Aristotle’s distinction of two kinds of action in Metaphysics IX.6, 1048b18-28 makes use of a verbal test: does doing X entail having done X? For instance, ‘I am building a house’ does not entail ‘I have built a house,’ but ‘I am walking’ entails ‘I have walked.’ This makes it appear that Aristotle is distinguishing between performances and activities. But in fact the examples he gives do not seem to work in English. I argue that in fact the verbs which entail their perfect tenses have been mistranslated from the Greek. His examples are of the type: ‘I understand’ entails ‘I have understanding.’ He is distinguishing not between performances and activities, but between performances and states.

It has been claimed that Aristotle always had a theory of matter. But, to the contrary, matter appears nowhere in Aristotle’s “Organon” or so-called logical works, and the concept seems to be incompatible with his early theory of substance, which allows for no substratum below that of substance itself. It seems likely that he developed the concept of matter to allow for the coming-to-be of primary substances, for which he needed a substratum prior to that of substance.

It is often thought that Aristotle’s biological interests account for the unique character of his philosophy. But it is difficult to say exactly how this is. According to a psychological version of the thesis, his attitudes and inclinations bring this about; according to an explanatory version, biological concepts and schemes inform his philosophical concepts; according to a final cause version, his concepts are designed precisely to account for biological theories; according to a historical version, his biological activities preceded his philosophical activities and prepared the way for them. There are problems for all these versions, which emerge in part from his use of craft analogies to explain biological phenomena, where it appears that human activities precede and are prior to biological researches. But Aristotle does seem to be motivated by a pre-theoretical interest in living things, which he often used non-biological theories to explain.

Aristotle is traditionally thought to have a doctrine of prime matter, positing the existence of a primitive kind of matter of the four elements. This doctrine has become increasingly controversial. Supporters are right to see systematic reasons in Aristotle’ theory for the doctrine, but detractors are right to worry about it, for prime matter proves to be an incoherent concept, as being the foundation of all change but having no identity conditions it can fulfill.

The question, 'What is history of philosophy?' has scarcely been answered. We may find a model for it in Saussure's linguistics: there is a synchronic or systematic study, and a diachronic or genetic study. Philosophical structures can similarly be seen as a sequence of states or positions at different times. Philosophical changes are made to increase the perceived explanatory power of the system. In this goal, history of philosophy differs from doxography and history of ideas. In the history of philosophy systematic analysis is subordinated to genetic analysis.

We think of anachronism as a vice to be avoided by historians of philosophy. But our relationship with the past is a complex one. Aristotle provides a history of the development of causal concepts by his predecessors. He seems to treat them as ignorantly moving toward his theory of the four causes. In order to learn from the past, we must explore their conceptions by means of using our own conceptions. We must apply modern conceptions to them even if we do not attribute those concepts to them. Aristotle can be see as reconstructing a history in light of his more advanced concepts. This does not entail that he misconstrues his predecessors, but only that he interprets their past thought in light of its implications for the present.

The schemes of potentiality-actuality and matter-form are usually treated as alternative schemes that do the same work. But, to the contrary, they are complementary schemes that are individually inadequate but jointly sufficient. The matter-form scheme explains how an individual substance can come-to-be without coming-to-be from nothing, answering Parmenides’ objection: there is a pre-existing matter from which it arises, when the form supervenes on the matter. But form, according to Aristotle, is unitary and indivisible. How then does it happen that change (e.g. the birth and growth of Socrates) can be gradual? Aristotle introduces a sliding scale of change, actuality, which allows for a gradual development from a potential to a complete state, e.g., from acorn to full-grown oak. While the matter-form scheme answers Parmenides, the potentiality-actuality scheme answers Zeno.

Scholars debate whether in Empedocles’ cosmic cycle there is a single creation of living things or two moments of creation. An examination of Empedocles’ poetic tropes reveals that he always presents the stage when Love advances before the stage when Strife advances, in a mimetic pattern. The two-fold development includes a two-fold creation, once under increasing Love, once under increasing Strife.

Aristotle defines motion as ‘the actuality of what is potentially, as such.’ According to current analyses, (1) ‘actuality’ signifies a product, not a process; (2) ‘as’ is ambiguous; (3) the definition must be explicated in terms of Aristotle’s different levels of actuality. But Aristotle resorts only to examples to explicate his own definition, such as, ‘when the buildable is actual, it is being built.’ The actuality in question is the activity, not the product of the action. The ‘as’ focuses attention on the subject expression itself: the build-ABLE. And the definition can be explicated by a linguistic transformation without a metaphysical excursus: the buildable is activated by being built.

The term entelecheia derives not from (to) enteles echein ‘have completeness’ (H. Diels) or en heautōi telos echein ‘have an end in itself’ (K. von Fritz), but entelōs echein ‘be complete.’ Aristotle seems to develop the term to avoid the ambiguity of energeia, which originally implied ‘activity’ but came to denote the final result of that activity.

