(b. Caesarea [?], late fifth century; d. Alexandria, second half of sixth century)
Most of what is known about Philoponus is found in a few remarks made by him and by some of his contemporaries. He gives the dates of two of his books: his commentary on Aristotle’s Physica was written in 517 and his book against Proclus in 529. One of his last works, De opificio mundi, was dedicated to Sergius, who was partriarch of Antioch from 546 to 549. Philoponus was one of the last holders of the chair of philosophy in Alexandria, succeeding Ammonius the son of Hermias. His Philosophical background was Neoplatonic; but he was—probably from birth—a member of the Monophysite sect, which was declared hertical in the seventh century.
Philoponus’ main significance for the history of science lies in his being, at the close of antiquity, the first thinker to undertake a comprehensive and massive attack on the principal tenets of Aristotle’s physics and cosmology, an attack unequaled in thoroughness until Galileo. the essential part of his criticism is in the commentary on Aristotle’sMeteorologica, in his book De aeternitate mundi contra Proclum, and in excerpts from his book against Aristotle’s doctrine of the eternity of the world. This last work has been lost, but Philoponus’ pagan adversary Simplicius quoted from it extensively in his commentaries on Aristotle’s Physica and De caelo.
Philoponus’ philosophy of nature was the first to combine scientific cosmology and monotheism. The monotheistic belief in the universe as a creation of God and the subsequent assumption that there is no essential difference between things in heaven and on earth, as well as the rejection of the belief in the divine nature of the stars, had already been expressed in the Old Testament and was taken over by christianity and later by Islam. The unity of heaven and earth had been accepted as a fact, but Philoponus was the first to interpret it in the framework of a scientific conception and to explain it in terms of a world view differing from myth or pagan beliefs. His point of departure was a criticism, supported by physical arguments, of Aristotle’s doctrine of the eternity of the universe and the invariable structure of the celestial region. The physical basis of Aristotle’s dichotomy of heaven and earth was his assumption that the celestial bodies are made of the indestructible fifth element, the ether. As early as the first century B. C. an attack on the concept of ether was made by the Peripatetic philosopher Xenarchus. His book Against the Fifth Element is lost, but frangments are extant in quotations by Simplicius in his commentary on Aristotle’s De caelo. No doubt Xenarchus’ book was also known to Philoponus; but from a remark by Simplicius it appears that Philoponus’s arguments against the ether went much further than those of Xenarchus, particularly those concerned with his physical proofs in favor of the fiery nature of the sun and stars. Aristotle had claimed that “the stars are neither made of fire nor move ikn fire” (De caelo, 289a34) and that the celestial stuff “is eternal, suffers neither growth nor diminution, but is ageless, unalterable and impassive” (ibid., 270bI). Heat and light emitted from the celestial bodies are produced, according to him, by friction resulting from their movements, a case similar to that of flying projectiles. This is what makes us think that the sun itself possesses the quality of fire, but even the color of the sun does not suggest a fiery constitution: “The sun, which appears to be the hottest body, is while rather than fiery in appearance” (Meteorologica, 314a 36).
Philoponus denied Aristotle’s statement regarding the color of the sun and emphasized that the color of a fire depends on the nature of the fuel: “The sun is not white, of the kind of color which many stars possess; it obviously appears yellow, like the color of a flame produced by dry and finely chopped wood. However, even if the sun were white, this would not prove that it is not of fire, for the color of fire changes with the nature of the fuel” (In Meteorologica, 47, 18).
Philoponus expressed this idea elsewhere, explicitly comparing celestial and terrestrial sources of light: “There is much difference among the stars in magnitude, color, and brightness; and I think the reason for this is to be found nothing else than the composition of the matter of which the stars are constructed. . .. Terrestrial fires lit for human purpose also differ according to the fuel, be it oil or pitch, reed, papyrus, or different kinds of wood, either humid or in a dry state” (De opificio mundi, IV, 12). If the different colors of the stars indicate their different constitutions, it follows that stars are composite bodies; and since composite things imply decomposition and things implying decomposition imply decay, one must conclude that celestial bodies are subject to decay. But, Philoponus argued, even those who believe the stars to be made of ether must assume them to be composed of both the matter of the fifth element and their individual form, different for each star. “However, if one abstracts the forms of all things, there obviously remains the three- dimensional extension only, in which respect there is no differnce between any of the celestial and the terrestrial bodies “(Philoponus, apud: Simplicius, In Physica 1331, 10). Thus, anticipating Descartes, Philoponus arrived at the conclusion that all bodies in heaven, as well as on earth, are substances whose common attribute is extension. Against the objection raised by Simplicius that no change can be observed in the celestial bodies, Philoponus adduced arguments from physics, stressing that the greater the mass of a body, the slower its rate of decay. Furthermore, the slowness of change is a function not only of the mass but also of certain physical properties, such as hardness; moreover, it is well known, for instance, that different animals have different life spans and that some parts of them are more resistant than others to change.
