For those Presocratics who chose not to join the Eleatic camp, the new challenge was to reconcile Parmenides' rigorously argued rejection of change and multiplicity with the obviously changing and varied world of sense experience. Unlike the Eleatics, these philosophers, the pluralists, were not prepared to give up entirely on the world they saw around them, but nor could they ignore Parmenides' formidable logic. Empedocles was the first to face this challenge, and he set the model for all later attempts, by arguing for the existence of certain basic substances of the universe (in his case the four elements) that have many of the key features of the Parmenidean Real. These substances, however, can mix with and separate from each other and thus give rise to the world as we experience it without violating Parmenides' most basic demands.
Empedocles was born in Acragas, Sicily around 492 B.C. He was a philosopher, a medical man, an active politician, and a truly flamboyant figure. He supposedly dressed ostentatiously in flowing purple robes and a gold diadem and even went so far as to call himself an immortal god. As a politician, he supported democracy, although his position as an aristocrat would have made him a likelier proponent of the oligarchy. His exploits in other fields defied expectation to an even more dramatic degree. Legend has it that he managed to keep a woman alive for a month, despite the fact that she had lost her pulse and had stopped breathing. When plague hit the city of Selinus, he managed to divert two streams and thereby rout out the illness. For unknown reasons, he was eventually exiled from his home city. He probably died soon thereafter in the Peloponese, though given his larger-than-life persona it is not surprising that more exciting stories of his death abound. The most intriguing of these, found in Diogenes Laertius, claims that Empedocles' last act was to leap into a crater of Mt. Etna in order to prove once and for all that he was a god.
Despite his hijinks and possible madness, Empedocles was a serious and profound philosopher. Like Parmenides, he wrote in verse, and the poem that survives is dedicated to his lover Pausanius. In this work, Empedocles tells Pausinius about the nature of the cosmos, describing an original pure state from which humans have fallen and to which they may return through a process of purification involving vegetarianism. More important for our purposes, Empedocles' poem also delineates the six basic entities of the world: the four elements, earth, air, fire, and water, and the two motive forces, love and strife. According to his picture, the actions of love and strife result in cosmic cycles in which the elements mix together by love and are pulled apart by strife. These mixings and separations result in the world as we perceive it.
Parmenides and his followers insisted that there was no change in the real world. Empedocles' response was to divide the world into the more real and the less real. On the level of the more real, there are only the four elements (or roots) and the two motive forces. Among these elements and forces there is no generation and destruction—hence, no change. The amount of, say, earth in the world remains constant, and earth never changes qualitatively. Each of the four elements and the two motive forces, then, are Parmenidean Reals.
However, there is also, on this view, the lower level of reality. The world of sensory experience, the world we see and hear around us, belongs to this level of reality. This world comes about as a result of the mixing and separating of the four elements according to the forces of love and strife. Though there is change, generation, and destruction in this world, it is not a violation of the Eleatic demands, Empedocles believed, because these changes were not taking place on the level of the most real things.
Empedocles described in detail how the different mixtures of his elements yielded different substances. In fact, he even explained how different mixtures sometimes yield different degrees of the same substance. For instance, the elemental recipe for blood could be varied to produce different sorts of blood, which in turn corresponded to varying levels of intelligence in the blood's owner. Qualitative diversity, on this view, is grounded in quantitative differences, much like it was on Anaximines' picture.
In the age before Parmenides, Empedocles would not have had to posit the two motive forces. To explain why his elements mixed and separated, he would merely have referred flippantly to eternal motion. In the face of Parmenides' challenge to the very existence of change, however, philosophers could no longer take change and motion for granted. Empedocles, like those who came after him, was forced to both explain what he meant by change and to give a very specific account (by Presocratic standards) of how change occurs.
He, therefore, posited the two motive forces of love and strife. These forces are corporeal, or physical. Their main role is to cause the elements to mix in their proper ratios. Love causes them to mix, strife to separate.
Empedocles speaks about the motive forces as if they really were emotions. He often says that the elements yearn for each other and then come together, or that they get angered and separate. But this is almost certainly just a metaphorical way of speaking; it is very doubtful that he personified his natural world to such a degree. How exactly the motive forces were meant to work, though, if not as motivating emotions, is entirely unclear. Perhaps Empedocles did not think out his theory that far, or perhaps we simply do not have the relevant passages.
As far as the equilibrium of the cosmos is concerned, Empedocles seems torn between the placid state of Anaximander and the fiery state of Heraclitus. The cosmos, as Empedocles envisions them, go through long cycles during which one or the other of the motive forces dominates. When the force of love is in control the universe tends toward harmony, and diversity begins fading; sometimes the universe reaches such a harmonious state that the only diversity remaining is that of the original four elements. When, on the other hand, the individuating force of strife is in control, there is tension between opposites; in this state, objects, qualities, and properties begin to increasingly individuate themselves.
In describing the state and operations of the cosmos, Empedocles floats a theory of the origin of species that hits startling close to Darwinian natural selection. Many species, he explains, arose early on by sheer chance, through the mixing of the elements by love. Only some of these, though, were adapted to survival. Those that were best adapted survived and passed on their characteristics to later generations. Those that were not well-adapted, simply died before propagating. His examples of maladaptive species are particularly fun to thumb through, since they read like descriptions of characters from a goofy, over-stuffed science fiction parody: neckless faces, arms without shoulders, eyes in need of foreheads, men with faces on both sides, ox-men, and androgynous beings.