Discover the philosophy of Anaximenes, the ancient Greek thinker from Miletus who proposed air as the fundamental substance of reality. Learn how he explained change through rarefaction and condensation, introduced testable experiments, linked microcosm and macrocosm, and used analogy in reasoning.

Table of Contents

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Anaximenes – Time and Place

• Anaximenes was the third famous philosopher from the city of Miletus.
• He lived around 545 BC and was younger than his teacher Anaximander.
• Exact birth and death dates are unknown.
• He wrote a book, but the original text has been lost over time.
• Some quotes from his work survive in the writings of later authors.
• His writing style was known to be serious and strict.

Summary

Anaximenes was a key philosopher from ancient Miletus, active around 545 BC. A student of Anaximander, he was younger in age and carried forward the philosophical tradition. His original book no longer exists, but a few of his quotes are preserved in later writings, showing his serious and structured style.

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Anaximenes’ Criticism of Anaximander’s Theory

• Both Anaximenes and Anaximander asked the same question: What is the basic substance that forms the foundation of all reality?
• Anaximander answered: Apeiron (Boundless) — infinite, undefinable, without specific qualities.
• Anaximenes rejected this answer, saying:
  • A valid answer must be clear and definable.
  • If the primary substance cannot be defined or described, it is not a real answer.
• Later historians also saw two main problems in Anaximander’s Apeiron:
  1. Something can only exist if it has particular properties to identify it — Apeiron has none.
  2. Apeiron cannot be called “one substance” because it is like a bag containing many different things, not a single entity.
• Anaximenes believed Apeiron was poorly defined and logically contradictory, so he began searching for a better explanation.

Summary

Anaximenes disagreed with his teacher Anaximander’s idea of Apeiron as the primary substance of reality. He argued that something without specific qualities cannot exist or be defined, and that Apeiron’s description was contradictory. To him, it was not truly one substance but a container of many things. This led Anaximenes to look for a clearer and more logical answer to the question of the universe’s foundation.

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Anaximenes’ Theory – Air as the Basic Substance

• Anaximenes said the fundamental reality is Air (Greek: Aer — meaning mist, vapour, or air).
• He gave four main reasons why air is the basic substance of the universe:
  1. Most Pervasive: Air is everywhere, even inside water.
  2. Essential for Life: No living being — humans, animals, plants — can survive without air; even fire needs air to burn.
  3. Self-Supporting: Air does not need any support to stay in place, unlike water or solid objects. He believed the Earth floats on air like a leaf, not on water as Thales suggested.
  4. Like a Soul: Air is linked to life — as long as we breathe, we live; when breathing stops, life ends.
• Anaximenes also said that the motion of air is eternal and has always existed.

Summary

Anaximenes proposed that air is the primary substance from which everything is made. He argued that air is everywhere, essential for all forms of life, self-supporting, and directly connected to the idea of a soul. To him, air’s motion is eternal, making it the foundation of all reality.

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Anaximenes on the Problem of Change – How Air Becomes Everything

• Main question: How does the first principle, Air, change into different things?
• Key idea: Change happens when the density of air increases or decreases.
• Two processes explain this:
  1. Rarefaction – air expands, density decreases.
  2. Condensation – air compresses, density increases.
• Transformation sequence:
  • Expansion: Air → Steam → Smoke → Fire.
  • Compression: Air → Mist → Water → Mud/Dirt → Stone.
• Experiment by Anaximenes:
  • Blow with your mouth closed → air is cooler (condensed).
  • Blow with your mouth open → air is warmer (expanded).
• Key principle: Quality depends on quantity.
  • Qualitative change (different states or types) happens because of quantitative change (density).
  • Example:
    • Water molecules densely packed → Ice (solid).
    • Loosely packed → Liquid water.
    • Very spread out → Steam (gas).
  • Football with more air molecules → hard; fewer molecules → soft.
• Application to the universe:
  • Fire and stone have different qualities, but both are made of air — only their density differs.
• Difference from Anaximander:
  • Anaximander’s Apeiron is a source from which things come but are not made of it (like cloth from a box).
  • Anaximenes’ Air is a material substance from which everything is directly made (like a plastic item made from plastic).

Summary

Anaximenes explained change by saying that all things are made from air, which transforms through rarefaction and condensation. As air expands or compresses, its density changes, creating different materials — from fire to stone. He introduced the important idea that quality depends on quantity: the nature of something is determined by how much of the primary substance it contains. Unlike Anaximander, who saw his principle as a source but not a material, Anaximenes believed everything is literally made of air.

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Other Interesting Ideas of Anaximenes

• Flat Earth theory: Anaximenes believed the Earth is flat and floats on air, like a leaf floating in the air.
• Support by Air:
  • Unlike Thales, who said water supports the Earth, Anaximenes argued water is not self-supporting, but air is.
• Nature of the Sun, Moon, and Stars:
  • They are made of refined air — essentially fire.
  • Like the Earth, they are also flat and supported by air.
• Movement of the Sun:
  • The Sun does not go beneath the Earth.
  • At sunset, it moves sideways around the Earth and returns to its starting point.

Summary

Anaximenes expanded his philosophy to include ideas about the shape and structure of the Earth and the heavens. He described the Earth as flat, floating on air, and believed the Sun, Moon, and stars were made of refined air (fire) and also flat. His model explained day and night by suggesting the Sun circles sideways around the Earth rather than going underneath it.

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Anaximenes — Significance & Key Contributions (Revision Notes)

• Conceptual clarity:
  • A good answer must be clear and definable.
  • Anaximenes rejected Anaximander’s Apeiron because it was vague.
  • He insisted philosophy should give clear, concrete claims.
• Direct solution to the problem of change:
  • He explained change by density change in Air (rarefaction = expand, condensation = compress).
  • This gives a simple mechanism for how one thing becomes another (air → steam/smoke/fire or air → mist/water/mud/stone).
• Experiment and verification:
  • He used a simple test you can try: blow with mouth closed (cooler air → condensed) vs open (warmer air → rarefied).
  • His claims are testable — an important step toward empirical thinking.
• Quantitative description:
  • He argued that reality can be explained by numbers (how much, how dense, how hot).
  • Quality (solid/liquid/gas, hard/soft, fire/stone) depends on quantity (density, amount).
  • Examples of measurable properties: mass, volume, density, temperature, speed.
• Microcosm — Macrocosm connection:
  • Small systems (microcosm) reflect large systems (macrocosm).
  • Example comparisons: neurons ↔ galaxies, ant colony ↔ city, breath ↔ cosmic breath.
  • His idea: the same basic principle (air) acts in both human life and the whole universe.

Argument by Analogy (Method and Limits)

• Definition (plain): If two things are similar in some ways, we sometimes assume they are similar in other ways.
• Examples:
  • Thales: wood floats on water → Earth floats on water (analogy).
  • Anaximenes: breath supports life → cosmic breath supports the world.
  • Watch → complex, World → complex ⇒ both may have a maker (watchmaker argument).
• Logical form: If X is P and Q, and Y is P, infer Y is Q.
  • Watch is complex, so it has a maker.
  • World is complex.
  • So, world must have a maker.
• Caution: Analogy is a weak proof but can suggest ideas. Sometimes it works (e.g., Thales used shadow of a stick to measure pyramid height).

Summary

Anaximenes made philosophy more concrete. He argued that air, changing by compression and expansion, becomes all things. He insisted on clear ideas, offered a testable experiment, and tried to explain the world with measurable quantities. He also connected small-scale experience to the whole universe and used analogy to reason — a useful method but not a strong proof.