By the time of the third of the great Milesian philosophers, Anaximenes, an established tradition was in place, which he consciously expressed. Virtually nothing is known of his life except that he lived in Miletus, was probably somewhat younger than Anaximander , was either the latter’s pupil or anyway under his influence, and wrote a book. This book, like Anaximander’s, seems to have contained, along with a version of material monism, a protoscientific description of the universe and its workings.
Philosophically, Anaximenes’ work, like Anaximander’s, is represented by only one extant fragment in his own words or something close to them; these words are contained within a passage by the late author Aetius:
Anaximenes, son of Eurystratus, of Miletus, declared that air is the principle [arche -] of existing things; for from it all things come-to-be and into it they are again dissolved. As our soul, he says, being air, holds us together and controls us, so does wind (or breath) and air enclose the whole world. (DK 13B2)
At first sight Anaximenes seems to have taken a step back from the more abstract conception of Anaximander toward the more concrete and myth-based conception of Thales. But he was not without his reasons. According to Cicero (De Nat. Deor.I..), Anaximenes called air “the divine,” and he may have been influenced by the traditional belief that air, or breath, is soul-stuff, that it is the carrier of consciousness . The universe, on that account, is a pantheos which has the divine air element as its breath-soul. The Pythagoreans, not long after, would teach similarly that the universe is a living organism which breathes one vast breath. The concept of the pantheos, in other words, outlasted the specifically anthropomorphic descriptions of the Macranthropus; even when viewed as a contraption of wheels and gears, the universe was regarded as a living god .
The most important aspect of Anaximenes’ innovation was his theory that changes in the one substance are produced by a process of condensation and rarefaction. Thales’ watery One may have produced on the analogy with chemical changes of state; Anaximander’s One, by separating out opposites in balanced and balancing procedures. Anaximenes’ air-substrate produces the variety of forms by condensing and rarefying itself. Air rarefied becomes fire, and produces the fiery objects, sun and stars; air condensed becomes mist or cloud, then precipitates out of the cloud state into the water state as rain, then becomes further condensed as earth, then finally becomes compressed into minerals. The conception is of great importance in several ways. First of all it tacitly contains the message, which Heraclitus would derive from it, that the unity of the world is the unity of a vast process happening; it is not primarily a type of matter that is the substrate, it is the process by which matter is being transformed through various appearances. Air is declared the essential type (or stage) of matter because, as the soul , it is somehow the ruling principle, from which the motive force arises. In addition, Anaximenes’ model is based to a certain extent on the observation of cyclical processes in nature such as precipitation and evaporation. Such a basis in natural science may have been present already in Thales, but was definitely present in Anaximenes. Finally, the concept of condensation and rarefaction contains implicitly the seeds of atomism because it posits material change at an infrasensory level.
In India as early as the Atharva Veda (X..) the wind was regarded as the breath of Skambha, the “Substrate,” which supports the entire universe. Indeed, the “pa-dna theory,” or theory that air is the material substrate, is prominent in early Indian thought. Pra-na, the Sanskrit equivalent of Greek pneuma , “breath, air, soul,” appeared in the Atharva Vedaas a ruling cosmic principle. “Air, in whose power is this All, who is the Lord of all, on whom all is based … in air is what has been and what is to be; everything is based on air” (AVII.).
The Chandogya Upanishad develops a model still closer to that of Anaximenes. As he called air “the encompassing,” the Upanishad says: “Air is the absorbent, for when a fire goes out, it goes into the air. When the sun sets, it goes into the air, and when the moon sets it goes into the air. When water dries up it goes into the air. For air, indeed, absorbs them all” (Chandogya UpanishadIV..–2). The Brhadaranyaka Upanishad states that “from prana the sun rises and in prana it sets” (Brhadaranyaka Upanishad I..). Similarly the Kaus.itaki Upanishad, also an early one, declares that all things die into the wind and rise up from it again (Kausitaki Upanishad II.). Yajnavalkya teaches a close analogue to the doctrine of a universal breath that contains all individual breaths: “Air,” he says, “is the separate individuals, and air is the totality of all individuals” (BUIII..).
The description of the world process on the analogy of condensation and rarefaction also seems to be enunciated in the Upanishads. The mechanism is not specifically identified, but the series of transformations of matter seems based, as in Anaximenes, on increasing density. In both the Chandogyaand Brhadaranyaka Upanishads, in what is called the Doctrine of the Five Fires, the process from element to element or state to state proceeds “from space into air, from air into rain, from rain into the earth” (BUVI..), much as Anaximenes’ progression goes from air to mist to rain to earth.
Finally, it seems that all the metaphysical elements of Milesian monism were present in Indian thought, many of them at a considerably earlier age than their appearance in Greece. An important difference must be observed, however, between the Greek and Indian modes of thought about One and Many. In the Upanishads the concept of brahman stands more or less as the beginning and the end of thought. Insofar as its ramifications are spelled out, they are ethical ones. But Anaximander’s book is known to have included, alongside its elucidation of the Infinite, a complex nuts-and-bolts description of the working of the cosmic mechanisms, in line with his study of astronomy and his use of visual models such as the map and the celestial globe. His description of the cosmos was an eclectic synthesis of elements borrowed from Mesopotamian, Egyptian, and Persian sources. His statement, for example, that the earth is concave like a bowl is associated with the Mesopotamian world-map in which the circular earth is surrounded by seven mountains, and with the related Egyptian belief in the “surrounding mountain” that rings the earth. His vision of wheels within wheels is echoed in the vision of his contemporary Ezekiel, who saw cherubs turning on concentric wheels about the throne of god in the sky; it represents a general Near Eastern conception of the heavens, probably Mesopotamian in origin, that would recur in both Parmenides ’ and Plato’s visions of the cosmic workings. The order in which Anaximander places the celestial bodies—with the stars nearest the earth, then the moon, then the sun—is eccentric in either Babylon or Greece but normal in the Persian Avesta, which, at some remove, may be its source.
Indian thinkers of the Middle Vedic and Upanishadic periods may have had access to similar sources, but they did not produce from them mechanical models of world process. The Milesians, more so than their Indian peers, are regarded as protoscientists —people who wanted to believe that the world was certifiably knowable and to devise a systematic method with which to know it. In keeping with the intuitionist background to their emerging profession, they approached the project also as quasi-mystics expressing primal wonder at the existence of the universe. Their attempt to go beyond mythological ways of explaining the universe, expressed as it was in mechanical models as well as metaphysical insights, bore as much significance for the development of science as of philosophy.