Most pursuits of knowledge in the fifth century were directly continuous with the beginnings laid down in the archaic period, and much of early classical knowledge is classified with late archaic thought under the not always chronologically accurate label ‘‘Pre-Socratic.’’ The natural philosophers of the Milesian tradition became more sophisticated, in the wake of Parmenides’ argument for absolute monism as well as the growing awareness of past achievement enabled by literacy and communication, and most took issue with some aspect of Parmenides’ Truth. Pythagorean wisdom was applied in studies of music, astronomy, mathematics, and also the newly emerging field of medicine. Investigation into the human past and into the causes of great events became more self-conscious of method and more critical of ‘‘mythical’’ approaches. The interest in argument, authority, and proof apparent in Parmenides’ work was reflected in the new arguments about natural philosophy but also continued by the so-called ‘‘Sophists,’’ a group of thinkers with more connections to Greek traditions than many scholarly treatments account for. Although Protagoras, Gorgias, Hippias, and their contemporaries, including Sokrates, may have taken an original impetus from social conditions outside the traditions of formal knowledge, and may have reappropriated the traditional term sophistes to designate a new kind of teacher, both their fields of interest - ethics and justice - and their modes of thought are continuous with those of their Greek predecessors. Developments in knowledge also continued outside of Athens, but from about the mid-450s we see major thinkers drawn to Athens from other Greek cities, whether to visit or to settle.
Cosmology in the fifth century
Perhaps the most influential group of fifth-century natural philosophers were the so-called Neo-Eleatics, those who continued Parmenides’ project sympathetically, especially two famous pupils, Zenon of Elea and Melissos of Samos. Zenon, portrayed by Plato in Parmenides as Parmenides’ close associate twenty-five years his junior, was famous for four paradoxes of motion, apparently intended to refute both the possibility of motion or change in itself and also certain physical theories, such as the infinite divisibility of continua of time and space, that were in dispute along with
Parmenidean monism. More generally, Zenon was credited by Plato and Aristotle with an innovative method in argument, to reveal the deficiencies in an interlocutor’s case by deriving contradictory consequences from it. Melissos, on the other hand, who served as a general for Samos in 441 and so was probably younger than Zenon, seems to have favored physical theory over logic, but, like Zenon, he was chiefly concerned to defend the Eleatic theory from its many challengers. In addition to Zenon and Melissos, it seems that many minor figures (e. g., the brothers Euthyde-mos and Dionysodoros in Plato’s Euthydemos and many figures named or implied in Aristotle’s Topics and Sophistical Refutations) exploited Eleatic arguments without regarding themselves as part of the Eleatic tradition. These men, in some ways the quintessential ‘‘sophists,’’ were not physicists at all but experts in logic and argument or ‘‘eristic,’’ who framed paradoxes by assimilating language to material entities. Since they seem to delight in the paradoxes for their own sake, and seem to lack good faith for the pursuit of the truth, they are given pejorative portrayals by both Plato and Aristotle.
Most strands of fifth-century physics attempted to challenge Parmenides’ argument, as developed by Zenon and Melissos, not always directly, but rather by accounting for its central justified claim against generation and destruction in more plausible ways. Anaxagoras of Klazomenai, the first major thinker known to have settled in Athens (probably about 456/5), where he stayed for about twenty years, and Empedokles of Akragas, who has no known connection to Athens but is said to have traveled widely and to have visited the south Italian city Thourioi, founded in 444/3 as a panhellenic project under Athenian leadership, continued the cosmological speculations of the Milesians in light of the Eleatic argument. Anaxagoras is distinctive for his identification of nous, ‘‘mind,’’ as the cause of the differentiation of the cosmos. Like his predecessors Anaximenes and Parmenides, he thought the world began from a unified original state. Like Anaximandros, he thought this original state was a kind of undifferentiated stuff, which Anaxagoras clearly thought of as a mixture. Anaxagoras departed from his predecessors in the way he explained the separation: Mind, its mechanism, was not an element in the mixture but a discrete entity. Like Parmenides, he ruled out the possibility of any ultimate origin or destruction of what exists. Rather, he innovated previous theories of composition by claiming that all elements of everything are present within everything: it is only the prominence of the black, for example, that makes a thing appear black: the white is also present. Thus he has affinity also with Herakleitos. In fundamental disagreement with Parmenides, and much of tradition, he held that the phenomena accessible to sense perception are roughly similar to real nature. Anaxagoras is said by Plato (Phaedo 97B) to have attracted the interest of the young Sokrates to natural philosophy precisely for his acknowledgement of Mind, presumably because of its anthropomorphic, non-mechanistic, teleological suggestiveness. However, Anaxagoras’ concept of Mind seems not to have been anthropomorphic enough for Sokrates, who demanded that natural philosophy should explain why the composition of the world was for the best, that is, that it should be more fully teleological and non-mechanistic (Hankinson 2003). Anaxagoras is reported to have instructed also Euripides the tragic playwright and Perikles, and the latter allegedly supported him through his trial for impiety c. 437/6, after he shocked the Athenians by claiming that the sun was not a divinity but a stone, and helped him to settle in Lampsakos.