The monotheistic dogma of the creation of the universe ex nihilo by the single act of a God who transcends nature implied, for Philoponus, the creation of matter imbued with all the physical faculties for its independent development according to the laws of nature, a development according to the laws of nature, a development that he conceived of as extending from the primary chaotic state to the present organized structure of the universe. This deistic conception of a world that, once created, continues to exist automatically by natural law, was completely foreign to the classical Greek view, which never considered the gods to be “above nature” but associated them with nature, reigning not above it but within it. The shock created by this conception of Philoponus’ is reflected in the words of Simplicius, who is bewildered by the idea of a god who acts only at the single moment of creation and then hands over his creation to nature.
Philoponus’ anti- Aristotelian views were not restricted to problems of cosmology and to the removal of the barriers between heaven and earth. He also took strong exception to some of the main tenets of Aristotle’s dynamics. According to Aristotle, movement is not possible without a definite medium in which it can take place; thus, statements on the movement of bodies must always be related to a certain medium. Aristotle asserted, for instance, that in a given medium the velocities of falling bodies are proportional to their weights, and that the velocities of a given body in different media are inversely proportional to the densities of these media. Furthermore one of the many reasons given by Aristotle for denying the existence of a void was that it would be like a medium of zero density; and thus the velocity of a falling body in vacuo would reach infinity, regardless of its weight. Philoponus, in opposition to Aristotle, did not exclude the feasibility of movement in a void. However, against the view held by the Epicureans (proved to be correct), he assumed that in the void Aristotle’s law of the proportionality of the velocities and weight of falling bodies would be exact. Against Aristotle he stressed that the impeding influence of a medium on a falling body consists in an additional increase of the body’s time in motion over and above that of the natural motion in vacuo depending on the density of the medium. This additional time will be directly proportional to the density of the interfering medium. In a lengthy argument Philoponus refuted Aristotle’s statements and emphasized that experience shows that “if one lets fall simultaneously form the same height two bodies differing greatly in weight, one will find that the ratio of their times of motion does not correspond to the ratio of their times of motion does not correspond to the ration of their weights, but that the difference in time is a very small one” (In Physica, 683, 17).
Philoponus had his doubts about the essence and the causes of the natural motion of light and heavy bodies. For instance, he wrote that one cannot agree with Aristotle that air tends to move only upward. Air may move downward for some physical reason, such as the removal of earth or water beneath it; in this case it will rush down, filling the void thus created. On the other hand, it may well be that the socalled natural motion upward has a similar cause, if there happens to be an empty space in the upper region.
Of special importance is Philoponus’ criticism of Aristotle’s theory of forced motion. He rejected the main contention of the Peripatetic that in every forced motion there must always be an immediate contact between the mover and the body forced to move in a direction other than that of its natural motion. In particular Philoponus denied Aristotle’s hypothesis that besides the push given to a missile by the thrower, the air behind the missile is set in motion and continues to push it. He argued convincingly that if string and arrow, or hand and stone, are in direct contact, there is no air behind the missile to be moved, and that the air which is moved along the sides of the missile can contribute nothing, or very little, to its motion. Philoponus concluded that “some incorporeal kinetic power is imparted by the thrower to the object thrown “and that” if an arrow or a stone is projected by force in a void, the same things will happen much more easily, nothing being necessary except the thrower” (ibid, 641, 29). This is the famous theory of the impetus, the precursor of the modern vectorial term “momentum” or scalar term “kinetic energy.” The impetus was rediscovered by Philoponus 700 years after it had been conceived of by Hipparchus (see Simplicius, In De caelo, 264, 25) In the physics of medieval Islamic philosophers and Western Schoolman the concept of impetus was developed further, mainly as a consequence of a tradition folling Philoponus.
