Why don't we learn Buridan's laws of motion?

Question

My question is why has Jean Buridan faded into obscurity while Newton is venerated as a God by scientists? Here is a description of Buridan's impetus theory:

The concept of inertia was alien to the physics of Aristotle. Aristotle, and his peripatetic followers, held that a body was only maintained in motion by the action of a continuous external force. Thus, in the Aristotelian view, a projectile moving through the air would owe its continuing motion to eddies or vibrations in the surrounding medium, a phenomenon known as antiperistasis. In the absence of a proximate force, the body would come to rest almost immediately.

Jean Buridan, following in the footsteps of John Philoponus and Avicenna, proposed that motion was maintained by some property of the body, imparted when it was set in motion. Buridan named the motion-maintaining property impetus. Moreover, he rejected the view that the impetus dissipated spontaneously (this is the big difference between Buridan's theory of impetus and his predecessors), asserting that a body would be arrested by the forces of air resistance and gravity which might be opposing its impetus. Buridan further held that the impetus of a body increased with the speed with which it was set in motion, and with its quantity of matter. Clearly, Buridan's impetus is closely related to the modern concept of momentum. Buridan saw impetus as causing the motion of the object. Buridan anticipated Isaac Newton when he wrote:

...after leaving the arm of the thrower, the projectile would be moved by n impetus given to it by the thrower and would continue to be moved as long as the impetus remained stronger than the resistance, and would be of infinite duration were it not diminished and corrupted by a contrary force resisting it or by something inclining it to a contrary motion (Questions on Aristotle's Metaphysics XII.9).

Buridan used the theory of impetus to give an accurate qualitative account of the motion of projectiles but he ultimately saw his theory as a correction to Aristotle, maintaining core peripatetic beliefs including a fundamental qualitative difference between motion and rest.

The theory of impetus was also adapted to explain celestial phenomena in terms of circular impetus.

This sounds a lot to me like some of the theories that made Newton a household name.

http://en.wikipedia.org/wiki/Jean_Buridan

Answer 1

The next to last sentence has all the reasons in a nutshell:"Buridan used the theory of impetus to give an accurate qualitative account of the motion of projectiles but he ultimately saw his theory as a correction to Aristotle". Buridan's account, as Aristotle's or Avicenna's before him, was qualitative, he never put it into equations, which would allow for predictions and experimental verification. It only applied to projectiles, there was no notion of universally valid dynamical laws that governed motion in general, so no "laws of motion". There was a separate "circular impetus" to explain celestial motions, and "natural places" to explain gravity on Earth. And finally, being a correction to Aristotle, Buridan's theory retained its central problem, the murky and/or erroneous relation between speed and force, with little understanding of the role of acceleration.

This being said, I do agree that the impetus theory played a positive role in the genesis of classical mechanics, and deserves to be better known. It directly influenced Descartes, for example, and played a role in the discovery of the conservation of momentum law. Its roots can be traced back to Hipparchus, the father of astronomy, and medieval authors learned it from a commentary of John Philoponus, who by the way also anticipated the modern idea of empirical inquiry. Avicenna introduced the idea that projectile impetus can be self-degrading, which makes his description comparable to the modern one in the decelerating frame attached to the projectile. Franco's paper gives a good overview of the history of the impetus theory.

Answer 2

I have not read Buridan, but I am sure he was a philosopher, like Aristotle. The laws of nature are usually not named after philosophers. Philosophers can state all kinds of opinions, but this does not really add to the body of positive knowledge about nature. The difference between Newton and Buridan, is that Newton not just stated an opinion, but developed a useful theory which can predict the motion of planets, and projectiles and almost everything else. Without this, philosophical opinions about nature are worthless. (Even if the later development of science later proves that philosophers accidentally guessed something correctly).

You may compare this with atoms. Democritus and Leucippus speculated about some atoms. There was no proofs whatsoever and no concrete predictions which could be tested. Other philosophers speculated that atoms do not exist. Such speculations can go on forever without any useful consequences. When atoms were finally incorporated into a scientific theory (in the end of 19th century) nobody teaches this as a "Leucippus-Democritus theory". Same with Buridan.

There are many cases when philosophers had wrong opinions, the most famous examples are Aristotle and Hegel (but also Marx and Engels:-) Sometimes they accidentally guess. The problem with philosophy is that it has no means to test, to verify a statement.

Answer 3

Clearly, Buridan, rector of the university of Paris, made all the basic breakthroughs in dynamics: he viewed force, vectorial force, as what changed impetus, and only force could modify impetus (be it a force from air resistance, or from gravity). Impetus was written by Buridan as equal to (quantity of matter)(velocity). This is the modern definition of momentum. Remember, that was before equations...