In a discussion of my book, Aristotle’s Two Systems (Oxford, 1987), I defend my position against objections by Christian Wildberg and Owen Goldin.

Soon after Plato’s death a controversy arose over whether Plato’s story of the creation of the cosmos was literal or allegorical. Plato seems to give a creationist account, in which the Demiurge or cosmic designer uses eternal paradigms to structure the world. According to Plato’s argument: (1) what is grasped by reason always is; (2) what is grasped by opinion comes-to-be; (3) whatever comes-to-be comes-to-be from some cause; (4) what comes-to-be is visible and has body; (5) whatever is visible is grasped by opinion through sensation and comes-to-be; (6) the cosmos comes-to-be; hence (7) the cosmos has a cause. But in Plato’s theory of knowledge what comes-to-be does not ever arrive at completion, so the argument is problematic.

Socrates uses analogies with the crafts such as building and medicine to point out how moral educators fall short of the professional standards of craftsman of his day. But he uses the crafts as a kind of model for positive purposes too. Socrates recognizes at least three important features of crafts: (1) they are organized to reach a goal external to the crafts: a product such as a house or a state such as health; (2) they employ established methods for reaching the goal that are effective; (3) they require a level of expertise beyond what the untrained individual has. He further holds that (4) the crafts are unerring in their endeavors. And (5) their goal is some significant social good that makes them worthwhile. Thus the crafts are institutionally altruistic and offer an ideal for practical knowledge in general and for moral reasoning in particular.

What is the relationship between Socrates and his follower Plato? Did Plato “invent” Socrates or did Socrates inspire Plato? A comparison with the career of Ludwig Wittgenstein shows that a charismatic and revolutionary thinker can inspire a generation of students, who do not always agree with each other about their master’s doctrine. Plato had to recreate Socrates to promulgate his views, and he had the mental acuity and literary talent to do that, more than any of the other Socratics. He never agreed with Socrates on some fundamental issues, such as the ability of common people to be benefited by philosophy, yet he presents Socrates as firmly holding that view in Plato’s early or Socratic dialogues. Only in the middle-period dialogues does Plato make Socrates a mouthpiece for Platonic theories. Plato did not invent Socrates, but rather without Socrates there could have been no Plato.

G. Kerferd identified five principles or postulates of Anaxagoras: (1) No Becoming; (2) Universal Mixture; (3) Predominance; (4) Infinite Divisibility; and (5) Homoeomereity. All postulates are advocated in the fragments of Anaxagoras except the last. We can find a deductive justification for Universal Mixture, the claim that every kind of matter is mixed with every other kind. It may seem that only if matter is homoeomerous (has parts that are the same in kind as the whole, for instance, water is made up of portions of water), can Universal Mixture be true. But Chaos Theory will allow for fractal patterns that repeat all the way down without being homoeomerous. He seems to wish to explain the world in a non-reductive way.

A theory of the how Aristotle’s concept of actuality developed is critiqued.

There is a difference between Aristotle’s account of natural motion in Physics II and in Physics VIII: in the former simple bodies, the four elements move up or down by themselves because that is their nature; in the latter they have a passive power activated by the unmoved mover. Aristotle seems to have made a development in his theory stressing the importance of final causes, without fully resolving how there can be natural motions on the new theory.

In the ancient world Heraclitus is known for five doctrines: (1) fire is the source of all things; (2) there are periodic episodes of world conflagration; (3) everything is in flux, in constant motion; (4) the opposites are identical; and (5) in consequence of (3) and (4), Heraclitus violates the Law of Non-Contradiction. Modern critics have refuted (1) and (2) and challenged the other doctrines, making Heraclitus a constancy theorist; but other scholars have defended him as a flux theorist holding (3), (4), and (5). I argue that it is possible to combine elements of both views—Heraclitus believes in both constancy and flux—in an interpretation that avoids the logical chaos of point (5). In criticizing his predecessors, Heraclitus opposes not Material Monism but the Generating Substance Theory, which already implies that elemental stuff change into each other. But he recognizes that if that is so, there is no privileged generating substance, only a lawlike sequence of changes. There is a unity of opposites, but not an identity; and flux at the level of elements is balanced by constancy of natural structures, including that of the cosmos itself. So there is both low-level flux and high-level constancy, and Heraclitus’ paradoxes are resolved without contradiction.

Three points in Socrates’ theory and practice seem to be incompatible: (1) the disavowal of knowledge: Socrates has not special knowledge; (2) he holds that virtue is knowledge; (3) Socrates is, in his behavior in public and in private, supremely virtuous. How can we reconcile these points? In the Crito and the Apology we see Socrates acting on what he thinks is right rather than for his own personal advantage. He says that he has one advantage over others: he does not pretend to know what he does not in fact know. And he does not know whether death is the greatest of evils or a great good. So he does not take into account his own personal welfare in making his moral deliberations. Accordingly, his knowledge of what he knows and does not know makes it possible for him to act virtuously.