Philoponus returned to his idea of the impetus in his anti- Aristotelian theory of light, which he developoped in the guise of an interpretation of Aristotle’s doctrine that centers on the basic categories of potentiality (dynamis) and actuality (energeia). According to Aristole, light is the state of actual transparency in a potentially transparent medium; by such an actualization any potentially colored body found in this medium becomes actually colored and thus visible. Light is therefore a static phenomenon whose emergence and disappearance are instantaneous and have nothing to do with locomotion. Philoponus raised the fundamental question of how Aristotle’s view can be compatible with both the laws of geometrical optics, developed in the Hellenistic period, and the thermic effects of light, which are so strongly enhanced by its concentration through burning glasses. He emphasized that light must be a directional phenomenon and that visual rays move in straight lines and are reflected according to the law of equal angles. However, at the same time he pointed out that these rays are not projected from our eyes to the luminous object, as was formerly assumed, but that they move in the opposite direction, from the luminous object to the eye. He clearly stated the principle of reversibility of the path of light for the case of reflection: “It makes no difference whether straight lines proceed from the eye toward the mirror or whether they are reflected from the mirror toward the eye” (In De anima, 331, 27). Making this assumption, Philoponus interpreted Aristotle’s term energeia (actuality) as a kinetic phenomenon proceeding from the luminous object to the eye. He attempted to reconcile Aristotle’s conception of light as actualization of a state with geometrical optics by identifying the visual rays with the energeia light, interpreting energeia as “force” and conceiving the emission of light in terms of the doctrine of impetus. Light is “an incorporeal kinetic force [energeia kinetikē] emitted from the luminous object, similar to the force imparted by the thrower to the body thrown (In Physica, 642, 11)
Even when Philoponus accepted Aristole’s tenets, he was most remarkable in the originality and ingenuity of his exposition or amplification of Aristotle’s physical doctrines. Sometimes he posed questions never raised before, anticipating much later developments; and some of the solutions he offered are evidence of the great acuity of his mind. Conspicuous examples are his discussion of the functional dependence of one set of variable quantities on another and his clear recognition of the course of a function —in modern language its first derivative. Assuming with Aristole that the physical properties of a substance ultimately depend on the mixture of the four elementary qualities— hot, cold, dry, and moist—he asked how a reasonable explanation can be given of the fact that one of the physical properties of a given substance may remain practically unaltered while the other is undergoing a visible change. Two examples are the sweetness of honey remaining constant while its color changes from yellow to white and the color of wine remaining the same while its taste changes to sour. If all the properties derive from the primary qualities, one should expect them to change together with the qualities. Philoponus’ answer is given in what can be defined as a verbal description of a graphic representation (unknown before the late Middle Ages). He explained that every physical property is a variable depending on the four primary qualities, so that if the qualities are diminishing, the physical properties are also being reduced. However, the rate of change is different for each of the properties; and thus, “if the mixture of the independent variables is slightly varied, the sweetness of the honey, e. g., will not alter appreciably, but its color may change completely” (In De generatione et corruptione, 170, 32).
Another very acute remark of Philoponus’ is his comment on Aristotle’s statement in the Physica that “all things that exist by nature seem to have within themselves a principle of movement and of rest” (Aristotle, Physica, 192b13). Many Aristotelian commentators have pondered the question of how to include the heavens in this definition of nature, since they are never at rest but move eternally in a crcle. Philoponus answered this question by interpreting the uniform and circular motion of the celestial bodies as inertial motiom: “rest is found in all things. For the perpetually moving heavens partake in rest, because the very persistence of perpetual motion is rest” (In De anima, 75, 11). Elsewhere he repeated his definition of inertial motion, adding that “the celestial bodies are, if I may say so, motionless in their motion” (In Meteorologica, 11, 31).
