In the last episode I was rude about the pre-Socratics and today I intend to be rude about another more noted Ancient Greek philosopher. Quite logically, Socrates (c. 470–399 BCE) follows on from the pre-Socratics, who was followed by his pupil Plato (c. 428–348 BCE), in turn followed by his pupil Aristotle (384–322 BCE). Socrates, Plato, and Aristotle the much-heralded triumvirate of Ancient Greek philosophy. Socrates left no writings and most of what we know about him comes from his pupils Plato and Xenophon. He needn’t bother us here as he wasn’t really interested in natural philosophy. To quote James Hannam:
Late in his [Socrates] life, he was scornful of natural philosophers, not least because the concocted a multiplicity of explanations for phenomena and never agreed on anything. From this, he concluded that none of them knew what they were talking about.[1]
On the other hand, Plato and Aristotle, are the dynamic duo of the history of European science from the fourth century BCE down to the seventeenth century CE, continually weaving in and out of the main narrative. In the case of Plato, viewed rationally there is very little reason why he should have featured in any way prominently in the European history of science; put in modern terminology Plato was not a scientist and his extensive writings contain next to nothing that could be termed science. However, in a couple of his dialogues he includes aspects of cosmology, mostly borrowed from the pre-Socratics, that continued to feature prominently down the centuries, attached to the name Plato.
Plato’s acceptance of mathematics as a medium to describe natural philosophy (although it’s not something that he did himself) in contrast to Aristotle’s rejection of mathematics (because the objects of mathematics were not part of nature) led earlier historians to claim that the mathematization of science, in the early modern period, a prominent feature of the so-called scientific revolution, came about through a change from qualitative Aristotelian philosophy to a neo-Platonic quantitative philosophy. I personally, as I explained in my Renaissance Science series, think there are other more significant drivers of the mathematization of the scientific disciplines in the early modern period, although a more favourable view of Platonic philosophy might have played a minor role in that transition.
Plato’s first significant contribution to the scientific debate was the fact that he provides the earliest extant reference to a spherical earth. Previously, all advanced cultures had assumed that the earth was flat. In the Phaedo, Socrates talking about reading Anaxagoras “I assumed that [Anaxagoras] would begin by informing us whether the Earth is flat or round, and then he’d explain why it had to be that way because that was what was better.”[2] We don’t know who first hypothesised that the world was a sphere, Diogenes Laertius (fl. first half 3rd century CE), writing more than five hundred years later says it was Parmenides but he also said it was Pythagoras, Hesiod, and Anaximander. Remember why I’m sceptical about the things attributed to the pre-Socratics. It is obvious from the Plato quote that a discussion of the hypothesis was already taking place, when he wrote the Phaedo, and it is possible that he had the idea from the Pythagorean, Philolaus (c. 470–c. 385 BCE), but nothing is known for certain. Later in the Phaedo, Socrates says, “In the first place the Earth is spherical and in the centre of the heavens. It needs neither air nor any other such force to keep it from falling. The uniformity of the heavens and the equilibrium of the Earth itself are sufficient to support it.” Although spoken by Socrates it is fairly obvious that Plato is presenting his own view here; a view that adopted by Aristotle would become standard in European cosmology.
The nearest that Plato comes to a scientific text is in his Timaeus, a dialogue on the nature of the world, but like all his other works really a dialogue on ethics. Far from being the, from philosophers, much heralded logos in place of mythos, the Timaeus is a highly mythological tale about the creation of the world by a demiurge or divine craftsman. I’m not going to give an account of the metaphysical twists and turns of the Timaeus and simply filter out those ideas that found its way into mainstream European natural philosophical. One almost bizarre aspect of the dialogue is that although Timaeus gives a fairly detailed explanation of the creation of the Earth by the demiurge, he adds that one “should not look for anything more than a likely story.”
