So far we can recognize Parmenides as offering a significant alternative to the quasi-scientific theories of his predecessors: a theory in which the world is composed of changeless elements that combine in compounds. It turns out that the insight he developed offered the foundation of the true account of substances arrived at scientifically in the nineteenth century CE. The future development of science was, of course, unknown and unknowable to the thinkers of earlier centuries, and so could not, of itself, have motivated a major shift of thinking about the composition and structure of the world.
But there is another contribution Parmenides made in his cosmology which was, as we shall see, immediately evident to his contemporaries and successors. That came in the realm of astronomy and cosmology. In retrospect, we can identify three breakthrough insights he laid out in his account of the cosmos. First, he identified the Morning Star with the Evening Star. Second, he recognized for the first time that the moon shines by reflecting light from the sun. Third, he was the first thinker to assign to the Earth a spherical shape. All three of these insights should count as scientific discoveries—despite the fact that many post-modern thinkers bristle at the thought of there being such a thing as scientific progress, much less progress marked by milestones such as discoveries.[1]
Up until the time of Parmenides, the Ionian philosophers had shown a great interest in astronomy and cosmology, and it is fair to say that most of them had seen their primary role as being the developers of a rational theory of the cosmos. Furthermore, the first Western philosophers had shown a great deal of ingenuity in explaining the cosmos. They had distinguished between basic kinds of stuff, such as earth, water, and fire; they had identified stuffs that might have been ignored by less observant thinkers, such as air. They have developed stuffs into a series of more or less dense stuffs, such as that developed by Anaximenes. They had thought deeply about the causes of motion and change in the world, the origin and status of the heavenly bodies, the origins of life, and of the human race. They had appealed to fossil evidence. They had attempted to explain the seas and the water cycle, rivers, weather patterns, storms, seasons, earthquakes, and even distant local events such as the Nile floods. They had marvelously inventive accounts of how the world arose and how it functioned.
But the early philosophers had never actually explained anything correctly in such a way that we could, at least in retrospect, say that they had discovered anything. In fact, this was a kind of judgment of the empirical failure of all Presocratic philosophy that has been a part of textbooks and monographs in the history of science.[2]
Parmenides changed the face of inquiry into nature forever by making irreversible advances. Unfortunately, his contributions have consistently been ignored or trivialized by scholars, who have focused on his disavowals of cosmology rather than his contributions. Let us look at the latter.
1.5.3.1 The Morning Star is the Evening Star
The concept of a planet is fuzzy in early Greek thought. There is little discussion of them in at least our extant fragments and testimonies. They are not named or counted or described in any detail. The one planet that is highly visible is Venus. It sometimes appears before sunset in the west and sets after the sun; it sometimes appears before sunrise in the east, rising before the sun. When the sun is high in the sky, the planet is invisible because of the brightness of the sunlight. The ancient Greeks and Romans identified it as two planets: the Morning Star, rising in the morning, and the Evening Star setting at night. Each one disappeared for long periods, and the two were never seen on the same day.
Parmenides, apparently focusing on the “two” stars’ position either to the left (east) of the sun or to the right (west) of it, recognized, and their approaches and departures from the position of the sun, recognized that there were one body traveling always in the vicinity of the sun. In fact, Parmenides’ identification of the Morning Star and the Evening Star was a discovery only for the Greek world. Babylonian astronomers—or astrologers, for that was their focus and motivation—had recognized the identity of the two apparitions about a millennium earlier. But the fact that the Greeks did not know this indicates that there was little communication between the Middle East and the Hellenic world, at least in the realm of astronomy. For one could not even read Babylonian almanacs and star charts without knowing that the Morning Star was the Evening Star—both being appearances of the planet Ishtar.[3]
We also might note that the Ionian philosophers from Miletus, Ephesus, and Clazomenae, all on the Aegean coast of Asia Minor and in close proximity to the Persian Empire and its predecessors, had failed to learn of the identity of the “two” stars. Parmenides, who lived far away in southern Italy was the one who made the connection, writing around the time of the Persian War, when communication with the East would have been most difficult.