The concepts of potentiality and actuality, which Aristotle used extensively in his physical treatises, were occasionally supplemented, from the second century on, by a term expressing the capacity of a body to actualize a certain property or state that exists only potentially. The Greek word for this was epitedeiotes, meaning “fitness,” “appropriateness,” or “suitability”, it was sometimes used as a synonym for potentiality but later came to signify the sufficient condition for actuality, thus restricting potentiality to a necessary condition for actuality. In several of his writings Philoponus makes frequent use of this meaning of “fitness,” occasionally in order to amplify Aristotle’s doctrine of the basic requirements for physical action, whereby it is supposed that both the thing acting and the thing acted upon must be alike in kind but contrary in species. One of the examples given by Aristotle is the change of color, which he regarded as a process in which the object acted upon changes into the acting object by assimilation. Philoponus, commenting on this, remarked that such processes require the fitness of the active object to accomplish the assimilation. The black ink of a cuttlefish, he said, will overpower the whiteness of milk; but the black of a piece of ebony, when put into the milk, will not affect its color because of its lack of fitness. In the same way, brass or silver or silver metals will resound for some time after having been struck—i.e., they are capable of turning potential sound into actual sound—because they have a fitness for producing sound, in contrast with wood or other nonmetallic substances.
On anothor occasion philoponus made use of the concept of fitness in order to defend against Aristotle’s criticism Plato’s doctrine of the soul as the mover of the body. Aristotle in his De anima argued that if Plato were right, it would be possible for the soul that had left the body to enter it again, and thus resurrection of the dead could be feasible, although it had never been observed. Philoponus emphasized that the soul keeps the body moving only so long as the body has the mechanical fitness to be worked on, and it loses that fitness when death occurs. Characteristically, he adduced mechanical similes for his view: “A stick pushed against a door cannot move it when it has not the fitness necessary for being moved.. It will not do so when fastened by nails or when the hinges are loose. Everything set in motion by something else generally needs a certain specific fitness” (In De anima, 108, 24). One interesting aspect of Philoponus’ treatment of this problem is the way in which, anticipating Descartes, he looked at the human body as a mechanism capable of functioning only if its parts have the necessary mechanical fitness.
Philoponus’ Neoplatonic background, depending largely on Stoic conceptions, is also evident in his manner of discussing a problem that in modern terms can be defined as resonance; it also shows his keen powers of observation. He described the ripples produced in the water in a metal cup when the cup is brought into a state of vibration. He assumed that these vibrations are not transferred directly to the water but that the air enclosed in the metal acts as an intermediate agent. This assumption shows influences of the Aristotelian theory of metals (Meteorologica, III, 6) as well as of the Stoic doctrine of pneuma.
If we pass a wet finger round the rim [of the cup], a sound is created by the air squeezed out by the finger, which air is ejected into the cavity of the cup, producing the sound by striking against the walls. Experimental evidence for it can be brought in the following way: If one fills a cup with water, one can see how ripples are produced in the water when the finger moves round the rim [In De anima, 355, 34].
If the cup itself is held by the hand, no sound is produced, because, as Philoponus explained, “the body struck must vibrate softly, so that the air . . . is emitted continuously into the upper part, striking the walls of the cup and being reflected toward all of its parts” (ibid.).
A very ingenious physical illustration was given by Philoponus to explain the perturbation of a system by external forces. He discussed the Aristotelian concepts “according to nature” and “contrary to nature” in the context of explanations given of an illness or a congenital deformity. Such phenomena, according to his view, have to be regarded in a wider framework, as parts of a whole, in order to be considered natural. This is basically the Stoic idea that if something goes wrong, the event or object in question must be seen as a partial phenomenon. In the framework of a wider system, taken as a totality, the wrong is compensated in some way and the harmony of the whole is restored. Philoponus introduced a more physical notion into this trend of thought. When something “coutrary to nature” happens to a physical object, one has to regard it as a perturbationcaused by outside factors. The intervention restores the phenomenon as a “natural” one, as something in accordance with nature. Part of Philoponus’ example is worth quoting:
I will give you an illustration that will explain what happens with things contrary to nature: Suppose that a lyre player tunes his instrument according to one of the musical scales and is then ready to being his music.. . . Let us assume for the sake of this illustration that the strings are affected by the state of humidity of the environment and thus get out of tune. . . . strikes the lyre, the substance of the strings does not perform the melody that he had in mind; but instead an unmusical, distroted, and indefinite sound is produced [In Physica, 201, 28].
Philoponus then went on to say that the harmony of the whole is restored by taking into account the climactic changes and the perturbation of the strings caused by them.
On several occasions Philoponus discussed the problem of the infinite. He rejected the use of the infinite in the sense of the unlimited in extension;and in his rejection he went even further than Aristotle, not and only denying, as Aristotle did, the existence of the infinite as an actual entity but also excluding the potentially infinite. Aristotle had admitted the possibility of entities that can be increased in infinitum without ever reaching actual infinity, but he did this mainly in order to reconcile his doctrine of the eternity of the universe and the infinite duration of the human race with the concept of infinity.
