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Buridan, John

[Biographical Encyclopedia of Astronomers, eds. T. Hockey et al.,
Springer, 2014, pp. 341-343.]

ca. 1300-1358/1361


John Buridan was one of the most influential philosophers of his time, who, after William Ockham, was primarily responsible for the emergence of the nominalist via moderna, the “modern way” of dealing with theoretical matters, contending with the realist via antiqua (“the old way”) in late medieval universities. Despite this fact, we know relatively little about his life. He was born around 1300 somewhere in the diocese of Arras, in Picardy. He was probably the son of a poor family, which is indicated by the fact that he completed his early education in the College of Cardinal Lemoine, where he may have been a recipient of a stipend for needy students. He obtained his license to teach sometime after 1320 at the Arts Faculty of the University of Paris, where he taught for the rest of his life as Master of Arts. Given the usual career path of university professors of the time, who, after some teaching at the “undergraduate” Arts Faculty, usually promptly moved on to the “graduate schools” of Law, Medicine, or Theology, the fact that he stayed at the Arts Faculty is significantly non-typical, and may indicate a deliberate, prudent choice on Buridan’s part. In any case, it is quite likely that in this professional setting he could more securely carry out his program of a “quiet nominalist revolution”. (In fact, the claim that the plain nominalist doctrine was easier for young students to understand than the abstruse realist doctrine was one of the main arguments of later nominalist Masters of Art who petitioned the university of Cologne in 1425 to exclude the via antiqua from the Arts curriculum -- the administration rejected the petition. See Ehrle, p. 282.) Nevertheless, the fact that Buridan did not move on to any of the higher faculties did not diminish his professional stature. He was twice elected rector of the University of Paris, in 1327/8 and 1340, and became a highly respected, influential public figure of his time. He was unusually well-off for a university professor, drawing income from at least three benefices. His students, radiating from Paris to the newly established universities of Europe (some of them actively participating in the process of university-foundation, acting as first rectors) widely disseminated his nominalist doctrine, and made it part of their curricula. Buridan may have died already in the plague of 1358, but he certainly did not live after 1361, when one his benefices went to another person.

In accordance with the requirements of philosophy teaching of the time, Buridan’s works -- besides some independent treatises in logic (in particular, the Treatise on Consequences, and the monumental Summulae de Dialectica) -- primarily consist of running commentaries and question-commentaries on Aristotle’s works, ranging from logic to metaphysics, to natural philosophy, to ethics, and politics. The question format, raising and thoroughly discussing major problems in connection with Aristotle’s text, allowed Buridan to develop a comprehensive nominalist philosophical system, putting to consistent use the analytic conceptual tools he worked out in his logical treatises.

These conceptual tools allowed Buridan to provide meticulous analyses of the technical language of Aristotelian science without the ontological commitments of traditional medieval Aristotelianism. But besides securing the parsimonious ontology required by his nominalism, Buridan’s conceptual analyses also enabled him to tackle traditional scientific problems in innovative ways. Thus, for instance, his logical theories of connotation and appellation, coupled with his theory of truth-conditions for tensed propositions, allow him to present an analysis of time as being simply the number of the revolutions of the sphere of the fixed stars connoted in various ways by our concepts having some temporal connotation. This of course does not mean that time is a matter of subjective experience, since the revolutions of the outermost sphere are real regardless of whether there is a human mind to count them. Still, this number is only time if it is connoted by appropriate temporal concepts: as Buridan put it, were there no human minds forming concepts with such a connotation, the thing that is time would still exist, but it would not be time.

But aside from the incisive conceptual analyses Buridan provided within the paradigm of Aristotelian natural philosophy, his most lasting contribution to physics in general, and to astronomy in particular, was his theory of impetus, which had a significant role in eventually dismantling that paradigm.

Buridan primarily introduced the notion of impetus to account for a particular puzzle of Aristotelian physics, namely, the motion of projectiles. The puzzle was generated by the commonly accepted principle that whatever is in motion needs a mover to sustain its motion. On the basis of this assumption, the question of what moves projectiles, such as an arrow when it is no longer moved by the bowstring, naturally emerges. Aristotle’s reply, that it is the air set in motion by the original mover, was heavily criticized by Buridan on the basis of careful observation, further analysis (if the air moves the projectile, what moves the air?) as well as the analogous consideration of other types of motion, such as the ongoing rotation of a spinning wheel, which certainly cannot be explained by the motion of the surrounding air. Similar considerations apply to large bodies set in motion but no longer moved, such as a ship, which is very hard to stop, yet it is obviously not moved by the surrounding air, since those on the ship experience that the ship’s motion is resisted rather than assisted by the air.