Empedocles posits four elements which combine to produce temporary compounds. There is cosmic cycle in which living things are produced and then destroyed, and a unified Sphere alternates with a cosmos. Anaxagoras sees the world as arising from a vortex motion which separates substances from a complete mixture. He posits a large number of elemental stuffs that mix with each other. Both philosophers are reacting to Parmenides’ rejection of change, but they do not seem to arrive at his conclusion that there is no natural world. Commentators describe them as desperately and vainly trying to save natural philosophy from Parmenides. Yet Empedocles and Anaxagoras do not even try to refute Parmenides’ view; instead they agree with his claims that there is no coming-to-be or perishing. Parmenides concludes that what-is must be (1) everlasting, (2) all alike, (3) unchanging in its nature, and (4) complete. He seems to reject dualism with its contrary properties, but not necessarily pluralism. Empedocles and Anaxagoras can both maintain that their theories conform to Parmenides’ four Eleatic requirements. Zeno and Melissus later challenged the new pluralist theories as still inadequate. But there is a sense in which the pluralists saw themselves as followers of Parmenides rather than as his opponents.

The Christian church arose in the early Roman Empire at a time when Greek culture dominated the empire and Greek philosophy marked the highest level of intellectual attainment. Christian leaders adopted different attitudes to the prevailing culture. Christians could shun secular culture altogether, as Tertullian advocated; embrace what was good and acceptable, as Clement of Alexandria recommended; or use Greek sciences as a model for religious knowledge, as Origen did. Eventually philosophical theories, especially Platonism, came to inform Christian beliefs, sometimes to the detriment of revealed truth.

Who discovered that reflection from the sun was the source of the moon’s light? The discovery is often attributed to Thales, but if he made the connection, why did his successors remain unaware of it? Other early natural philosophers, including Pythagoras, seem to be unaware of the real source of the moon’s light. We first find the correct theory in the cosmology of Parmenides, in frs. 14 and 15, where he offers empirical evidence for the view. This discovery entails several other truths about the heavenly bodies, and suggests a way of understanding eclipses, which his successors would exploit. This discovery indicates that Parmenides was not just a critic of cosmologies, but a formidable cosmologist in his own right.

What is the relationship, if any, between Heraclitus and Parmenides? It is implausible to think that Heraclitus was reacting to Parmenides, for he names and criticizes his opponents. But Parmenides could be reacting to Heraclitus—or not. There are eight sets of parallel passages in the two philosophers, but it is an open question whether they reveal influence of Heraclitus on Parmenides. In these passages we find Parmenides not only echoing Heraclitus’ language but imitating his unique wordplays including chiasmus and syntactic ambiguity. Parmenides’ dialectical opponent holds that to be and not to be are the same and not the same, and that the path of all is backward-turning; Heraclitus fits the bill. The evidence suggests that Heraclitus was to Parmenides as Hume was to Kant: the motivation for a radical revision of philosophy.

Traditionally Anaximenes is understood to be a material monist for whom the ultimate stuff of the cosmos is air, and to have a unique theory of change according to which air turns into other stuffs by rarefaction or condensation. G. Wöhrle has criticized the latter view on the basis of one testimony. Although no one before Aristotle mentions Anaximenes by name, we find reactions to his work in Plato, Parmenides, Anaxagoras, and Melissus, which confirm his theory of change. These testimonies, however, call into question the claim that Anaximenes was a material monist. It is likely that there was only one material monist among the Presocratics: Diogenes of Apollonia, whose view that air was the source and substance of all things was confused with the theory of Anaximenes.

The Greek construction ‘philein + infinitive’ does not mean ‘loves to’ but ‘is wont to,’ as can be seen in its usages in contemporary literature, and ‘phusis’ is not usually taken to mean Mother Nature in archaic thought, but to denote an individual nature. Thus Democritus fr. 228: if children fail to follow parental guidance, phileousi diaphtheiresthai they inevitably are ruined; they surely do not love to be ruined. So Heraclitus is not saying ‘Nature loves to hide,’ but ‘a nature is hidden.’

No author before Aristotle mentions Anaximenes by name, but there is an important allusion to him in Plato that offers a valuable perspective. In Timaeus 49b-e, Plato gives a theory of elemental change that echoes that of Anaximenes in the seven elements, the order of change, and the mechanisms of change. According to Aristotle and the Peripatetic tradition, Anaximenes is a material monist who posits one single elemental stuff that changes its appearance but not its nature. Plato sees Anaximenes as a pluralist whose elements are radically transformed into one another. This view may be said to be Heraclitean, but it is possible that it is a view of change that Anaximenes shares with his near contemporary Heraclitus. Indeed, Anaximenes’ theory of change may provide Heraclitus with the impetus for his critique of Ionian philosophy.