From his opposite position, believing in the beginning of the world at a finite point in the past, Philoponus argued that acquiescence in the existence of the potentially infinite will perforce lead to the admission of the actually infinite. Once one admits the infinite as a never- ending process, he said, the existence of an infinite magnitude existing by itself, or of a number that cannot be passed through to the end, cannot be excluded. From this, in his view, obvious absurdities would follow. A few sentences from his argument may be quoted here:
If the universe were eternal, it is obvious that the number of men up to now would be infinite, i.e., actually infinite—since obviously they all have actually come into existence—and thus an infinite number would be possible. For if all human individuals have become actual up to now—and we, for instance, will be the limit of the actually infinite number of men who have been before us—then the infinite will actually have been passed through to the end [In Physica, 428, 25].
Philoponus went on to say that if we extend this definite limit to a future generation, the infinite will be further increased:
This increase will tend toward infinity, if the universe is incorruptible, and thus the infinite will be infinitely increased.. . . For each generation, e.g., my own, will have been passed through to its end, and for something to be greater and more infinite than the infinite itself, it is impossible for time or for the universe to be eternal [ibid.].
Another argument of Philoponus’ against the eternity of the universe is worth nothing because it was later used by Simplicius (who wrote a polemic against it) from Philoponus’ lost work against Aristotle. Philoponus, by a reductio ad absurdum, set out to prove that a universe without a beginning would necessarily involve the existence of different actual infinities, representing the relative numbers of the revolutions of the planets:
Since the spheres do not move with equal periods of revolution, but one in thirty years, the other in twelve years, and others in shorter periods. . ., then necessarily Saturn must have revolved and infinity of times, more, the moon 360 times more, and the sphere of the fixed stars are more than 10,000 times as often. Is it not beyond any absurdity to sduppose a ten-thousandfold infinity or even an infinite time of infinity, while the infinite cannot be comprised even once. Thus necessarily the revolution of the celestial bodies must have had a beginning [Philoponus, apund: Simplicius, In Physica, 1179, 15].
This passage is of interest to the historians of mathematic, since Philoponus, although he rejected altogether the notion of the infinite, here, for the first time in a specific case, made use of infinite cardinal numbers, anticipating modern concepts by more than 1,300 years.
I. Original Works. Editions of Philoponus’ writings include In Physica, H. Vitelli, ed. (Berlin, 1887); In De anima, M. Hayduck, ed. (Berlin, 1897); In De generatione et corruptione, H. Vitelli, ed. (Berlin, 1897); De opificio mundi, G. Reichardt, ed. (Leipzing, 1897); In Categoria, A. Busse, ed. (Berlin, 1898); De aeternitate mundi contra Proclum, H. Rabe, ed. (Leipzing, 1899); In Meteorologica, M. Hayduck, ed. (Berlin, 1901); In Analytica priora, M. Wallies, ed. (Berlin, 1905); and In Analytica posteriora, M. Wallies, ed. (Berlin, 1909).
II. Secondary Literature. Editions of Simplicius’ works are In Physica, H. Diels, ed. (Berlin, 1882); and In De caelo, J. L. Heiberg, ed. (Berlin, 1894). See also A. H. Armstrong, ed., The Cambridge History of Later Greek and Early Medieval Philosophy (Cambridge, 1967), pp. 477- 483; E. Evrard, “Les convictions religieuses de Jean Philopon et la date de son Commentaire aux Mé té orologiques” in Bulletin de l’s Acadè mieroyale de Belgique, classe de letters, 6 (1955), 299 ff. “loannes Philoponus,” in Pauly-Wissowa, IX, cols. 1764- 1793; H. D. Saffrey, “Le Chré tien J. Philoponet la survivance de l’ ecole d’ Alexandrie,” in Revue des é tudes grecques,67 (1954), 396- 410; Walter Böhm, Johannes Philoponus, Ausgewählte Schriften (Munich, 1967); Michael Wolff, Fallgesetz und Massebegriff: zwei wissenschaftshistrorische untersuchungen zur Kosmologie des Johannes Philoponus (Berlin, 1971); and S. Sambursky, The Physical World of Late Antiquity (London- New York, 1962); and “Note on John Philoponus’ Rejection of the Infinite,” in Festschrift for Richard Walzer (Oxford, 1972)
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(b. Ceaserea [?] c. 490; d. Alexandria, c. 570),
natural philosophy, theology. For the original article on Philoponus see DSB, vol. 7.
