Anaxagoras of Clazomenae (c. 500–428 BCE)

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(c. 500428 BCE)

One of the leading philosophers of the fifth century BCE, Anaxagoras continued the cosmological style of philosophy begun in Miletus in the preceding century. Born in Clazomenae in Asia Minor around 500, he came to Athens and spent thirty years there, enjoying access to intellectual circles through his friendship with Pericles. Two alternate accounts of his dates in Athens are available: either he came around 480 and stayed until 450, or he came around 460 and stayed until 430. Because his name is associated with a meteor that fell near Aegospotami around 467, and his theory of the Nile floods was known to Aeschylus (d. 456), it appears that his work was well known already in the 460s, supporting an early date at least for his philosophical activity. Anaxagoras is said to have fled Athens to avoid prosecution on a charge of impiety, and he finished his days in Lampsacus in northern Greece, where he died in 428. He wrote a book that was well-known in Athens in the late fifth century BCE and was available until the sixth century CE. About twenty fragments of the book survive, describing some key points of his theory. Although Anaxagoras wrote in simple Ionic prose, many details of his theory remain obscure and controversial.

Like most natural philosophers of his time, Anaxagoras tells how the world arose from a primeval chaos. Initially, all things (kinds of matter, presumably) were mixed together to such an extent that nothing was differentiated. But Mind (Nous ) caused a whirling motion to start, which caused different materials to separate out, as in a centrifuge, leading to the articulation of the cosmos. At the center of the cosmos is a flat earth, surrounded by stony bodies in the heavens carried around by the cosmic vortex motion. The sun is a hot stone and the moon an earthy body. This cosmogony broadly follows the pattern set by Anaximander, and it shows the influence of Anaximenes in some details. In making the heavenly bodies spherical bodies, Anaxagoras may be following the pattern of Parmenides's cosmology.

Anaxagoras's Principles

What is innovative about Anaxagoras's theory is not the sequence of his cosmogony, but the principles on which he bases it. In the first place, he adheres to a principle of No Becomingpreviously articulated by Parmenidesaccording to which nothing can come to be out of what is not. But whereas Parmenides seems to have meant this principle as a grounds for ruling out cosmological theories, Anaxagoras uses it as a restriction on what kind of explanation is allowed. Second, Anaxagoras follows a principle of Universal Mixture, which he states repeatedly, to the effect that everything is mixed with everything. There has been much controversy among interpreters about what the domain of "everything," in its two occurrences, is. Whatever the precise interpretation, the principle clearly applies to the primeval chaos insofar as all stuffs seem to be thoroughly mixed; but Anaxagoras maintains that even when the separation process takes over, some quantity of every stuff remains mixed with any given stuff. Third, Anaxagoras holds to a principle of Infinite Divisibility, according to which there are no minimal particles of matterno atoms. Finally, Anaxagoras accepts a principle of Predominance, such that any stretch of matter manifests the properties of whatever stuff it has the largest quantity. Thus, if there is more water than salt in a mixture, people perceive it to be water; if more salt than water, they then perceive it to be salt.

It is generally agreed that the point of Anaxagoras's principles is to account for change with the least allowance for novelty: When one thing seems to change into another thing, the second does not arise out of nothing, but was already present (if in a lower concentration). Thus there is change, but no radical coming to be out of what is nota possibility forbidden by Parmenides. What is less clear is whether Anaxagoras succeeds in formulating a coherent account of change. Whether he succeeds depends in large measure on how one interprets the details of his theories of matter and change, which will be discussed briefly below.


A fifth principle that is often attributed to Anaxagoras is Homoiomereity, using a Greek term of Aristotle's that designates a stuff in which the parts are like the whole. Thus if one divides a quantity of water in half, one gets two (smaller) quantities of water; but if one divides a chair in half one does not get two chairs. The former sort of being is called homoiomerous. Aristotle calls Anaxagoras's basic stuffs homoiomeries, but it is not clear whether he intends to say of them that they have the property of homoiomereity; or whether he simply wishes to denote things that in Aristotle's own system are homoiomeries (e.g., flesh and bone), whatever their properties for Anaxagoras. In any case, neither the term nor the property is found in the fragments of Anaxagorasexcept as the property is applied to Mind, which does not behave like a physical element.