Although in the Apology Socrates claims that he goes around exhorting people to moral excellence, in the dialogues we never see him exhorting anyone, but only examining definitions of virtue. We can understand Socrates’ claim by appreciating his intellectualism: he believes that human beings naturally seek the good; only by knowing what is good can they achieve it. On this view, the soul can be likened to a set of propositions. The soul can achieve the good only if all the propositions are consistent. According to this model many of Socrates’ paradoxical views make sense. Moral agents do not need exhortation but logical examination; virtue is not teachable, but it is achievable through constant examination.

Anaximenes is generally held to recognize a sequence of seven basic elements from the most rare to the most dense. This view has been rejected on the basis of testimony A6 from pseudo-Plutarch, most recently by G. Wöhrle, who claims that the view has been invented by later commentators. But we find echoes of the view in Anaxagoras, Melissus, and Plato, showing that Anaximenes did hold the view.

In his tour of Egypt Herodotus attempted to determine the source of the Nile River and explain the curious fact that it flooded in summer rather than in winter, the rainy season when Greek rivers flooded. He reveals the impact of Greek philosophical theories by testing and refuting theories of the Nile floods, while using the same methods and naturalistic assumptions as the philosophers. Ongoing philosophical debates may have helped preserve early theories such as that of Thales.

Anaxagoras seems to posit a universal mixture of an indefinitely large number of homogeneous stuffs or elements, recognizing not just the four elements of Empedocles (earth, water, air, fire), but e.g. flesh, bone, iron, gold, etc. P. Tannery followed by J. Burnet proposed that Anaxagoras’ apparently lavish ontology could be reduced to combinations of basic powers or qualities such as hot, cold, wet, dry. This interpretation has been very influential. But G. Kerferd as shown that Anaxagoras’ theory can be made consistent without reducing stuffs to qualities. According to Anaxagoras, whatever stuff is present in a mixture in the largest quantity will be made manifest, i.e., give its character to the whole. This allows elements to be known not by definition but by acquaintance. This theory implies that every stuff is already present in the mixture, not merely potentially present as the Tannery-Burnet theory would have it. If Anaxagoras’ theory is lavish, it is also responsible to Eleatic concerns. It posits a large plurality of beings, but rejects different levels and complex interrelations of beings.

Plato’s writings defended Socrates’ mission and were largely responsible for making philosophy into a study to be admired and sought after. But his most gifted student, Aristotle, in many ways eclipsed his master. When Plato distinguishes between a property and the bearer of the property in the Phaedo, he does so thirty Stephanus pages after introducing the topic. By contrast, Aristotle uses the insight to build a general theory of change involving a substratum, properties, and time, in Physics I and exploits it in a systematic way in all his writings. At the end of Republic I Plato discusses the good life as realizing human functions, but lets the discussion drop. In Nicomachean Ethics I 7, Aristotle builds the foundation of his whole ethical system on Plato’s distinction. In the Sophist Plato recognizes that a combination of a noun and a verb can make a statement that is true or false and that we can describe objects in different ways. In his Categories Aristotle points out that only a statement (not, for instance a command or a wish) can be true or false, and that truth and falsity are properties of statements; he also classifies the different ways words can connect with things and develops systematic categories of being. Plato is clearly the inspiration for Aristotle, but Aristotle systematizes many of the insights of Plato into rigorous theoretical positions.

Thales is reputed to have helped the Lydian army cross the Halys River in their war with the Persian Empire, by a clever piece of hydraulic engineering. But he is also famous for having counseled his city not to join other Greek cities in a military alliance with Lydia. Had he rendered valuable aid to the Lydians, he would have made Miletus an enemy to Persia. In fact, when Persia defeated Lydia and subjected Greek Ionia to Persian rule, Miletus was the only Greek city that Cyrus made a treaty with, preserving its independence.

Christian leaders originally saw Greek philosophy as providing common ground between Christians and non-Christians in a shared concern for ethics and truth. Philosophical principles came to be used a way of organizing knowledge, but eventually philosophical methods were taken into theology as a way of solving doctrinal problems with logic and reason rather than revelation.

What are the forces that govern Empedocles’ cosmic cycle, and how do they act? According to the Displacement Theory of M. R. Wright, Strife advances toward the center of the cosmos, until Love darts from the circumference to the center and drives it back. According to the Distribution Theory of A. A. Long, Strife shatters the homogeneous Sphere into elemental fragments, which Love, acting from the center, slowly brings together. In the Oscillation Theory of D. O’Brien, Strife is based at the circumference and advances toward the center, until Love begins to push out from her base at the center of the cosmos, causing Strife to retreat. Our evidence suggests that the Sphere disintegrates from the outside in, consistent with the Oscillation Theory. That theory makes the best military sense as the invasion of a city-state from the borders to the polis, with a counterattack from the polis. The role of Love is consistent with the action of harmony in city politics, in which political unity can be achieved only by reconciling unlikes, the Haves and Have-nots, who otherwise separate into hostile factions.