Since the original publication of the DSB there have been large-scale changes in Philoponus’s studies in particular and late antique philosophy generally. Thanks in great part to the work of Richard Sorabji, Philoponus and other late antique thinkers have been the subject of numerous monographs and articles. And Sorabji’s large translation project of the Commentaria in aristotelem graeca and associated texts has led to the widespread availability of Philoponus’s writings for English-language scholars.
Known also as John the Grammarian or John of Alexandria, John Philoponus was one of the most astute philosophical thinkers of the sixth century. A Christian Neoplatonist adhering to the Monophysite sect, he spent his career articulating a reformed Aristotelian physics that he hoped would both be amenable to Christians yet would retain the marked rationalism of pagan philosophy. He was educated at the Academy in Alexandria under Ammonius Hermeiou and probably taught there, although he likely did not hold the chair of philosophy. His earliest works were traditional commentaries on Aristotle and other elementary texts, such as a treatise on the astrolabe and an introduction to Nikomachus’s Arithmetic. Philoponus’s name is attached to five commentaries (on the Categories, the Prior and Posterior Analytics, De anima, and De generatione et corruptione), which in fact were lectures given by Ammonius that Philoponus edited and to which he added some of his own ideas. Few works can be dated with precision, but his commentary on the Physics (which includes the important Corollary on Place and Corollary on Void) was published in 517. An unfinished commentary on the Meteorologica was written shortly thereafter.
Beginning in the late 520s, Philoponus wrote a number of important treatises aimed at refuting arguments for the eternity of the world. The two most important of these are Contra Proclum de aeternitate mundi and the now-fragmentary Contra Aristotelem de aeternitate mundi. His final natural philosophical work, De opificio mundi— an exegesis of the opening book of Genesis in an attempt to reconcile Christianity with pagan natural philosophy— was most likely written in the 540s, although other evidence points to a date ranging from 557 to 560. The remainder of his career was dedicated primarily to specifically Christian theological issues, yet he retained a belief in the possibility of solving questions of the trinity and the nature of Christ with the same pagan rationality that he applied to natural philosophy. Indeed, by rigorously applying the Aristotelian definition of substance to the problem of the trinity, Philoponus developed a theology that his opponents would brand Tritheism (the Godhead contains three individual substances) for which he was anathematized from the church about a century after his death in 681. Although his anathema all but eliminated his influence in the Latin Christian thought, he had an impact on Islamic philosophy (particularly his arguments against eternity), which then later contributed to Latin Christian thought through the translation movement of the twelfth and thirteenth centuries.
Although scholars used to celebrate Philoponus for his apparent anticipation of many ideas developed during the scientific revolution of the seventeenth century (for example Galileo’s impetus theory or Descartes’s theory of matter as extension), later scholars placed him squarely in the intellectual context of the sixth century. It cannot be denied that Philoponus did in fact take some strikingly modern positions, but viewed as a whole he was a man of late antiquity, albeit with exceptional intellectual talent. Moreover, although often portrayed as a potent warrior in the battle to overcome Aristotle’s towering influence on the history of Latin Christian thought, he nonetheless retained a deep admiration for and indebtedness to Aristotle and an even deeper admiration of the philosopher’s commitment to rationality. That is, one should not be deceived by Philoponus’s rejection of eternity or his attempt to unify heavenly and terrestrial physics, for example, into thereby believing that he rejected Aristotelianism altogether as would happen in the modern era. Basic Aristotelian principles—the four causes, the role of potentiality and actuality, substance and accident—were not only retained by Philoponus but were his central resources for developing a new Christian natural philosophy.
