Plato and Platonism
(Originally appeared in The History of Science and Religion in the Western Tradition: An Encyclopedia. New York: Garland Publishing, Inc., 2000. pp. 109-14.)

Plato's (427-347 BCE) written work consists almost entirely of dialogues, all of which survive. He began writing soon after 399 BCE (when Socrates was put to death); the latest dialogues, including the unfinished Critias, were probably written in the last years of his life.

The status of his influential Athenian family would have made a career as a statesman or politician a natural one for Plato. Several events kept him from making this choice, however: the oligarchic revolt of 404, the trial and death of Socrates, and three disastrous voyages to Sicily (387, 367, and 361) in which Plato's political naivetÃ© nearly cost him his life. Plato showed no aptitude for, or much personal interest in, active political life. The contrast between the political and philosophical lives, and the stakes involved in choosing between them, are prominent themes in the dialogues (e.g. Gorgias, Republic, Theaetetus).

Soon after Socrates' death in 399 BCE, Plato apparently left Athens for Megara, where he visited Euclides (450-380), founder of the Megarian school; Cyrene, where he visited the mathematician Theodorus (ca. 460-390); and Italy, where he visited the Pythagorean Philolaus (ca. 470-390). Some sources suggest that Plato traveled also to Egypt. The object of Plato's travels appears to have been to establish contact with thriving scientific and mathematical communities. Already in his late twenties Plato showed an abiding interest in the science and mathematics of his day, and perhaps as a result of his travels he was able to draw accomplished scientists and mathematicians (notably Theaetetus [414-369], Eudoxus of Cnidus [390-340], and Heraclides of Pontus [390-310]) into his circle.

Among intellectual influences on Plato the most important was undoubtedly Socrates, from whom Plato learned the importance of definitional questions and the value of "discussion" (dialektikÃª). In addition, Plato showed himself to be well aware of the Sophists, especially their relativism and the opposition between nature (phusis) and law (nomos). He drew on Heraclitus (540-480 BCE) and his followers for the view that perceptible things are constantly changing. From Parmenides (515-440) and the Eleatic school Plato saw more clearly the problems attendant on the notion of change, the differences between "being" and "becoming," and the need to employ reasoning, not perception, in constructing adequate accounts of the world. This lesson Plato also learned from contemporary medical writers. Pythagorean mathematical discoveries confirmed the value of reasoning, the centrality of number and measure, and the importance of systematic organization of inquiry; Plato also drew on Pythagorean religious views such as the immortality of the soul and the limitations of the body. The views of other presocratic writers such as Anaxagoras (500-428), Empedocles (ca. 492-432), and the atomists are evident in Plato's work.

Plato founded the Academy sometime after his return to Athens. It is impossible to date its beginning exactly, but the period 380-370 BCE seems likely. It was not the first academy; Antisthenes and Isocrates (445-360 and 436-338, respectively) had established schools in which rhetorical proficiency was the primary object. Unlike the practical emphasis of these schools, however, the purpose of Plato's Academy was from the start theoretical, and it is probably the first occurrence in the West of the sort of institution we now think of as academic. From the start the curriculum was diverse, involving Plato's mathematical and scientific colleagues and incorporating many of what we now think of as the liberal arts.

Most of the Platonic writings with scientific or cosmological import were written while Plato was head of the Academy. Their object may have been less to convey Plato's settled views than to provoke discussion or to stimulate research. Whatever their object may have been, the fact that Plato wrote dialogues with consummate dramatic skill and that he was deeply suspicious of writing as a vehicle for conveying understanding, must be noted at the outset. The probing tentativeness that is a hallmark of Plato's thought is missing from Platonism in most of its later incarnations.

In Book VII of the Republic Plato outlines an educational program for the philosopher-rulers of his model city. From a young age students are to study arithmetic, geometry, astronomy, and music. They must master these sciences before they are allowed to practice philosophy, much less to rule. What impressed Plato about these sciences is made clear in the central books of the Republic. Perception is of limited use in understanding the world: perceptible things and qualities are constantly changing, and our accounts of them are confused and contradictory. Genuine knowledge -- the sort that can withstand Socratic examination -- cannot be had of such things. So long as we rely on our senses and do not employ abstract and systematic reasoning (of which the best example is mathematics), the best we can hope for is opinion (doxa). Genuine knowledge or understanding (nous or epistÃªmÃª) requires a different kind of object, one that is stable and not susceptible to the sorts of confusing change that characterize perceptible things. These intelligible objects Plato calls Forms (eidÃª) or Ideas (ideai).