Ancient sources credit Anaxagoras with the correct account of solar and lunar eclipses. But did he get that account from his predecessors or from his contemporary Empedocles? There is no evidence that earlier thinkers had the correct understanding of eclipses. A study of fifth-century BC eclipses will help determine who first proposed the theory. According to M. L. West, the solar eclipse of 557 BC provided the data; according to D. Sider, that of 463 BC. The first event is dubious because it occurred some eighty years before Anaxagoras, in a time when there were no scientific archives, and the eyewitnesses were either deceased or were too young to recall the eclipse. The second passed over Thessaly in central Greece, whereas Anaxagoras used the Peloponnesus to gauge the size of the moon and son. But the umbra of the annular eclipse of 478 BC did pass over the Peloponnesus. According to one account, the young Anaxagoras was in Athens at the time, and able to collect observations from sailors and passengers from the area. The slightly younger Empedocles held the same theory of eclipses but lived on the island of Sicily where the umbra of the eclipse did not fall. On the theory that the moon was illuminated by the sun, proposed recently by Parmenides, and the (false but plausible) assumption that shadow of the moon was the same size as the moon itself, Anaxagoras inferred that the moon was about the size of the Peloponnesus, using empirical evidence for his deduction. He not only proposed but “proved” his theory of eclipses.

Diogenes Laertius tells us (2.23) that, according to Ion of Chios, the young Socrates made a trip to the island of Samos with Archelaus. This has been construed to mean that Socrates was part of Athens’ military campaign against Samos in 440 BC. But Socrates was not particularly young then, nor does the reference say anything about a military expedition, but implies Socrates was accompanying his philosophical mentor. Ion was himself a philosopher and an Ionian interested in Athenians visiting his native territory; since he died around 422, he wrote this notice when Socrates was alive and becoming prominent. Evidently Socrates embarked on a philosophical trip a decade earlier than the military campaign. The obvious objective would be the famous philosopher of Samos, Melissus the Eleatic. This suggests a showdown between the cosmologist Archelaus and the anti-cosmologist Melissus that may have colored Socrates’ views about the feasibility of speculations on natural philosophy.

Heraclitus writes in the wake of cosmologists such as the philosophers of Miletus; but he emphasizes not science but the human condition. He is reputed to be a philosopher of flux, but how is knowledge even possible if the world is in constant motion? Heraclitus does believe that fire turns into water, which turns into earth, and vice versa. There is constant physical change, and radical change at that, since the death of one element is the birth of another. Yet there is constancy too: the ratios of the elements remain the same as one change is balanced by its contrary. Paradoxically, the transformation of the elements supports a permanent cosmos in which the major bodies remain unchanged. Heraclitus’ fr. 12 is often interpreted to mean that you cannot step twice into the same river. But what it says is that the same rivers are composed of ever different waters; in other words, if the waters were not constantly changing you would have, not a river, but a dry streambed, or perhaps a lake. As with the cosmos, a high-level order supervenes on material flux. But fr. 12 is also syntactically ambiguous, as in this rendering: “On those stepping into rivers staying the same, other and other waters flow.” The phrase ‘the same’ can be construed with ‘those stepping in’ as well as with ‘rivers’: different waters flow on those fording the river—who thereby stay the same. According to Heraclitus, philosophical knowledge consists not merely of sense experience, but of grasping the deeper connections: we become independent agents by resisting opposing forces, and the world becomes a unity by constantly being transformed. The world is a riddle to be solved, and the philosopher educates us by posing riddles.

Leucippus is the reputed founder of atomism, but we know almost nothing about him. Was there such a philosopher? What, if anything, did he write? What, if anything, did he contribute to philosophy? Theophrastus claimed he invented atomism and wrote the Megas Diakosmos, The Great Cosmology. That work contains a cosmological theory inconsistent with the theory of Democritus. According to the Great Cosmology, which Theophrastus attributes to Leucippus, the moon is the heavenly body nearest earth, the sun is the most distant, and the stars and planets lie between them the sun and moon. But according to Democritus the sun lies between the moon and the planets and stars. The author of the Great Cosmology the drum-shaped earth tilts toward the south because the southern air is warmer and rarer; according to Democritus the disk-shaped earth tilts to the south because it has a greater biomass. Thus we have two competing cosmologies, presumably by two different authors. In the Lesser Cosmology, Democritus says he was young when (his master) Leucippus was old. There are indications that Leucippus developed atomism as an extension of Parmenides’ cosmology, with its two elements, fire and night, being rare and dense, respectively; Leucippus makes one “element” completely rare, the void, and one completely dense, the matter of the atoms. Melissus seems to criticize an already-familiar theory of atoms, presumably that of Leucippus. Democritus seems to react to Melissus and to attack Parmenides’ ontology rather than elaborating on Parmenides’ cosmology.

Heraclitus recognizes flux as a fundamental fact of the world, but this fact threatens to make knowledge inaccessible. How is knowledge possible for him? A study of his paradoxical statement shows that in his verbal complexity he imitates the structural complexity of the world. By solving his riddles we discover the patterns of the world. For instance, in the river fragment (fr. 12) and other statements we find that the more things change the more they stay the same. Unlike most philosophers, Heraclitus stresses induction from examples over deduction from principles, but he sees the road up and the road down as one and the same.