Nonetheless, John Philoponus was a reformer. He was inspired primarily by the desire to bring natural philosophy into line with Christian dogma. And the most sweeping and decisive reform was the polemical and philosophical attack against pagan philosophers’ arguments for eternity. The attacks were systematic and comprehensive, taking each of the many arguments for eternity and drawing out contradictions, absurdities, and philosophical difficulties. Some of the arguments Philoponus deployed were not original, but he also presented many novel and fascinating ones. Aristotle rejected actual infinites as a general rule (e.g. infinite extension). This is one of the major tenets which Philoponus exploited to show that eternity entails actual infinites (e.g. an infinite number of past generations) and thus violates Aristotle’s own criteria. He asked how there could be different numbers of infinites: Different planets rotate around the earth at different rates and so there has been one actual infinite number of rotations for Jupiter and another for Mars, an early instance of cardinal numeration of infinites. Philoponus also challenged eternity from the opposite perspective, pointing out the unactualizable character of eternities. If the future is infinite, then its potential will never be exhausted and thus an eternal future violates the principle of plenitude: A potentiality which is never actualized is not a true potentiality at all. Philoponus also articulated another problem with the supposed eternity of the cosmos, namely, how could a finite body like the heavens continue eternally without an infinite force to keep it in motion? But a finite body cannot contain an infinite force, so its existence must be limited. These brief examples by no means represent the full extent of Philoponus’s powerful anti-eternity polemics, but they do give particular insight into the way in which he turns the pagans’ own philosophical resources against them.
Philoponus also rejected the existence of Aristotle’s fifth element, the aether. As a Christian, he denied the heavens were divine or endowed with intelligence and argued that they were composed of the traditional terrestrial elements. The heavens manifestly have some terrestrial qualities—like the sun’s heat—regardless of the protestations of pagans to the contrary. He dissented from Aristotle’s problematic theory of forced motion, attempting instead to develop an impetus theory. Further he suggested that the heaven’s circular motion was not the natural motion of the aether but a forced motion imparted to them by the Creator at the beginning of the world, just as the motion of the sphere of fire (directly below the Moon and in which meteorological phenomena occur) is forced, according to the pagans, because its circular motion is not natural but imparted to it by the celestial spheres. Consequently, because all forced motions eventually end, so too will the rotation of the heavens. He also defined place, again rejecting Aristotle, as the empty three-dimensional space which a body occupies. This theoretical void space never exists without body because of nature’s horror vacui, but qua empty can be subjected to thought experiments about how it might behave if it were in fact void space.
Philoponus’s reformed natural philosophy was deeply controversial. Simplicius, his pagan counterpart at the Athenian Neoplatonic Academy, was scathing in his response to Philoponus’s Contra Aristotelem. Simplicius saw it not only as philosophically disingenuous (to be fair, some arguments are) but also as a betrayal of pagan religion and its sacred race. And some Christians, particularly those from the diphysite Nestorian sect such as Cosmas Indicopleutes, objected just as vociferously. Cosmas argued that Christians should reject paganism entirely, including the tradition of Greek philosophical rationalism. For him, Philoponus’s main fault lay in his failure to refer to scripture as a guide to forming a Christian natural philosophy. Philoponus responded with his De opificio mundi, an exegesis of the narrative of creation and fierce pro-rationalist polemic against Cosmas’ provincialism and ignorance. Despite his controversial role, he steadfastly considered himself a champion of reasonable Christianity (he entitled his proposed solution to the doctrinal controversies surrounding the Second Council of Constantinople  the Arbiter) and created a comprehensive and coherent, if ultimately unsuccessful, alternative to the dominant Aristotelian natural philosophy of Late Antiquity.
WORKS BY JOHN PHILOPONUS
Ioannis Alexandrini cognomine Philoponi De usu astrolabii eiusque constructione libellus. Edited by Heinrich Hase. Bonnae: E. Weberi, 1839.
Ioannou Grammatikou Alexandreos (tou Philoponou) eis to proton tes Nikomachou Arithmetikes eisagoges. Edited by Richard Hoche. Lipsiae: Teubner, 1864.
Carte archéologique de la Gaule. Vols. 13–17 (1887–1909).
De aeternitate mundi contra Proclum. Edited by H. Rabe. Lipsiae: Teubner, 1899.
Against Aristotle, on the Eternity of the World. Translated by Christian Wildberg. Ithaca, NY: Cornell University Press, 1987.
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———. Aristotle Transformed: The Ancient Commentators and Their Influence. London: Duckworth, 1990.
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"John Philoponus." Complete Dictionary of Scientific Biography. . Encyclopedia.com. (October 19, 2017). http://www.encyclopedia.com/science/dictionaries-thesauruses-pictures-and-press-releases/john-philoponus-0
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