Throughout the dialogues Plato treats the existence of Forms as relatively unproblematic. They are evidently distinct from perceptible things; to what degree and in what ways they are separate from such things, and just how they are related to them, are less obvious from Plato's writings, which contain differing accounts of such matters. For example, Plato frequently speaks of perceptibles as compounds or mixtures of Forms; this suggests that Forms literally constitute the perceptible things around us. (In this he is following Anaxagoras, Empedocles, and some of the philosophically inclined medical writers of his day.) In other places Plato speaks of the Forms as paradigms or patterns and of perceptibles as imperfect instances, shadows or copies or reflections, of such paradigms. It is unclear whether this latter way of speaking about the Forms is intended to complement the former or to supplant it. In any case, these were matters of keen debate in the Academy. Plato's successor Speusippus (407-339 BCE) emphasized the transcendence of the Forms, assimilating them to Pythagorean numbers; Eudoxus emphasized the immanence of the Forms, treating them as physical ingredients in the perceptibles around us. Aristotle's (384-322) influential criticisms of the Forms must have been honed in these debates.

What is clear is that Plato thought that the Forms could solve a number of philosophical and scientific problems bequeathed by his predecessors. For example, perceptible things are unstable and unknowable (as Heraclitus and Parmenides and others held); but the Forms, which are intelligible and which can be grasped securely by reasoning, are knowable and can serve as the basis of true accounts. Perceptible things do appear differently to different people (as the Sophist Protagoras had noted); but if one grasps the underlying Forms, one can both avoid being taken in by conflicting appearances and explain why the appearances conflict in the first place. The Forms are epistemically reliable because they are ontologically secure; perceptible things are neither. Clarity and understanding can be found only among intelligible things.

Plato's most notable ventures into science all follow this route. For example, in the Timaeus Plato explains the apparently irregular wanderings of the planets as manifestations of underlying perfectly orderly circular motions. He reduces to order the apparently random transformations of earth, water, air, and fire by suggesting that the atoms of which everything is made are really combinations of right triangles. Equipped with such micro-level accounts he can explain the susceptibility of our bodies to disease, the efficacy of treatment, and the processes of sensory perception, respiration, and digestion.

The influence of the Timaeus on later scientific and theological thought is hard to overstate. Prior to the systematic re-introduction of Greek philosophical works to the Latin West in the twelfth and thirteenth centuries, Calcidius' Latin translation and commentary on the Timaeus (ca. 360 CE) was the only Platonic work widely known in the West. It is important to remember that Plato's ventures into science all serve a philosophical-ethical end. The universe is a kosmos, an organized and rationally accessible whole. It can be understood only because it is the product of intelligence, and intelligence always orders things for the best. This teleological emphasis is clear in very early dialogues (e.g. Gorgias), in those of Plato's middle period (e.g. Phaedo, Republic), and in those of his later years (e.g. Timaeus, Philebus, Laws). The presence in late dialogues of a divine craftsman or Demiurge may or may not have been intended literally (this too was a matter hotly debated in the Academy); but the central point, that the universe is intelligible because and to the degree that it is the product of intelligence, is undeniably Platonic.

Plato's forays into arithmetic, geometry, astronomy, and music, as well as his metaphysical and epistemological views, provided his Academic colleagues with a productive research program. Aristotle, associated with the Academy for the last twenty years of Plato's life, contributed, as did Menaechmus, Heraclides, and Eudoxus. The last of these was a mathematician of great importance; in addition to inventing methods for approximating areas and volumes under curves and a theory of proportion applicable to incommensurable as well as commensurable magnitudes, Eudoxus developed an elegant model of the universe based on the idea of concentric spheres. This model, refined versions of which dominated astronomy until the sixteenth century, may have been inspired by Plato (it is sketched in the Timaeus). According to an early source Plato set his Academic colleagues this problem: "By the assumption of what uniform and orderly motions can the apparent motions of the planets be accounted for?" It is impossible to know how actively Plato contributed to Academic developments in astronomy, geometry, number theory, and the like; but his abiding interest and inspirational role in such developments is clear.

In the decades after Plato's death the Academy, under Arcesilaus (ca. 300 BCE) and later Carneades (ca. 200), changed its emphasis from mathematics and science to a kind of skepticism, apparently in reaction to trends in Hellenistic philosophy. Little is known about the Academy during these years. The first centuries of the common era, however, saw the development of "Middle" Platonism in Athens, Alexandria, and elsewhere. This was an uneasy synthesis of a variety of influences: Aristotelian, Stoic, Pythagorean, Hebrew, Zoroastrian, and Gnostic among them. Plato's Forms were now conceived as Ideas in the mind of God, who is in turn an amalgam of Aristotle's prime mover and the God of the Hebrew and Christian scriptures; matter and soul were opposed; several "grades" of reality were distinguished; and genuine knowledge or understanding was often taken to require a divine "spark" or illumination. Hints of all of these views can be found in Plato's writings, especially when one is equipped with techniques of allegorical interpretation. Such techniques, routinely practiced on the Homeric epics as well as the scriptures, were now widely applied to philosophical texts.