The universe is a sphere with the Earth at its centre. The Earth is not explicitly described as a sphere although it implies that it is a sphere. The demiurge creates the Earth out of Empedocles’ four element–earth, water, air, fire–in varying combinations. For Plato, with his belief in a mathematical world, the four elements now have the forms of four of the regular geometrical solids– Fire-Tetrahedron, Air-Octahedron, Water–Icosahedron, Earth–Cube–a concept that remains in discussion down to at least Kepler.
For Plato, once again borrowing from Empedocles, the planets orbit the Earth, at the centre of the universe, in circular orbits at a uniform speed. Another concept that continued to be largely adhered to down to the seventeenth century. Famously, Galileo in his Dialogo held firm to Plato’s circular orbits, despite the work of Kepler showing the orbits of the planets to be ellipses, which vary in speed.
Adhering to the conditions prescribed by Plato, Eudoxus of Cnidus (c. 480–c. 355 BCE), who is said to have been a student of the Pythagorean Archytas (c. 425–c. 350 BCE) and I member of Plato’s school, the Academy, constructed the earliest known Greek geometrical model of the cosmos, a homocentric or concentric spheres model. Each celestial body has a set of nested spheres with the Earth as a common centre but differing axels. But careful choice of the diameter of the spheres and the position of the axels, Eudoxus was able to create a reasonable model of the seeming irrational movement of the planets using only uniform circular motion.
In most modern reconstructions of the Eudoxan model, the Moon is assigned three spheres:
- The outermost rotates westward once in 24 hours, explaining rising and setting.
- The second rotates eastward once in a month, explaining the monthly motion of the Moon through the zodiac.
- The third also completes its revolution in a month, but its axis is tilted at a slightly different angle, explaining motion in latitude (deviation from the ecliptic), and the motion of the lunar nodes.
The Sun is also assigned three spheres. The second completes its motion in a year instead of a month. The inclusion of a third sphere implies that Eudoxus mistakenly believed that the Sun had motion in latitude.
The five visible planets (Mercury, Venus, Mars, Jupiter, and Saturn) are assigned four spheres each:
- The outermost explains the daily motion.
- The second explains the planet’s motion through the zodiac.
- The third and fourth together explain retrogradation, when a planet appears to slow down, then briefly reverse its motion through the zodiac. By inclining the axes of the two spheres with respect to each other, and rotating them in opposite directions but with equal periods, Eudoxus could make a point on the inner sphere trace out a figure-eight shape, or hippopede.
Wikipedia
Callippus (c. 370–c. 300 BCE), a student of Eudoxus and of the Academy, extended Eudoxus’ model, adding seven spheres to the original 27, one for the sphere of fixed stars. As we will see, this was the model that Aristotle, with modification, adopted, but which was already rejected by other astronomers in antiquity. However, it enjoyed several revivals over the centuries.
Benjamin Jowett (1817–1893), a Plato expert and translator said, “Of all the writings of Plato, the Timaeus is the most obscure and repulsive to the modern reader.” In the normal run of events the Timaeus should not have had much impact on the unfolding of the history of science. Unfortunately, in late antiquity and the early medieval period the only work of Plato that was widely available to a Latin reading audience was the partial translation of the Timaeus by Cicero (106–43 BCE) and the almost complete translation by Calcidius (late 4. Century CE). George Sarton (1884–1956) one of the founders of the modern history of science in the twentieth century said this about the Timaeus, in his A History of Science (Harvard University Press, 1959)
The influence of Timaeus upon later times was enormous and essentially evil. A large portion of Timaeus had been translated into Latin by Chalcidius, and that translation remained for over eight centuries the only Platonic text known in the Latin West. Yet the fame of Plato had reached them, and thus the Latin Timaeus became a kind of Platonic evangel which many scholars were ready to interpret literally. The scientific perversities of Timaeus were mistaken for scientific truths. I cannot mention any other work whose influence was more mischievous, except the Revelations of John the Divine. The apocalypse, however, was accepted as a religious book, the Timaeus as a scientific one; errors and superstition are never more dangerous than when offered to us under the cloak of science.
[1] James Hannam, The Globe: How the Earth Became Round, Reaktion Books, London, 2023 p. 74
[2] Hannam, The Globe, p. 75