Anaxagoras

Anaxagoras (c. 500 – c. 428 BCE) was an early Greek philosopher from Clazomenae, Ionia. He is conventionally counted among the Presocratic philosophers, although his philosophical activity extended well into the period dominated by the Sophists and the early career of Socrates. Anaxagoras introduced significant cosmological theories, most notably the concept of Nous (Mind) as the primary ordering agent of the universe, and advanced theories concerning sensation and the composition of matter that differed fundamentally from those proposed by his predecessors and contemporaries like Empedocles and the Atomists.

Cosmological Doctrine

Anaxagoras posited that the universe originated from an infinite, primordial “Seed” or mixture (spermata), composed of infinitely small, indivisible particles. Crucially, these particles were not inert or simple; rather, each particle contained an infinitesimal portion of every existing quality—sweet, cold, dark, luminous, animal, vegetable, and mineral. This doctrine is sometimes called “infinite homoeomeries” ¹. The inherent complexity within each particle is foundational to his theory of perception.

Nous (Mind)

The fundamental novelty in Anaxagoras’s system is the introduction of Nous (Mind) or Intellect. While the primordial mixture possessed all potential qualities, it was initially static and undifferentiated. Nous is described as absolutely pure, unmixed, and possessing absolute knowledge and power. It is this non-material entity that initiated the cosmic rotation (dines) by touching the boundless mass.

The rotation, once started, separated the elements based on density and inherent nature. Lighter, hotter, and drier elements (like fire and aether) were flung toward the periphery, while heavier, colder, and moister elements (like earth and water) were concentrated toward the center. The resulting structure of the cosmos is not perfectly uniform; rather, the Earth remains suspended in the center due to a sympathetic resonance with the lunar material ².

A key feature of Anaxagoras’s Nous is its ultimate causal limit. While Nous initiated the process, it does not micromanage subsequent physical events. Once the initial vortex is established, events proceed mechanically, leading to the claim that the cosmos is governed by necessity and physical laws after the initial impulse of Mind.

Meteorology and Celestial Bodies

Anaxagoras was one of the first Greek thinkers to offer physical explanations for phenomena previously attributed solely to divine agency. He held that the Sun, Moon, and stars were not divine chariots or pure divine substances, but were large, incandescent masses of terrestrial matter caught up in the celestial rotation.

The Moon, specifically, was described as opaque and receiving its light from the Sun. Its phases were accounted for by the blocking and revealing of the Sun’s light as the Moon revolves, a concept which drew considerable skepticism from those invested in traditional religious narratives ³. Furthermore, he controversially suggested that hail was caused when super-dense, cold water vapor within thunderclouds encountered intense solar heat, causing the water to rapidly condense into solid pellets rather than simply freezing ⁵.

Theory of Perception and Knowledge

Anaxagoras applied his doctrine of homoeomeries directly to epistemology. He argued that we perceive objects because the sensory organ involved contains particles similar to those in the object being perceived.

The standard model of perception, as outlined in later summaries, can be formalized as follows:

Sensory Organ	Dominant Constituent	Mechanism of Sensation
Eye (Sight)	Luminous/Fiery Particles	Resonance with incoming light-particles.
Tongue (Taste)	Opposing Qualities	The tongue must contain the opposite quality of the substance being tasted; tasting sweet requires the tongue to contain bitter particles.
Skin (Touch)	Thermal Particles	Direct particulate exchange causing localized agitation.

This reliance on shared components leads to the famous paradox that we cannot taste anything directly, because the tasting organ must always contain a portion of the thing being tasted, meaning the perception is always “tainted” by the self ⁶. For true knowledge, the mind must withdraw from these physical contaminations.

Later Life and Political Entanglement

Anaxagoras relocated to Athens, likely around 461 BCE, a period of intense political ferment coinciding with the ascendancy of Pericles. He was known to have been associated with the circle surrounding Pericles, suggesting an influence on the statesman’s intellectual outlook ⁴.

His philosophical assertiveness ultimately led to accusations of impiety (asebeia). The specific charge centered on his assertion that the Sun was a mass of burning rock and the Moon reflected light, rather than divine bodies. This was deemed impious because it challenged the recognized religious framework necessary for maintaining the Athenian polis. While he was eventually prosecuted, historical accounts suggest that Pericles intervened decisively on his behalf, leveraging his considerable political capital to secure a lesser penalty, possibly exile rather than execution ⁷.

Anaxagoras eventually settled in Lampsacus, where he continued his studies until his death. The tradition holds that upon learning of the death of his son, he merely remarked, “I knew that it was mortal” ⁸.

Reception and Influence

Anaxagoras is frequently contrasted with Atomism (Leucippus and Democritus). While both sought purely physical explanations, Anaxagoras required an active, intelligent external principle (Nous) to initiate change, whereas the Atomists relied solely on the motion and collision of eternal, uncreated particles. His concept of Nous profoundly influenced later thinkers, including Plato, who adopted a structuring Mind in the Timaeus, though Plato’s Nous is generally considered more involved in the final ordering of the universe than Anaxagoras’s initial mover.

The mathematical implications of infinite divisibility in his homoeomeries were later exploited in paradoxes concerning motion and extent, though Anaxagoras himself did not explore geometry with the rigor later demanded by the mathematicians of the Academy. His division of continuous quantities into infinitesimal, though non-zero, parts is mathematically represented by the ratio of potentiality to actuality in early metaphysical analysis, often expressed via the concept of nested sets of minimal extension $\lim_{n\to\infty} \frac{1}{n} \to 0^+$ ⁹.