Empedokles, too, accepted the Parmenidean thesis that whatever exists must exist without ultimate origin or destruction, but, like Anaxagoras, he recognized a multiplicity of physical elements, in this case just four - earth, air, fire, and water - and two further elements fundamentally different from these which were responsible for their combination and separation - love and strife, again anthropomorphic, though in an emotional rather than intellectual way. Again like Anaxagoras, he defended the reliability of sense perception, even if his theory required more difference between phenomena and reality than the theory of Anaxagoras. Empedokles was positively influenced by Pythagoreanism and advocated some of its mystical claims, especially the transmigration of souls. His interest in the mechanisms of sense perception, which remained influential for the atomists, may have been connected with the physiological interests of Pythagoreans also reflected in early western (Sicilian and south Italian) medicine. His theory of four elements may have contributed to the further development of medical thought in the newer tradition of eastern doctors, the Hippocratics from Kos who emerged in the mid-fifth century. At the same time, Empedokles is picked out by some Hippocratics as an example of the sort of natural philosopher whose a priori and non-empirical theories are useless and indeed distorting when accepted into the study of medicine.
Anaxagoras and Empedokles had important followers in the second half of the fifth century, who seem to have continued to include humanizing elements in their views of physics, though as far as we know these successors did little to innovate the boundaries of Greek fields of knowledge. Anaxagoras’ pupil Archelaos, apparently Athenian born and, if so, the first known native Athenian philosopher, seems to have followed Anaxagoras in his physics but taken interest also in ethics. Diogenes Laertios claims (2.16) that Archelaos became the teacher of Sokrates after Anaxagoras was forced into exile and that Sokrates’ moral interests were inspired by Archelaos’ discussion of ‘‘laws, the fine and the just.’’ Diogenes of Apollonia (well known by 423, when Aristophanes parodied his views) was probably the most famous late-fifth-century advocate of air as the fundamental principle of everything: it seems to be his views that are reflected in Hippocratic literature (especially Breaths), as well as Aristophanes’ Clouds, and Xenophon’s Memorabilia 1.4 and 4.7. Diogenes, like Anaxagoras, emphasized a principle of intelligence in the composition of things: the Xenophon passages, whatever their source, imply that the intelligence is divine and provident. In both Aristophanes’ Clouds and Xenophon’s Memorabilia we see these views attributed to Sokrates, but Plato’s insistence on a very restricted and short-lived Socratic interest in natural philosophy (Phaedo 96A-99D) has normally been accepted. The theological argument from design in the Memorabilia, if Socratic, need not imply a detailed engagement with natural science.
The clearest and most lasting dissenting response to Parmenidean monism, though, was the atomism of Leukippos (birthplace disputed, dates unknown) and Demokritos of Abdera (c. 460-380 or later), who again accepted Parmenidean requirements of changelessness and indivisibility for what exists, but in place of the one existing thing of Parmenides posited indefinitely many tiny, identical atoma, or ‘‘uncuttables,’’ which existed in an infinite universe of empty space and formed the phenomenal world through various combinations. Though the atoms were identical to each other in material composition, they varied in shape and size, and their position and orientation also determined variety in the phenomenal world. This physical theory was a basis for astronomy and meteorology, but also for atomist theories of the soul, psychology, and epistemology. The ancient catalogue of Demok-ritos’ writings (preserved by Diogenes Laertios 9.46-9) includes lengthy sections on ethics, mathematics, literature and music, and the practical arts, including divination, medicine, agriculture, painting, and military tactics. These titles are supported by very few fragments, however: only in ethics were some of Demokritos’ ideas preserved, and then only in late, aphoristic paraphrases, which resonate suspiciously with Epi-kurean doctrine of the Hellenistic period in privileging a peace of mind achieved through self-control and self-understanding. Since it is likely that the Epikureans, who saw Demokritos as a predecessor, shaped the epitomizers’ choices of texts and the terminology of their paraphrases, we can know little about the connections, if any, Demokritos posited between the atomic theory and these other fields of knowledge. If the connection with ethics is like that we find in Epikureanism, then it is knowledge of the true nature of things that is supposed to free the wise man from false and distracting superstitions. Nor can we attribute to Demokritos certain innovations in developing these other fields: since his lifespan overlaps with the Sophistic and Socratic periods, it is plausible that he was a polymath, engaging in discussion of all the topics of his day. But the conjunction between natural philosophy and ethics apparent not only in Demokritos but in many figures of the fifth century shows the potential shortcomings of our standard view about the history of Greek thought, which assigns natural philosophy to the Pre-Socratics and ethics to the Sophists.
World History