The Alexandrian Jew Philo (ca. 30 BCE-45 CE) was heavily influenced by Middle Platonism, as were the early Christian apologists Justin Martyr (d. 165), Clement of Alexandria (d. 215), and Origen (185-254). All four writers used Middle Platonism -- especially the cosmology of the Timaeus -- to reveal the mysteries of the Genesis account of creation. Platonism, suitably understood, became an important ally of Jewish and Christian revelation. It is not hard to see why. Unlike Aristotle, who maintained the eternity of the world and the materiality of the soul, Plato's insistence on the immortality of the soul, the role of the Demiurge in creating and sustaining the world, and the necessity of teleological explanation, could be harmonized with what had been revealed about the world in the scriptures.

The Neoplatonist movement of the third century of the common era represents a further step toward systematization and synthesis. It too incorporated aspects of current anti-materialist schools, especially Platonism and Pythagoreanism. In the hands of Plotinus (205-270), Porphyry (232-305), and Iamblichus (250-325) Platonic views exerted a powerful influence on early medieval philosophy and theology. (This despite the fact that several Neoplatonists, especially in Athens, were bitterly opposed to Christianity.)

Plotinus, drawing on Platonic images and metaphors, posited an ineffable One as the basic constituent of the universe. From this One there arise, by a series of emanations, the Intellect, then the Soul, then Nature, and finally Matter. Corresponding to these emanations is a diminution in reality: Matter, which is inert unless acted on by mind, is hardly real at all. Adequate explanations even of material phenomena, then, must exhibit the workings of the non-material world of mind.

The rise of Middle- and Neoplatonism corresponds with the decline of Greek science, the displacement of original research by a tradition favoring commentary and compendia, and the growth of Christianity as an intellectually respectable alternative to paganism. Not all Fathers of the Church were congenial towards pagan (i.e., Greek) philosophy, but most found ways to accomodate Plato and Platonism. Augustine (354-430) studied Neoplatonism just prior to his conversion to Christianity, and many of his most important works attempt to reconcile the best insights of the Platonic tradition with the truths of Christianity.

Three Neoplatonist writers of late antiquity deserve special mention for their scientific contributions. Proclus (410-485), head of the Academy at Athens and critic of Christianity, wrote long commentaries on Euclid's Elements, and on Plato's Parmenides and Timaeus, and an influential treatise, the Elements of Theology. These works are among our most valuable sources of knowledge concerning ancient mathematical and scientific theory and practice. Simplicius (d. 540) wrote lengthy and learned commentaries on most of Aristotle's works, drawing on presocratic and Hellenistic works in an attempt to reconcile the systems of Plato and Aristotle. John Philoponus (d. 570), an Alexandrian Christian and staunch anti-Aristotelian, also wrote commentaries on Aristotelian works, as well as other polemical treatises, including an attack on Proclus. His object was to show the defects of Aristotle's system (and the superiority of the Christian-Neoplatonic one). His trenchant criticisms of Aristotelian dynamics are a striking anticipation of later medieval and early modern attacks on Aristotle. Especially in the work of Simplicius and Philoponus we can see original scientific work of undeniable importance.

Soon after the Islamic conquest of western Asia in the seventh century, Muslim scholars encountered Greek philosophy. By the ninth century large numbers of Greek philosophical and scientific texts had been translated into Arabic -- works of Plato, Aristotle, Galen, Hippocrates, Euclid, and Ptolemy, among others. Plato's views, especially those of the Timaeus, attracted Islamic theologians for the same reasons they had attracted Christian ones. Since many of the Arabic writers whose philosophical views were most influential were also physicians or scientists, the Timaeus is especially important. Among those most clearly influenced by Platonism are the mathematician al-Kindi (800-870), the musical theorist al-Farabi (873-950), and (as a critic) ibn Sina (Avicenna) (980-1037). Later Islamic philosophical and scientific developments appear to owe more to Aristotelian traditions than Platonic ones.

The revival of learning in the Latin West during the twelfth century kindled a renewed interest in Greek and Latin texts. Although attention was largely devoted to grammar and rhetoric, Plato's Timaeus, together with Calcidius's commentary, inspired a number of significant and original thinkers. Two deserve special mention. In his Treatise on the Six Days of Creation, Thierry of Chartres (fl. 1140) attempted a detailed accomodation of the biblical account of creation to that given in the Timaeus. William of Conches (1080-1160) wrote long commentaries on the Timaeus and the book of Genesis, and an influential treatise, The Philosophy of the World, with a similar aim. Both thinkers offered and defended mechanisms by which God's creative purposes were achieved -- they invoked processes such as heating and cooling, evaporation and condensation, together with the natural motion of the four elements, to account for the sequence of events following God's initial creative act in the Genesis story. Drawing on Platonic and Stoic views, these thinkers distinguished between what is created directly by God and what results from interactions among things God has endowed with causal properties of their own. These properties (the "natures" of things) can be studied on their own, without appeal to God's activity. And, because of the close relations between macrocosm (the universe) and microcosm (individual person), human beings too must be seen as part of this natural order, and should be studied accordingly. This naturalistic perspective -- which accounted for the efficacy of astrology and theurgy as well as scientific inquiry -- held obvious dangers for orthodoxy, but they were partially offset by the insistence that the natural order was itself a product of God's handiwork.

