Jean Buridan

French philosopher

• Born: 1300
• Birthplace: Béthune, France
• Died: 1358
• Place of death: Paris, France

A distinguished natural philosopher, Buridan wrote critical commentaries on the works of Aristotle, laid the foundations of the modern science of mechanics, and defined objectives and a methodology that separate science from philosophy and theology, making him a major figure in the development of modern science.

Early Life

Jean Buridan (zhahn bew-ree-dahn) received his early education at church schools in the diocese of Arras. His great intellectual gifts were soon manifested, and as a young cleric he studied at the University of Paris. He studied philosophy and was profoundly influenced by Ockhamism. William of Ockham, an English Franciscan, espoused nominalism, a doctrine holding that individuals are the primary reality and that universal concepts have no objective referents but are only mental descriptions for similar features among individuals. Buridan's later writings often reflect Ockham's ideas and methods.

After receiving his master of arts degree around 1320, Buridan became a lecturer in natural, metaphysical, and moral philosophy at the University of Paris. He quickly achieved recognition as a gifted philosopher, but he remained a secular cleric rather than becoming a member of a religious order, and he never sought a degree in theology. Nevertheless, he was willing to introduce theology into physical questions; for example, he argued that God could create a vacuum even though Aristotle posited the vacuum's impossibility. As a teacher and writer, Buridan was not a narrow specialist and he felt free to discuss problems as wide-ranging as the dogmas of the Christian faith and the formation of mountains.

The first documentary mention of Buridan is dated February 2, 1328, and the occasion was his appointment as university rector. The document shows that he was held in high esteem by his colleagues, and records in the Vatican indicate that benefices and honors were conferred on him several times during his successful career as a lecturer and administrator. Around 1330, he traveled south to visit the papal court at Avignon, and en route he climbed Mount Ventoux to make some meteorological observations.

In 1340, he again became rector of the University of Paris, and in that capacity he signed, on December 29, 1340, a statute strongly condemning certain members of the faculty of arts for applying strict logical analysis to scriptural texts without sufficiently considering the holy authors’ intentions. Many scholars think that this decree was directed against Nicholas of Autrecourt, a rival Scholastic philosopher whose skeptical views have since garnered for him the name “the medieval Hume.” The mild temperament discernible in many of Buridan's writings was set aside when he attacked Nicholas's errors. These condemnations, however, were not anti-Ockhamist, since Ockham's philosophy was firmly based on the principle of natural causation, which is what was impugned by Nicholas. Throughout Buridan's career, he used Ockham's doctrines to defend both natural knowledge and real secondary causes.

Life's Work

Aristotle' fourth century b.c.e. writings profoundly influenced Europeans in the thirteenth and fourteenth centuries, and Buridan's extant writings consist almost entirely of detailed commentaries on Aristotelian treatises. These writings clearly derived from his lectures at the University of Paris, whose curriculum was largely based on the study of Aristotle's works. For example, Buridan wrote commentaries on Physica (335-323 b.c.e.; Physics, 1812), Metaphysica (335-323 b.c.e.; Metaphysics, 1801), De anima (335-323 b.c.e.; On the Soul, 1812), Politica (335-323 b.c.e.; Politics, 1598), and Ethica Nicomachea (335-323 b.c.e.; Nichomachean Ethics, 1797).

Although much of his work evolved from his study of Aristotle, Buridan was not merely an explicator of Aristotelian ideas. On the contrary, he leveled some devastating attacks against this great philosopher, and he used these criticisms to develop his own ideas, which were themselves important advances in scientific and philosophical thought. This approach can be seen in Buridan's works on logic, in which, while commenting on Aristotle, he developed a method now known as logical analysis. He used this method to formulate philosophical problems as questions about the meaning and reference of terms and the truth condition of sentences. In his primer on logic, Summula de dialectica (1487; English translation, 2001), as in his other logical works (Sophismata , 1488; English translation, 1966; and Consequentie , 1493; English translation, 1985), Buridan showed himself to be a follower of logica moderna (the new logic), in which Aristotle's logic was reconstructed on new foundations. Buridan achieved this reconstruction through the theory of the supposition of terms. Medieval logicians used the word “term” to designate descriptive signs occupying the subject or predicate positions in propositions. Ockham defined supposition as the “standing for something else” of a term in a proposition. In his opinion, as in Buridan', what primarily determined the supposition, or referential use, of a subject or predicate term in a proposition was the verb.

Buridan went beyond Ockham by applying the new logic to many problems never before treated. One such problem was the analysis of statements in indirect discourse. Since the terms occurring in the subordinate clauses of sentences in indirect discourse purport to designate what actually is said to be known, the question of what such terms denote boils down to the question of what kinds of entities constitute the object of knowledge. Do these terms stand for really existing individual things or Platonic essences or simply the words themselves?