Around 466 BC a fiery meteoroid fell to earth in Aegospotami in northern Greece, leaving a large meteorite. The event was said to have been predicted by the philosopher Anaxagoras. Ancient sources report that a comet was seen shining in the sky at the same time, a comet that was visible for seventy-five days. Modern reconstruction estimate that Halley’s Comet would have been visible during this time, and Chinese records confirm that sighting of a comet. Anaxagoras posited the existence of asteroids which under certain conditions could fall out of orbit and crash to earth. It is likely he anticipated the possibility of a meteor strike, which was taken to have been confirmed by the stone of Aegospotami.

Scholars recognize that the Presocratic philosophers were deeply concerned with giving a scientific account of the world. However, they further object that (A) they were ingenious, but naïve, theorists; (B) they were imprecise in their observations and incompetent in their handling of empirical evidence; hence, (C) they did not achieve a scientific understanding of the world. I provide three studies to challenge these points: Parmenides discovered the source of the moon’s light; Anaxagoras discovered the correct explanation of solar and lunar eclipses; Anaxagoras predicted the possibility of meteoroids falling to earth, which was confirmed by a meteor strike during his lifetime. Some theories of the Presocratics were vindicated by natural events and became paradigms for later scientific researches.

Heraclitus is often held to hold the principles of Flux and Material Monism. By the first all things are changing in some respect; by the second all things are one substance, namely fire. It is seldom noticed that these two principles are in conflict: if Monism is true, there is at least no radical change, but only changes of accidents or incidental features; if there is radical flux, then all things are not one. In fact Heraclitus expressly commits himself to the view that the elemental stuffs of the world change radically into one another: the death of one is the birth of another. Yet he also hold that there is global stability: the cosmos itself is stable. In the river fragment (fr. 12), the same rivers are composed of ever different waters. There is a deep insight in Heraclitus’ theory. In modern science, we see that the human body is constantly losing and creating cells and turning nutrients into energy. The universe itself is constantly changing but supporting stable stars and planets. Heraclitus is a process philosopher who presciently sees order arising underlying and emerging from flux.

Anaxagoras developed a theory of matter designed to follow the principles laid down by Parmenides in his critique of earlier philosophies of nature. He also drew on Parmenides’ insight that the moon gets its light from the sun. Using the insight, Anaxagoras hypothesized that eclipses are caused by the blocking of the sun’s light by the moon (solar eclipse) or the earth (lunar eclipse). He used that hypothesis to determine that the moon must be approximately the size of the Peloponnesus, based on the umbra of a solar eclipse in 478 BC. Anaxagoras said that there were asteroids in the heavens which might fall to earth. When a meteor crashed in northern Greece, it confirmed his theory and added to his credibility as a scientist. Eclipses have served as important markers of scientific progress, including the eclipse of 1919 that confirmed Einstein’s general theory of relativity.

Around 466 BC a fiery meteoroid fell to earth in Aegospotami in northern Greece, leaving a large meteorite. The event was said to have been predicted by the philosopher Anaxagoras. Ancient sources report that a comet was seen shining in the sky at the same time, a comet that was visible for seventy-five days. Modern reconstruction estimate that Halley’s Comet would have been visible during this time, and Chinese records confirm that sighting of a comet. Anaxagoras posited the existence of asteroids which under certain conditions could fall out of orbit and crash to earth. It is likely he anticipated the possibility of a meteor strike, which was taken to have been confirmed by the stone of Aegospotami.

The alleged Heraclitean doctrine that you cannot step twice into the same river was challenged long ago by K. Reinhardt, followed by G. S. Kirk and M. Marcovich. Recently L. Tarán has defended the traditional doctrine. But a comparison of the alleged river fragments of Heraclitus shows they all have the same vocabulary and (unusual) word order of fr. 12, and are likely paraphrases of it. But that fragment contrasts the sameness of rivers with the changing characters of the water flowing in them. Heraclitus’s point is that the ever-changing waters sustain the constancy of the rivers, or, more generally, the more the materials of the cosmos change, the more the cosmos stays the same.

It is generally held that the cosmologies of the Presocratic philosophers were unique and based only on private speculations. But a survey of cosmologies shows an important shift from the sixth century to the fifth century BC. The earlier cosmologies feature heavenly bodies that are as light as or lighter than air, that sometimes are “new every day,” and that travel above the plane of the flat earth. The later cosmologies feature heavenly bodies that are heavier than air, are permanent structures, and that travel below as well as above the earth. This change seems to result from the insight of Parmenides that the moon gets its light from the sun, which entails, among other things, that the sun is shining on the moon in the middle of the lunar month when the sun is below the earth and the moon above it. The moon, being an opaque, spherical, earthy body, must be held aloft by a powerful vortex motion, not an earth-generated wind. This conception led to a correct solution to the problem of how eclipses occur, which then rendered all earlier models of the cosmos obsolete.