1.5.3.2 The Moon’s Borrowed Light
Parmenides’ second breakthrough may also have resulted from a close observation of the motions of the sun in connection with other heavenly bodies. Speaking of the moon, he calls it, in his cosmology:
a nocturnal light, shining by borrowed light. (fr. 14)
And he explains it:
ever peering towards the rays of the sun. (fr. 15)
In this carefully constructed account (he makes a wordplay: ‘borrowed light’ allotrion phōs echoes the Homeric phrase ‘foreign man’ allotrios phōs). Fragment 15 points out that the shiny portion of the moon is always facing the sun. The side of the moon nearest the sun is reflecting the sun’s light. Once you see that, you can track the course of the moon, which moves slowly to the left (eastward) about 12⁰ every day. The farther it gets from the sun (the greater the angular distance), the larger it grows, from a thin crescent facing right, to a thick crescent, to a half moon, to a gibbous moon, to a full moon (at 180⁰, when the moon is directly facing the sun), and then it begins to shrink, reversing its phases, now illuminated on its left side as it approaches the rising morning sun. What we are observing is the reflection of sunlight off a dark, spherical body. During the time of the “new moon” the satellite disappears from view, but it still there, just in shadow as it draws near the sun’s location on the ecliptic, with the sun being more distant and behind (above) it as seen from Earth.
Once you see this relationship, it becomes obvious that the sun is the primary light source for the Earth, the moon, and the solar system. But despite the simplicity and elegance of Parmenides’ explanation, no other natural philosopher had come up with this explanation. Only the philosopher who disparaged natural philosophy and was wholly committed to Being in the abstract.
Or was he? Parmenides’ stunning revelation was not the result of armchair excogitations, but of careful observation of the motions of the sun, the moon, presumably of the Morning and Evening Star, and other bodies. His discovery was a leap forward in decoding what had been right in front of our eyes forever. It was a marvel of scientific imagination. Parmenides was the scientist that his predecessors aspired to be without ever quite getting anything right. He connected the dots. He made the inferences. He made the moon a spherical body in low-Earth orbit, the sun a fiery star in upper-Earth orbit.
1.5.3.3 The Earth is a Sphere
In an era when virtually all natural philosophers envisaged the Earth as flat, Parmenides proposed that it was spherical in shape. Before philosophy, Homer and Hesiod have a flat disk-shaped Earth with Ocean flowing around its edges. Thales seems to have seen the Earth as like a raft floating on a vast sea. Anaximander described the Earth as a disk in the likeness of a column drum, referring to the practice of assembling large columns of building by stacking cylindrical blocks. Anaximenes pictured the Earth as thin disk. Xenophanes portrayed it as an infinite plane, with the Earth composed of elemental earth all the way down, and air (with cloudlike heavenly bodies) above the surface all the way up.
Parmenides, by contrast, made the Earth a sphere, and is said to have divided it into five zones, as it is conceived in modern times, with the tropics at the center, temperate zones above and below the tropics, and arctic and antarctic zones near the poles.[4]
We do not have Parmenides’ actual account of the Earth, or so it seems. Recently, Guido Calenda has argued that what is usually taken as Parmenides’ account of the heavens with its stephanai or rings should be understood as a description of the layers and structure of Earth, with a fiery central core.[5] Calenda’s account would resolve a number of tensions in Parmenides’ description of the cosmos.
In any case, there are other known accounts of a spherical Earth in sixth-century BCE cosmologies. But Anaxagoras, writing after Parmenides and in response to him, did criticize the theory that the Earth was spherical, apparently challenging a recent departure from the standard geological model.[6]
In fact, Parmenides’ immediate successors all seem to have rejected his spherical model of the Earth. But in the fourth century BCE, Plato presented spherical Earth (without argument, but with much picturesque detail) in his Phaedo. And Aristotle in his On the Heavens, strongly argued for a spherical Earth, offering both philosophical arguments and sound empirical arguments. That is to say: Aristotle actually proved the existence of a spherical Earth. Mathematical astronomers perhaps before and certainly after Aristotle recognized the value of empirical arguments, with the result that the spherical Earth became a foundational principle of Greek astronomy and Western astronomy forever after.[7]
[1] See D. W. Graham, Science Before Socrates (2013: 7-40).
[2] “[The ideas of the Presocratic philosophers] are the dream children of the speculative thinker in the study intoxicated by the novelty and daring of the new intellectual atmosphere and intent on applying the new methods of thought … in the widest possible field. [The Presocratics] were not, however, primarily scientists, much less astronomers, and observations of celestial phenomena seem to have played a relatively minor role in their thinking.” (D.R. Dicks 1970: 60)
[3] See Hunger and Pingree, Astral Sciences in Mesopotamia (1999: 32-41).
[4] Strabo 2.2.2 = Posidonius fr. 49 Edelstein and Kidd = A44a.
[5] Un universo aperto: la cosmologia di Parmenide e la struttura della terra (Bologna 2017: 61-80).
[6] Martianus Capella 6.590, 592.
[7] See Graham 2013.