Buridan's most extensive treatment of this problem is found in Sophismata, a work devoted to the analysis of paradoxical statements that appear to be both true and false. The famous “liar” paradox is an example: Is the statement “What I am now saying is false” true or false? According to Aristotelian logic, this statement is true if it is false and false if it is true. Buridan thought that the person who makes that statement and says nothing else really is saying something false, because this sentence has to be considered together with the circumstances of its utterance, and one of these circumstances is that sentences cannot be both true and false. Thus, in this case the sentence and its circumstances make the statement false.

In philosophy, Buridan was a moderate nominalist; he supported the condemnation of both the radical Ockhamism of Nicholas and the extreme Aristotelianism of the followers of Averroës. Among his philosophical discussions, Buridan is best known for his theory of the relationship of will and reason. He proposed that a person must will what is revealed to reason as the greater good but stated that the will is free to delay choice until the reason has more extensively inquired into the values and motives involved. The classic illustration of this analysis is the parable of “Buridan's ass,” a story not found in the extant writings. An ass is situated between two equidistant and equivalent bundles of hay. Because the ass has no reason to choose one bale over the other, he would remain in perpetual indecision and starve to death. Later philosophers attacked Buridan's theory of the will. In their view, when reason can find no preference, the will is still capable of decision when it is clear that delay is pointless, stupid, or even dangerous.

Despite his perceptive logical and philosophical analyses, Buridan made his most important contributions in science. Aristotle had defined science as the knowledge of universal and necessary conclusions made by demonstration from necessary though indemonstrable premises. Buridan, on the other hand, sharply distinguished between premises determined logically, through definitions of the terms, and those determined empirically, through inductive generalization from conditional evidence. He therefore rejected the thesis, common among many Scholastic philosophers, that the principles of physics are necessary in the sense that their contradictories are logically impossible. Buridan did not require the same logical rigor from the scientist as from the mathematician. According to him, if scientific truths could be imposed under pain of contradiction, then physical science would be destroyed. Through this analysis he was able to concede the possibility of God's interference with the natural order while still excluding supernatural events as irrelevant to the scientific enterprise.

In his treatment of physics and cosmology, Buridan accepted Aristotle's ideas as a basic framework for natural philosophy, but he also entertained alternative ideas as both logically possible and empirically preferable to explain certain phenomena. His most incisive criticism was directed against Aristotle's account of motion. An obvious weakness of Aristotle's theory was its inability to explain projectile motion satisfactorily. For Aristotle, a thrown object required an external moving cause continuously in contact with it. He theorized that the air, disturbed by the violent motion of throwing the projectile, kept pushing the object forward for a time. Buridan first refuted Aristotle's theory by several empirical arguments; for example, he showed that disturbing the air was not sufficient to move the projectile. He then proposed his theory of impetus as a solution.

Impetus, to Buridan, was a motive force impressed by the thrower on the projectile. He regarded this impressed force as permanent and believed that were it not for air resistance and gravity, impetus would maintain the projectile at a uniform speed. Buridan also quantified impetus as the product of the amount of matter and the speed, the same quantities defining momentum in Sir Isaac Newton's physics, although Newton's momentum is a measure of the effect of a body's motion whereas Buridan's impetus is a cause of motion. Also significant for later physics is Buridan's statement that impetus is an “enduring reality,” for it suggests Newton's law of inertia: An object, once set in motion, tends to remain in motion at a uniform speed. An important difference between Newton's inertia and Buridan's impetus is that impetus would persist indefinitely for an object moving both in a circle and in a straight line, whereas Newton's momentum would persist only in a straight line and would need a force to bend it into a circle.

Buridan used impetus to explain many phenomena: the acceleration of an object falling to earth, the vibration of plucked strings, the bouncing of balls, and the everlasting rotations of heavenly bodies. This last application is the most important one, and Pierre Duhem, the great French physicist, dated the beginning of modern science to Buridan's rejection of Intelligences as movers of the heavenly bodies. Buridan believed that the heavenly bodies, having been put in motion by God, continued to move because of the impetus God impressed on them; they consequently required no everlastingly active angels to keep them moving. Buridan explained rotational motion by a rotational impetus analogous to the rectilinear impetus for projectile motion. Galileo Galilei held similar views; it was not until Newton that the movements of heavenly and earthly bodies were correctly explained.

In the light of the great changes that Nicolaus Copernicus would cause in astronomy two centuries later, it is interesting that Buridan himself investigated the question of whether Earth is at rest. He believed that the daily motion of the stellar sphere and the planets could be explained by assuming either a stationary heaven and rotating Earth or the reverse. In other words, he recognized that the problem was one of relative motion. To support the theory of a rotating Earth, Buridan stressed, in typical Ockhamist manner, the desirability of explaining the phenomena by the simplest means possible. Since it was simpler to move the smaller Earth than the much larger stellar sphere, it seemed reasonable to attribute rotation to Earth while leaving the stellar sphere at rest. Despite this and other arguments favorable to a daily terrestrial motion, Buridan finally opted for a nonrotating Earth because, in his judgment, a rotating Earth could not explain why an arrow shot vertically into the air fell back to its origin rather than far to the west.