Accordingly, Buridan assumed that these motions must be explained by an impressed force, the impetus, which is left behind in the moving body by the mover. This force is directly proportional to the heaviness of the moved body and its speed; it is decreased by resistance, and increased by the ongoing activity of the mover, but remains the same if the body once set in motion is left alone. Thus, Buridan’s theory correctly predicts that a body set in motion but left alone will exhibit what in modern physics would be described as inertial motion. Accordingly, contrary to Aristotle, Buridan should not find the hypothesis of the earth’s daily rotation absurd, since, for example, by his theory’s predictions the alleged absurdity of an arrow shot directly upward never falling back in the same place and the like should not follow. However, when he actually analyzes this problem, he finds Aristotle’s example about the arrow “more demonstrative” (magis demonstrativa, Moody, p. 229, ll. 27-28.), than the arguments of those who are willing to maintain the hypothesis of the rotation of the earth (although he does argue at length on their behalf in terms of the analogous considerations concerning travelers in a ship). For according to Buridan those who want to “save the phenomena” in accordance with this hypothesis say that the arrow falls back into the same place because the air carried by the earth by its daily rotation also carries the arrow. But Buridan rejects this “evasion” on the grounds that the vehement upward impetus of the arrow should be able to resist the lateral motion of the air. Apparently, in this argument Buridan simply failed to take into account the “lateral impetus” the arrow already has (along with the bow and the archer) on account of the earth’s movement, which, however, would have to be taken into account on the basis of his principles.

On the basis of the same principles, Buridan is obviously able to account for the acceleration of falling bodies in terms of the growing intensity of their impetus. However, by the same principles he is committed to assigning greater acceleration to heavier bodies. But, in general, Buridan’s theory remains on the level of qualitative explanation, without enabling predictions of quantifiable results that could be tested by measurements in experiments.

Nevertheless, his theory still had the tremendous significance of providing a unified explanation for the phenomena of very different motions (ranging from projectile motion to free fall, to the elastic collision of a ball, to the vibration of strings) that had been classified very differently in the traditional Aristotelian system. It was precisely this unifying perspective of Buridan’s theory that enabled him to treat even celestial motions and sublunary motions in accordance with the same mechanical principles. Accordingly, in his questions on Aristotle’s Physics (bk. VIII, q. 12), Buridan argues that, since we have no Biblical reason to assume the existence of the celestial intelligences (angels) traditionally assigned to move the heavenly spheres, celestial motions could be explained by an initial impetus given to these spheres by God, given that they have no other natural inclination and that there is no resistance to their rotation. Buridan does not mention here that this solution immediately invalidates the Aristotelian argument for the existence of a presently existing and active Prime Mover, that is, God. But he certainly was aware that these speculations took him, a lowly Master of Arts, dangerously close to questions to be determined in the Faculty of Theology. So, he immediately remarks that he does not want to assert this position, but rather leaves the determination of the issue to theologians.

Nevertheless, these speculations once and for all opened up the possibility of a unified mechanics, based on the same principles for earthly and celestial motions. Perhaps this was the most important “change in perspective” in medieval astronomy provided by Buridan’s theory, pointing in the direction of early modern celestial mechanics.

Bibliography

Primary literature

Buridan, J.: Quaestiones super octo Physicorum libros Aristotelis: Kommentar zur Aristotelischen Physik. Paris, 1509; reprint, Frankfurt am Main: Minerva, 1964.

Buridan, J.: “Questions on the Eight Books of the Physics of Aristotle, Book VIII, q. 12”, trans. Clagett, in: Clagett, M. The Science of Mechanics in the Middle Ages, Madison: Univ. Wisconsin Press, 1961, pp. 532-540.

Buridan, J.: Questiones super libros quattuor De Caelo et Mundo. Edited by E. A. Moody. Cambridge, Mass.: Medieval Academy of America, 1942.

Buridan, J.: Summulae de Dialectica, an annotated translation with a philosophical introduction by G. Klima, New Haven: Yale University Press, 2001.

Secondary literature

Crombie, A.C.: Science in the Later Middle Ages and Early Modern Times: XIII--XVII Centuries. Volume II, Medieval and Early Modern Science. New York: Anchor, 1959.

Ehrle, F.: “Der Sentenzenkommentar Peters von Candia, des Pisaner Papstes Alexanders V.,” Franziskanische Studien, 9(1925).

Grant, E.: “Scientific Thought in Fourteenth-Century Paris: Jean Buridan and Nicole Oresme,” in Cosman, M. P. and Chandler, B. (eds.): Machaut's World: Science and Art in the Fourteenth Century, Annals of the New York Academy of Sciences, Vol. 314, New York: New York Academy of Sciences, 1978, pp. 105-124.

Michael, B.: Johannes Buridan: Studien zu seinem Leben, seinen Werken und zur Rezeption seiner Theorien im Europa des späten Mittelalters. Inaugural-Dissertation. 2 vols. Berlin: Freien Universität Berlin, 1985.

Maier, A. Metaphysische Hintergründe der spätscholastischen Naturphilosophie. Rome: Edizioni di storia e letteratura, 1955.

Thijssen, J.M.M.H. and Zupko, J. (eds.): The Metaphysics and Natural Philosophy of John Buridan, Leiden/Boston/Köln: Brill, 2001.

Gyula Klima


Department of Philosophy
Fordham University


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