There is a debate as to whether the Presocratics are the inventors of natural theology or positivists who seek to subvert traditional religion. An examination of the Presocratics show that they allow for divine attributes in the world, but they associate these with natural principles, for they seek to make nature an autonomous realm. Only Xenophanes glimpses the notion of a transcendent deity who governs the world. Other Presocratics develop a theology of nature rather than a natural theology of a supernatural being.

An examination of the theories of the early Ionian philosophers shows that they share a naturalistic approach to the world. They propose look for lawlike regularities in the world and they come to reflect critically on attempts to explain it, offering increasingly sophisticated methods for understanding phenomena.

Critical studies of early Pythagoreanism have shown that Pythagoras’ status as a philosopher is dubious, while the Pythagorean Philolaus has emerged as an important figure in Presocratic philosophy. He posits as elements limiters and unlimiteds, which combine to constitute the objects of experience. He develops an innovative “hestiocentric” cosmology in which a cosmic “hearth” (hestia) is the center of the cosmos and the Earth a planet circling it once every day. He posits a counter-earth, and Earthlike planet inside the Earth’s orbit that is responsible for some lunar eclipses. He applies his theory to biology and psychology, and in general seems to respond to developments of Ionian natural philosophy. He seems to have been one of the first philosophers to stress the role of order, structure, and number in nature.

The Greek term grammatikē in Plato and Aristotle is typically translated ‘grammar’ and the adjective grammatikos as ‘grammatical’ or (in a substantive use) ‘grammarian.’ These terms in classical usage never refer to grammar. A close examination of passages in Plato, Aristotle, and Xenophon shows that grammatikē means ‘literacy,’ knowing one’s ABCs. Literacy serves as a paradigm of knowledge because it is precise and (when one is fully literate) infallible.

Aristotle and others criticize Philolaus’ cosmos for being too a priori and unempirical. He invents a central fire or hearth around which the Earth and other planets move, and he invents a counter-earth so that there might be ten heavenly bodies (a perfect number). But there is a reason for him to posit an additional earthlike planet. Following Anaxagoras, Philolaus holds that eclipses are caused by the blocking of the sun’s light. When a lunar eclipse happens at dawn or dusk, the Earth is out of position to block the sun’s light to the moon on Philolaus’ model. But if there is another planet inside the Earth’s orbit, it can block the moon’s light.

The concept of material entities is found in the Presocratics, without a general term, which is invented by Aristotle. The basic stuffs of the world are first conceived as changing into one another, then, after Parmenides, as having a fixed character as elements. Plato explores the notion of matter in the Timaeus. Aristotle posits matter as the substratum of substances, allowing them to-come-to be and perish. The Epicureans and Stoics elaborate on earlier theories of matter, while later Platonists follow Plato’s suggestions. Early Christian theorists for the first time accept the notion of creation of matter ex nihilo.

In the Timaeus, Plato sympathetically describes Anaximenes’ theory of matter, with its seven states of matter, its contrary mechanisms of rarefaction and condensation, and notion that the birth of one element is the death of another. Plato treats Anaximenes as a kind of philosopher of process rather than a material monist, as Aristotle portrays him. From this perspective, Anaximenes can be seen as a forerunner of Heraclitus rather than of Diogenes of Apollonia. Plato seems to introduce Anaximenes’ theory as an approximation of his own theory of matter. Plato’s interpretation may be inspired by the readings of Cratylus and other Heracliteans and have its roots in a pre-Parmenidean worldview. Although it conflicts with Aristotle’s better-known and more Eleatic interpretation, Plato’s interpretation is at least as old, and deserves serious consideration as the only other early understanding of Anaximenes.

In his Apology of Socrates, Plato has Socrates defend himself in his trial for impiety by saying that he has a mission from God that he has been pursuing. He says that he teaches people to care more about the welfare of their souls than about, money, power, or reputation. Yet in other dialogues Socrates never preaches, but seeks definitions of virtues. Socrates says in the Apology that he has no special knowledge, but he has one advantage: he does pretend to know what he does not know. He expands on this by saying that he does not know that death is the greatest of evils, and so he does not take death into consideration when he is judging what is right and wrong. This small advantage allows him always to choose the right over the expedient. In fact, he sees his pursuit of virtue as showing people how to eliminate beliefs that get in the way of making moral choices. He was condemned and executed by Athens, significantly dying on the Athenian Day of Atonement. He was appropriately seen by early Christian thinkers as a proto-Christian martyr.