Without force applied, impetus would go on and on, either straight, or circular from gravity: thus the planets kept on turning around (Buridan observed that the heliocentric theory was as compatible with observations as the geocentric theory; his student Oresme added that it was more likely that the Earth moved and rotated than all the stars doing so, because the latter were obviously much more distant and massive; impetus theory insured the air won't be left behind).

Buridan also exposed the essence of the experimental method, decided by observing phenomena, he said. What was not compatible with phenomena, had to be ruled out (that meant Aristotle’s physics was ruled out). Buridan's student Oresme demonstrated (geometrically) the first non trivial theorems of calculus applied to motion.

First, as rector of the university of Paris, Buridan has had to generalize, and formally enable, in 1340 CE, a notion of "object of knowledge" as potentially unobservable... (Impetus, heliocentrism, etc. were not directly observable…) That was theologically dangerous.

All this was all the more remarkable as Buridan, Oresme (who became dean of the cathedral of Rouen, then a bishop!) had to stay clear from the murderous Inquisition (which considered Aristotle's physics as god-given). Thus some apparent contradictions in Buridan and Oresme, to assuage the Inquisition.

However, more than a century after his death, all of Buridan's works were outlawed on the pain of death by the Catholic church (all Buridan;s works were put in the Index Librorum Prohibitorum, the Index of Prohibited Books of the Roman Office of the Inquisition)... except in Eastern Europe, which was furious from the burning alive of Jan Hus, rector of the university of Prague in 1415 CE. In Krakow Buridan was mandatory reading at the university, thus teaching Buridan’s heliocentric theory to the young Copernicus...

Ignoring Buridan while just focusing on Newton, should be viewed as a sneaky way to glorify the Anglosphere. That is unfair not just to Buridan and another dozen intervening major physicists, over those three centuries in between. It's also unfair to the process of serious scientific revolution, and the enormous boldness necessary to put it in motion.

Answer 4

I agree with Patrice Ayme on the topic of Buridan and will add that one major role of those employed in a teaching role at a university should be to provide comments and ideas that are helpful to the progress of thought. In this he was clearly successful in spite of religious leaders who had immense power to destroy those who opposed them. The fact that those leaders of society were religious leaders enables people in the modern world to easily criticise but religious viewpoints aren't the only way that free thought may be discriminated against.

Philosophy isn't as highly regarded as it was a few decades ago but I wish it was. Modern thought on many topics including science, economic and perhaps even political theory may leave us with many conflicting ideas but sometimes a lack of real direction towards problem solving. Theories have the value of creating a framework that can hopefully be tested but conversely can be held back by the need to exist within the framework of pre-existing theories. What about laws rather than theories of explanation, like the laws of thermodynamics, for example? Perhaps it's possible to explain gravity, for example, by using the laws of thermodynamics, but such an explanation is limited in its use to science unless it exists within a framework of measurable results. To provide the latter may well require a total rethink on certain ideas, definitions or theories. Perhaps to continue the thinking on what controls movement of mass we need philosophers to question those ingrained ideas on basic notions like "What is a force?", for example and is it worth having another look at the relationship between energy and momentum.

Einstein created a new framework to connect mass to the phenomenon that we comprehend as gravity. He also used F = ma in creating a new way to define energy in terms of mass and the speed of light yet he didn't so much say what caused these properties to exist. It was more about explaining what we already knew was happening in another measurable way, which in turn led to numerous conclusions of immense value. Things like relativity were already on the discussion table at least as far back as Galileo but mathematically minded scientists like Newton just didn't have a known framework for approaching the necessary measurements, let alone calculations.

Answer 5

Newton is 'venerated' for his synthesis of the laws of motion, the theory of gravity and the calculus. Virtually everything he did had some antecedent in work earlier than his, but he put it all together.

Buridans name 'has faded into obscurity' not because of the lack of the importance of his work, but simply because the history of science is not taken as seriously as science itself. What is presented as such in textbooks is merely the barest smattering of such a history.

By the way, it's not true that the notion of 'inertia' was 'unknown' to Aristotle. This is a common misconception. He would not have phrased it that way. Nevertheless, he did develop the notion of 'natural motion' which is the antecedent notion from which inertia developed. Moreover, it's also incorrect to say that he wrote 'a body is only maintained in motion so long as a continuous force is applied'. Or rather, the interpretation is incorrect.

What he said, was that real change occurs only and for as long as force is applied (and the body is potentially capable of changing). The converse, of course, is that when no force is applied, no change occurs.

The mistake here is to consider change of position to be actual change. The actual change is not change in position, but change in velocity - that is acceleration.

What we then see is that Aristotle elaborated a general theory of change, and then Newton as well as many others preceding him, specialised this for actual physical motion.