Another controversy concerns the relationship between stuffs and contraries, or qualities in general. Anaxagoras mentions qualities such as hot and cold alongside stuffs such as earth (fr. 4) and maintains that contrary qualities cannot be cut off from each other (fr. 8). Does Anaxagoras recognize a strong categorial difference between stuffs and qualities, and if so, what is their relationship? According to one interpretation, the stuffs are composed of qualities, such that different amounts of hot, cold, wet, dry, and so on, combine to constitute different stuffs. Thus Universal Mixture signifies that every stuff is potentially in every stuff because by changing the ratios of qualities one can produce other results. On this view Anaxagoras is a reductionist who reduces stuffs to qualities. Defenders of this view have sometimes claimed that only on this interpretation can Anaxagoras's principles be rendered consistent. Yet, other interpreters have shown that his principles can be made consistent without reducing stuffs to qualities. Critics of the reductionist view see Anaxagoras's stuffs as elemental bodies. Qualities could be either stuffs in their own right, or simply properties that happen to describe certain stuffs.

Another controversial question is the meaning of the seeds Anaxagoras refers to in fr. 4 as being part of the original mixture. Are these biological seeds, as some interpreters hold, from which the first plants and animals grew? Or are they structural principles generally, to account for the presence of shapes and structures which emerge from the formless mixture (perhaps including, but not confined to, shapes of plants and animals)? Or are they small particles of a given stuff that are present as starting points for the growth of that given stuff? (A number of other hypotheses have also been advanced.) On many of these hypotheses, at least, no stretch of matter could be homoiomerous, for it would contain seeds having a different composition from the whole. Anaxagoras does not say enough about seeds to allow scholars to make a clear determination in favor of one of these hypotheses.

In another difficult saying in fr. 4, Anaxagoras talks about an alternative to "our" world. But is his statement merely counterfactual, or does he hold that there are other worlds, like the atomists; or worlds within worlds, as among Leibniz's monads; or repeating worlds, as does Empedocles? There is no more consensus on this question than on the other controversies mentioned.

Mind and Knowledge

One of Anaxagoras's most interesting and innovative theories is his philosophy of mind. As has been shown, Anaxagoras makes mind responsible for the beginning of the cosmic vortex. He says that mind is "boundless, autonomous, and mixed with no object" (fr. 12). If it were not "by itself" it would be mixed with everything, by Universal Mixture, which would hinder it from ruling things. As it is, mind is "the finest of all objects and the purest, and it exercises complete oversight over everything and prevails above all" (fr. 12). Mind is present in some things, namely those things that have soul, but it does not mix with them. Thus mind is not immaterial, but it is not material in the same way as the stuffs are. It exercises control over the stuffs of the world and comprehends all things. Anaxagoras's theory suggests a dualism of mind and matter, though it is not nearly as radical as Descartes's dualism. In any case, Anaxagoras is the first philosopher to recognize mind as a distinct reality alongside physical entities. In cosmology, Anaxagoras is the first philosopher to support creationisminvolving not a creation ex nihilo, to be sure, but an organization of preexisting elements by an intelligent agency distinct from those elements.

Anaxagoras accounts for sense perception as the effect of opposite qualities on opposites; thus one perceives hot by cold and wet by dry. He observes that because of the weakness of the senses people are not able to perceive the truth (fr. 21). But, on the positive side, "Appearances are a vision of the invisible" (fr. 21a). A serious philosophical problem for Anaxagoras is how humans can have knowledge at all. Because everything is mixed in everything, if I perceive something as water, I may infer that it is composed of water, and salt, and every other kind of stuff. But how can I say that I know the body before me as water if I have to analyze it as, among other things, water, and the water that I analyze it into is a theoretical entity I do not perceive? I seem to be involved in a regress that keeps me from knowing anything, except in a purely hypothetical way, in which everything has exactly the same components (all the stuffs there are), all of which are perceptually inaccessible to me.

