While Anaximenes was the preeminent Milesian philosopher in Ancient Greece, he is often given lower importance than the others in the modern day.

Condensation would make the air denser, turning it into wind, clouds, water, earth, and finally stone.

He also provided early examples of concepts such as natural science, physical change, and scientific writing.

[1][2] Surviving information about the life of Anaximenes is limited, and it comes primarily from what was preserved by Ancient Greek philosophers, particularly Aristotle and Theophrastus.

[1] Anaximenes was likely also taught Homeric epics, Greek mythology, and Orphism, which may have influenced his philosophy through their portrayal of the classical elements.

[4] Anaximenes's apparent instructor, Anaximander, was a Milesian philosopher who proposed that apeiron, an undefined and boundless infinity, is the origin of all things.

[7] According to their writings, each philosopher of the Milesian School was a material monist who sought to discover the arche (Ancient Greek: wikt:ἀρχή, lit.

Philosophers have concluded that Anaximenes seems to have based his conclusions on naturally observable phenomena in the water cycle: the processes of rarefaction and condensation.

He derived this belief from the fact that one's breath is warm when the mouth is wide while it is cold when the air is compressed through the lips.

[19][13] Anaximenes also likened the soul to air, describing it as something that is driven by breath and wills humans to act as they do.

[22] From this, Anaximenes suggested that everything, whether it be an individual soul or the entire world, operates under the same principles in which things are held together and guided by the air.

This is most prominently indicated in the weather and the seasons, which alternate between hot and cold, dry and wet, or light and dark.

[15][17] Anaximenes believed that the universe was initially made entirely of air and that liquids and solids were then produced from it through condensation.

[26] Earthquakes, he asserted, were the result of alternating drying and wetting of the earth, causing it to undergo a cycle of splitting and swelling.

[37][38] Anaximander instead invoked metaphors of justice and retribution to describe change, and he made direct appeals to deities and the divine in support of his beliefs.

[42] Further details of Anaximenes's life and philosophical views are obscure, as none of his work has been preserved, and he is only known through fragments and interpretations of him made by later writers and polemicists.

[43] Early medical practice developed ideas similar to Anaximenes, proposing that air was the basis of health in that it both provides life and carries disease.

[40] Anaximenes's conception of air has been likened to the atoms and subatomic particles that make up all substances through their quantitative organization.

[20] His understanding of physical properties as quantitative differences that applied at individual and universal scales became foundational ideas in the development of natural science.

[44][17] He was the first philosopher to analogize his philosophy in practical terms, comparing the functions of the world to behaviors that can be observed in common activities.

[47] Plato referenced the concept of air as the cause of thought in the Phaedo, rejecting it with the argument that one's physical state does not determine their fate.

[5] In his Metaphysics, Aristotle characterized Anaximenes and his predecessors as monists, those who believe that all things are composed of a single substance.

[5] Other ancient philosophers who analyzed the work of Anaximenes include Simplicius, Aetius, Hippolytus, and Plutarch.

[51] Werner Heisenberg said that the philosophy of Anaximenes caused a setback in scientific understanding, as it moved analysis away from physical properties themselves.

[40] Karl Popper suggested that Anaximenes and Anaximander developed a philosophy of rationalist critique, allowing criticism of one's teacher, that was not revived until the Renaissance.