Although Buridan believed that Earth did not rotate, he nevertheless did not believe it was perfectly stationary. Indeed, he thought that Earth experienced incessant, though slight, motions that arose from continual shifts of Earth's center of gravity, caused by the redistribution of matter on its surface. Buridan explained that streams and rivers carried material from the mountains to the sea, and in this way the elevated regions of Earth became lighter and the watery regions heavier. His explanation is similar to the modern theory of isostasy, which plays a major role in physical geology.

It is not known which work written by Buridan was his last. The final documentary mention of him is dated July 12, 1358, in a statute in which his name appears as a witness to an agreement between the Picard and English students and teachers of the University of Paris. Buridan, who came from this region of northern France, represented the Picards. It is possible, though there is no real evidence to support it, that he fell victim to the Black Death , which in the late 1350's took the lives of many of those who had survived its first outbreak in 1348-1349.

Significance

To many historians of science, Buridan is the key figure in the development of medieval dynamics and an important precursor of modern mechanics. He successfully challenged Aristotle's theory of motion and proposed an alternative dynamics that had potentially revolutionary implications. Unfortunately, he did not generalize impetus into a theory of universal inertial mechanics. Although he used impetus to explain both terrestrial and celestial motion, he never tried to formulate a single mechanics for the whole universe because he accepted the Aristotelian dichotomy between terrestrial and celestial bodies. Buridan's ideas on terrestrial and celestial movements were developed by Albert of Saxony and Nicole d’Oresme, and his theory of impetus came to have wide acceptance in fifteenth and sixteenth century France, England, Germany, and Italy.

Other scholars see Buridan's importance more in the questions he raised than in the answers he proposed. Even when his specific contributions to physics were forgotten, the influence of his conception of scientific evidence and method lived on. In particular, he helped eliminate explanations in terms of final causes from physics. His work marks a shift from a metaphysical to an empirical attitude toward scientific problems. He vindicated natural philosophy as a field of study in its own right, and he defined the objectives and methodology of science in a way that guaranteed its autonomy with regard to theology and philosophy. In this sense, Duhem is correct in saying that Buridan's work marks the start of modern science.

Bibliography

Clagett, Marshall. The Science of Mechanics in the Middle Ages. Madison: University of Wisconsin Press, 1959. Presents documentary material on which to base studies of medieval science, and contains excerpts and helpful discussions of several works by Buridan on mechanics and cosmology.

Dijksterhuis, E. J. The Mechanization of the World Picture: Pythagoras to Newton. Translated by C. Dikshoorn. Reprint. Princeton, N.J.: Princeton University Press, 1986. This classic work is a detailed account of the origins and development of the physical sciences.

Duhem, Pierre. Medieval Cosmology: Theories of Infinity, Place, Time, Void, and the Plurality of Worlds. Translated and edited by Roger Ariew. Chicago: University of Chicago Press, 1985. Presents excerpts from a discussion of Buridan and others that demonstrates the sophistication of medieval physics and cosmology.

Grant, Edward. A Source Book in Medieval Science. Cambridge, Mass.: Harvard University Press, 1974. Part of a series in classical papers that have shaped the history of various sciences. Several selections have been translated into English from Buridan’s works on natural philosophy and are presented with commentary and annotations.

Lindberg, David C., ed. Science in the Middle Ages. Chicago: University of Chicago Press, 1978. Analysis of major aspects of the medieval scientific enterprise in some detail and a discussion of Buridan’s work in chapters on medieval philosophy, mechanics, and cosmology.

Moody, Ernest A. Studies in Medieval Philosophy, Science, and Logic: Collected Papers, 1933-1969. Berkeley: University of California Press, 1975. A collection of several of the author’s influential papers on Buridan, among them “John Buridan on the Habitability of the Earth” and “Buridan and a Dilemma of Nominalism.”

Thijssen, J. M. M. H., and Jack Zupko, eds. The Metaphysics and Natural Philosophy of John Buridan. Boston: Brill, 2001. An analysis of Buridan’s metaphysics, physics, and natural philosophy. Includes an extensive bibliography and an index.

Zupko, Jack. John Buridan: Portrait of a Fourteenth-Century Arts Master. Notre Dame, Ind.: University of Notre Dame Press, 2003. A survey of Buridan’s science of logic; of his views on the question of bodies and souls, knowledge, freedom, and natural science; and of his legacy in the history of philosophy and science.