Here, fr. 21a (just cited) provides a possible way out of the problem. People know by an inference to the best (or only possible) explanation that there are countless basic stuffs in the world. Further, they are acquainted with those stuffs by their manifestations to sense experience. Because when some stuff predominates, it gives its character to the whole body it predominates in, they can infer the character of, for instance, elemental water from the character of phenomenal water in bodies of water they encounter. Similarly, people can infer the character of all other basic stuffs from their appearances, because, by hypothesis, the basic stuffs are like their phenomenal counterparts. People cannot give an adequate verbal definition of water, but they can give an ostensive definition of it. Thus they know the structure of reality by theory, but the content of reality by experience. This same sort of strategy appears to have appealed to Democritus, who approved of Anaxagoras's statement in B21a and applied it to his atoms (for a limited range of properties).

Physical Theory

Though in some ways conventional, Anaxagoras's physical theories made some important advances. Like most of his predecessors, Anaxagoras envisioned a flat earth at the center of the circling heavens; the earth is held in place by air pressure, and the solstices of the sun are caused by winds in the heavens. He explained the annual floods of the Nile as the result of melting snows in southern Africa (the Nile is in fact fed by melting snows, but the floods are caused by monsoon rains), a view cited by Aeschylus, Sophocles, and Euripides, and criticized by Herodotus. He gave an essentially correct explanation of hail. His view that the heavenly bodies are earthy or stony was probably novel, and he believed that invisible stones were also carried about aloft with the vortexin effect, he posited asteroids. When a large meteor fell at Aegospotami, Anaxagoras was given credit for predicting it, and henceforth meteors were included among data to be explained by cosmological theories. He gave the first correct explanation of solar and lunar eclipses (perhaps inspired by Parmenides's recognition that the moon gets its light from the sun), a feat that Aristotle regarded as a paradigm of scientific discovery. He also correctly hypothesized that the moon had mountains and valleys on its surface. In his physical theory he was followed by Archelaus of Athens, and in his teleological tendencies by Diogenes of Apollonia.

After Anaxagoras, natural philosophers mostly accepted his theory of eclipses and his view of heavenly bodies as spherical solid bodies. Though his astronomy was influential among intellectuals, it clashed with popular religious views according to which the sun and moon were gods, and led to an indictment of impiety in Athens. It was the sort of theory that Plato criticized in the Laws as leading to atheism. Anaxagoras presumably would reply that his views offered grounds for a more enlightened religion than those based on worshiping forces of nature.

Plato saw one of Anaxagoras's views as offering a new approach to cosmology. If Mind ordered everything with a view to the best, then philosophers should be able to explain the structure of the cosmos on the basis not of how it arose from a primeval chaos, but how it manifests order and value. Plato reports that Anaxagoras's book was disappointing because it failed to exploit this insight, and Aristotle agrees. In fact, Anaxagoras used the same style of explanation as other pre-Socratics stressing the natural capacities of different kinds of matter. But Plato later used Anaxagoras's insight to construct the cosmos on teleological principles in his Timaeus. In a sense, then, Anaxagoras provided the impulse for the rational cosmologies of Plato and Aristotle that dominated ancient and medieval thought. He was the first philosopher to make his home in Athens, and also the first to offend the Athenian people. Through the Athenian philosophical tradition he had a lasting influence.

See also Anaximander; Aristotle; Atomism; Cosmology; Descartes, René; Diogenes of Apollonia; Dualism in the Philosophy of Mind; Empedocles; Leucippus and Democritus; Nous; Parmenides of Elea; Philosophy of Mind; Plato; Pre-Socratic Philosophy; Sensa.


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Daniel W. Graham (2005)

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Anaxagoras of Clazomenae (c. 500–428 BCE)

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