In Plato’s Apology of Socrates, Socrates attributes his sense of mission to Chaerephon’s embassy to the Oracle of Delphi; the oracle said that no one was wiser than Socrates, and Socrates felt duty-bound to test the remarkable assertion. This account appears only in the trial speeches authored by Plato and by Xenophon, and its reliability is controversial. If it Chaerephon did consult the oracle, when did he do it? Most scholars who accept the story date it either around 431 BC or around 421 BC, because between those dates the Peloponnesian War was raging and Delphi was in enemy territory. But the dates are too early or too late to account for Socrates’ rise to notoriety, which culminated in two plays being performed about him in 423. In fact it was possible to travel to Delphi during the “sacred truce” that prevailed leading up to the Pythian Games held at Delphi in 426, which allowed pilgrims safe conduct to and from the religious festival. This would allow time for Socrates to test the oracle by examining alleged wise men. By the time of Socrates’ trial, Chaerephon was dead, but his brother, presumably Chaerecrates, a member of Socrates’ circle, was probably called on to give independent testimony of the event. Thus the Chaerephon story is historically plausible.

Greek ethics is almost universally held to be goal-directed (“teleological”) and aimed at happiness (“eudaimonistic”), including the ethical views of Socrates, the founder of the tradition. But the Socratic dialogues of Plato provide evidence that Socrates’ ethics was duty-based (“deontological”). The Crito shows Socrates making a moral deliberation about whether to break out of prison with the help of his friend Crito, who has bribed the guards. In his arguments he focuses on what is the morally right thing to do, to the exclusion of what is to his personal advantage. To break out of prison would be to do wrong and to do harm to the laws of Athens. He rules out wrongdoing not on the basis of actual harm done or pain inflicted, but on the logical grounds that to do wrong is to make someone worse, i.e., more unjust, which cannot be the work of justice. In the Apology he claims that he urges people to care more for their souls than their bodies, and to do what is right rather than what is advantageous. Whereas some scholar see Socrates as saying that we always aim at our own good, he seems rather to say that we always aim at the good in general; accordingly, virtue is knowledge (of what is really good and evil). Socrates should be understood to be a deontologist, or perhaps (in view of the lack of developed distinctions in his time) a proto-deontologist.

The Presocratics developed cosmological theories based on natural regularities rather than divine interventions into nature. Their theories became more sophisticated and also began to make scientific progress in accounting correctly for the light of the moon, for eclipses, and meteors. Theories of matter came to stress combinations of permanent elements, which became the forerunners of modern chemical theories. Plato developed a theory of nature consistent with the cosmos being designed for the best by a cosmic craftsman or engineer. He posited a spherical earth at the center of the cosmos and viewed the heavenly bodies as traveling in orbits driven by complex forces.

In Phaedo 96 ff., Plato criticizes early Greek natural philosophy for its failure to explain why Socrates is in prison. This seems like an absurd demand, until we remember that the Ionian scientific program seeks to create a unified science that will explain every event in the world, relying on a naturalistic explanation for every event. But no series of natural explanations, for instance of how Socrates’ bones and muscles are arranged, will account for why he is in prison, since he is there because he willed to stay rather than to escape, as seen in the Crito. Hence there is a counterexample to the program of natural philosophy. Plato could, then, like the historical Socrates, dismiss natural science altogether. Instead, he has his character Socrates suggests a goal-directed or teleological theory could explain his being in prison, and potentially every other event in the world. Thus teleological explanation could in principle replace or supersede naturalistic explanation. Although Plato backs off from offering purposive or teleological explanations in the Phaedo, he does offer a system of teleological explanations in the later Timaeus, with the Demiurge or cosmic engineer arranging things in the cosmos for the best.

We can follow the rise of empirical astronomy from its beginnings in the early fifth century BC. Parmenides discovered “heliophotism,” the recognition that the moon gets its light from the sun. Anaxagoras used this insight to discover the “antiphraxis” theory of eclipses, according to which eclipses are caused by the blocking (antiphraxis) of the sun’s light. These views were taken over by Empedocles, a near contemporary of Anaxagoras, and quickly adopted by other natural philosophers. Thucydides was aware of the theory and used it to criticize Nicias’ superstitious response to a lunar eclipse during the Athenian siege of Syracuse. Aristotle cited antiphraxis as a paradigm of scientific explanation. It was accepted by the Stoics. And the mathematical astronomers from Aristarchus on used it as a principle of astronomy. In the doxographic tradition the discovery of heliophotism and antiphraxis was attributed to Thales or Pythagoras, but there is no evidence to support that attribution. Plutarch studied the question and recognized Parmenides, Anaxagoras, and Empedocles as the earliest proponents of the theories.

Parmenides’ Aletheia receives the lion’s share of philosophical scrutiny. His Doxa, focusing on the explanation of natural phenomena, by contrast, is often neglected, especially in studies focusing on metaphysics. But it is the latter that occupied most of Parmenides’ poem and which had, arguably, a more profound influence on later philosophy. The Doxa seems to embody the Eleatic properties Parmenides attributes to the proper object of understanding, at least as far as possible in a theory designed to account for change. Apparently for the first time, it attempts to explain changeable phenomena in terms of changeless principles. The principles of the Doxa offered a model for subsequent philosophies of nature, and provided the basis for theories of elements from the fifth century BC until today.