The value of Platonic stock fell considerably in the late twelfth and thirteenth centuries as a result of the systematic translation of the Aristotelian corpus into Latin. Among the earliest Aristotelian works translated were those with scientific ramifications: Physics, On the Heavens, Meterology, On Generation and Corruption. The "likely story" of Plato's Timaeus was no match for Aristotle's rigorous and detailed cosmological treatises. Further, the scope and interconnectedness of the Aristotelian corpus was well suited to the setting of the new universities.

The new interest in Aristotelian natural philosophy had its benefits as well, however. For not only were the Aristotelian texts made available in translation; many of the ancient commentaries were as well. Some of them, e.g. those of Simplicius and Philoponus, contained valuable information about early Platonism as well as presocratic forerunners. The availability of these commentaries provided a much fuller picture of Platonic claims and arguments and their context than had previously been available. It became possible, for the first time in more than a thousand years, to begin to distinguish Plato's own opinions from those of the later traditions that grew up around them.

Plato's writings never disappeared from the curriculum altogether (in a famous remark Petrarch [1304-1374] suggests that "More men praise Aristotle; the better ones, Plato"). While the Platonic cosmology typically yielded to the Aristotelian when the two diverged, it had the virtues of affirming God's role as creator and the creation of the world in time and of not suggesting a rigorously deterministic world. Of the thirteen propositions condemned in 1270 by the Bishop of Paris, and the 219 condemned in 1277, the vast majority were of Aristotelian, not Platonic, provenance.

Platonic influences are not hard to find in thirteenth-century Oxford natural philosophy. Robert Grosseteste (1169-1253), like the Chartres Platonists of the twelfth century, put Platonic and Neoplatonic metaphysical ideas to "scientific" use. Borrowing Neoplatonist images of light (which in turn drew on Platonic similes, e.g. the Sun in Republic V), Grosseteste suggested that the propagation of light was the key to understanding God's creative activity. Both Grosseteste and Roger Bacon (1213-1291) drew from Platonic and Aristotelian sources in developing their distinctive views on scientific methods, the place of mathematics in the study of nature, and the relations between scientific and theological inquiry.

Nevertheless, throughout the thirteenth and fourteenth centuries Aristotle's importance waxed as Plato's waned. It was not until the fifteenth century, and the growth of humanistic learning outside the university, that Plato's writings recovered some of their former currency. For example, among Italian humanists Plato's writings were initially prized for their literary and dramatic qualities; it was not until the late fifteenth century, with the Christian Platonism of Nicholas of Cusa (1401-1464) and Marsilio Ficino (1433-1499), that the philosophical and cosmological richness of the Platonic tradition regained some of its former place. Nevertheless, Plato's works were repeatedly translated in the fifteenth century, and in 1484 Ficino published a complete edition of the Platonic dialogues in Latin. These translations and the lengthy commentaries Ficino wrote to accompany them were widely used in the early modern period.

The new mechanistic philosophy of the early seventeenth century provoked a resurgence of interest in Platonism at Cambridge. Among the so-called "Cambridge Platonists" Ralph Cudworth (1617-1688) and Henry More (1614-1687) invoked Platonic images and arguments against Hobbesian materialism and Cartesian mechanism. By emphasizing the need for contemplation and illumination, the Platonism of Cudworth and More contributed to an effort to unify an English Church riven by decades of bloody faction.

Of the major figures in the Scientific Revolution the most clearly indebted to Plato is Johannes Kepler (1571-1630). Kepler's most important cosmological works owe their inspiration and many of their basic principles to the Timaeus. Kepler's underlying conviction -- that there must be elegant mathematical laws underlying the apparently anomalous planetary motions -- is certainly Platonic and Pythagorean. (It gave rise to Kepler's relatively sober three laws of planetary motion as well as his fanciful speculations about the arrangements of the planetary orbits.)

From the early days of the Academy Platonism has meant different things to different people, and it has frequently been defined in opposition to other views. In part this is because Plato articulated many of his own positions in the course of polemics against other views. Yet the positive doctrines of Platonism -- the emphasis on teleology and on non-material aspects of explanation, the insistence on the inadequacy of perception and connection between the intelligible and the real, and the faith that there is order and reason at the heart of things -- have been and continue to be a vital force in the philosophical, scientific, and religious thought of the western tradition.

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