saying that air is that principle. Thales had originally thought it was water, an element, and Anaximander thought it was an indefinite thing which he called the apieron (“without limit”). Anaximenes decides it is an element after all, but an element capable of changing into all the other elements.

Anaximenes explains that air can become rarer or denser. When it does, it changes into the other elements. For example, when thinned, it becomes fire. When condensed, it becomes wind, then clouds, then water, earth and stone. From these elements, all the other things in the world follow. In ancient Greece there will develop the concept of the four elements: earth, water, wind and fire. As we already see here with Anaximenes, he shows how these elements go from the most dense to the least thin.

Anaximenes supported this understanding with a simple observation. When you blow with your mouth relaxed, the air that comes out is hot. But when you purse your lips together, the air that comes out is cool. In this way, he believed that the thinner air is, the hotter it will be. But the denser it is, the cooler it will be. This is why stones are naturally cooler than fire. This view was very important because not only did it present a fundamental principle, air, to explain the world, it also introduced a mechanism to explain change. This view is foundational for Western science, what at the time was called “natural philosophy.”

Anaximenes believed air was divine in the same way that his teacher Anaximander believed his fundamental principle the apieron was divine, and his teacher Thales thought that water was divine. The Greeks believed that which is eternal and in motion, such as air, was divine, had a soul, and therefore was capable of bringing about a living world. This concept of divinity is far from the earlier Greek’s mythological understanding of the world as being ruled by the Olympic Gods. Together in this new and exciting time in Miletus, Greece, these three men were able to think critically and try to account for the worlds origins, elements, and the changes going on around them based on rational principles. This is why they are considered the first philosophers.

With air as his principle along with his theory of change, Anaximenes created an interesting cosmology (“study of the world”). He saw the earth as having been flattened by air into a disk. Evaporated air from the earth turned into fire, creating the heavenly bodies. The earth as well as the sun and moon sat on streams of air. The sun and planets don’t go around the earth in a circle, as his teacher Anaximander believed, but instead they go around the way you can turn a baseball cap around your head. Night, therefore, occurred when the sun would go behind parts of the earth that would temporarily block it.

The Greeks saw the weather (i.e. meteorology) and the planets (i.e. astronomy) as intimately connected. Therefore, for Anaxamenes, lightning and thunder no longer came from Zeus, but rather were the result of wind breaking through the clouds. He thought earthquakes were the result of the earth cracking because of too much or a lack of moisture. Anaximenes is credited with correctly recognizing that rainbows are formed when the suns rays fall on the clouds, as well as that the moon is bright because it reflects the sun. By identifying hot with dry and cold with wet, he further enhanced the Greeks’ understanding of the relationship between an element’s state and it’s properties.

Anaximenes theory would come to influence many other Greek philosophers. His theory of change was further developed by Heraclitus, while also subject to the criticisms of Parmenides. Anaxagoras, Melissus and Plato all appreciated the simplicity of this model of how the world came to be (cosmogony) and how it now changes. Diogenes of Apollonia developed his own monistic theory (a theory of the world which is made up of only one fundamental substance) using air, and Hippocrates would also emphasize air in understanding diseases. Anaximenes’ view that our breath is divine air is also similar to the Hebraic concept of ruach which means both wind and soul, as well as the Chinese concept of qi as breath, or vital energy.