Aristotle thought that Nature could best be understood by observation and reason – and that all knowledge should be open to examination and subject to reason.
Science Education has shown a renewed interest in Aristotle’s works. (1) Today, theories in science are often based on abstract and mathematical models of the world. Students sometimes use the theories and equations without understanding how they were developed, their limitations, or even what problems they address. The development of an idea from Aristotle to the present would make physics more interesting and understandable. (2) Aristotle’s works are reconstructions from fragmentary notes. He had the most rudimentary of scientific equipment, his measurements were not quantitative; and he considered only things that were observable with the eye. Ignoring these limitations has caused some to distort the significance of his work, sometimes to the point of considering Aristotle an impediment to the advancement of science. However, we should not project the framework of contemporary science on Aristotle’s work – but we should read his works and examine his Natural Philosophy in the context of his times. (3)
Scientific Method: In ancient times, events in Nature had been explained as the actions of the gods. The early Greek philosophers questioned the role of the gods as the cause of events and by the fifth century B.C. the Greek philosophers, such as Socrates, had separated philosophy from theology. But, if the gods were not the cause of events, what was? Philosophers advanced explanations based on philosophical principles and mathematical forms. Aristotle found that unsatisfactory. He decided the principles of nature could be found within nature and could be discovered using careful observation and inductive reasoning. Observations must be capable of being observed by the senses and should include the four causes: the composition, the shape (or form), the motion (or change), and the end result (or purpose). Identifying the four causes insured a thorough understanding of the event. Chance or spontaneity were not considered causes. He thought all things in Nature should be open to examination and subject to reason – and he set about applying his methods to all knowledge.
Aristotle founded a school in Athens at the Lyceum which provided the world’s first comprehensive study of human knowledge from the perspective of natural philosophy. His lectures followed a pattern that formed the basis of the scientific method. They included a statement of the idea or problem, the precise definition of terms, a statement of what he and other scholars thought about the matter, the observations, arguments based on how well the ideas agreed with observation, and finally what could be concluded. His lectures notes are important as they not only show clearly his reasoning but they preserve many of the ideas of his contemporaries. (4, 5)
Physics: In his work, Physics, (6) Aristotle examined the nature of matter, space, time, and motion. He had few tools for experimentation and could not measure time or speeds. He would not allow invisible forces so his reasoning did not include gravity. Things fell to Earth and the moon circled the Earth because that was their nature. He proved that infinite linear motion and voids could not exist on Earth. Without those, he could not escape the complexities of the real world or fully understand inertia. In spite of his limitations, Aristotle made some remarkable contributions to physics and laid the groundwork for Galileo, Newton, and Einstein. He reasoned that infinite velocities could not exist, that time and movement are continuous and inseparable, and that time was even flowing, infinite, and the same everywhere at once. These are all true and a part of Einstein’s Theory of Relativity. Some consider that Aristotle’s greatest contribution to physics was his description of time.
Reading Aristotle reminds one of reading Einstein. He takes the simplest of observations and in it discovers fundamental truths. Force is a push or a pull. A horse can pull a cart and the cart pulls back on the horse and when the horse stops, the cart stops. Rest, then is the natural state of matter and the mover is acted on by that which it moves. These ideas became part of Newton’s Laws. He observed that there was both static and kinetic friction that opposed motion by studying shiphaulers. A hundred men could pull a ship but one man could not. Furthermore, he observed that the power needed to keep the ship moving depended on the force required and the speed. That is like the definition of power used today and, incidentally, something that Newton got wrong. Aristotle examined objects falling in fluids and realized friction existed there also. He found that the speed of objects increased as the weight of the object and decreased with the thickness of the fluid. This is now a part of Stoke’s Law for an object falling at its terminal velocity. He also considered what would happen if the fluid became thinner and thinner but rejected the conclusion as that would lead to a vacuum and an infinite speed, both which he considered impossibilities. Galileo allowed those impossibilities and is credited with discovering kinematics.
Cosmology: We sometimes forget that Aristotle proved the Earth was a sphere. He observed that the shadow of the Earth on the moon during an eclipse was an arc. That was not conclusive as a disk might give the same shadow. The phases of the Moon and its appearance during eclipses show it to be a sphere and the Earth might be also. As one walks toward the horizon, the horizon falls away; and, as one walks North or South, different stars appear. These are as if one is looking out from a sphere. All things made of Earth fall to Earth in such a way as to be as near the Earth as possible. A sphere is the shape that allows this as it is the shape with the smallest surface for a given volume. All things considered, the Earth must be a sphere. Interestingly, an extension of that last argument is used today to explain the erosion of mountains, surface tension, the shape of droplets, and why the moons, planets, and stars are spheres.
Aristotle concluded that since all things fall toward the center of the Earth or move round the Earth, that the Earth must be the center of the Universe. The Moon and planets move around the Earth in circular orbits but must move in circles within circles to explain the variance observed in their orbits. The stars are fixed spheres that rotate around the Earth and the Universe must be finite else the stars at the outer edge would have to move at infinite speed. Aristotle was aware that if the heavenly bodies were made of matter, that they would fly off like a rock from a sling. He therefore added to the elements a fifth element, aether, to compose the heavenly bodies. Aether could not be observed on Earth but objects composed of it could move forever in circles without friction or flying away. (7) Perhaps Aristotle should have stopped with the moon, but the planets and stars were there and needed explaining. In spite of his model’s imperfections, Aristotle gave us a universe whose laws are invariant and capable of being discovered by observation and understood by reason. Aristotle’s model of the Universe lasted almost 20 centuries without significant modification and was so compelling that Renaissance philosophers and theologians built it into church doctrine.
Scientific Revolution: However, Aristotle’s model did not fit well with new observations made by 15th century scientists. Copernicus realized that the planetary motions would be simpler and better explained if the Sun were the center of the universe. Tycho Brahe’s careful observations of planetary motions supported the Copernican model. Galileo used the first telescope to observe that Jupiter had moons that revolved around Jupiter and not the Earth. This was convincing evidence and Galileo championed a revision of Aristotle’s model. There was much resistance to the acceptance of the heliocentric model and Galileo was threatened with a charge of heresy for promoting the idea. Some people now consider Aristotle’s ideas as an impediment to the advancement of science. However, the impediment was not Aristotle’s ideas – but that Aristotle’s model of the universe had become woven into the doctrine of the Church.
Galileo’s kinematics was also in conflict with Aristotle’s work. Galileo’s experiment with falling bodies is considered as one of the ten greatest experiments of all time. He showed that a small weight fell from the Tower of Pisa at the same rate as one ten times as heavy. This was considered by some to be a triumph of Galileo’s kinematics over the simple empiricism of Aristotle. That was not, however, the whole story. Aristotle had not only examined objects falling in air but also in liquids. He found that the rate of fall in liquids increased as the weight of the object and decreased with the thickness of the fluid. This idea is consistent with Stoke’s Law for an object falling at its terminal velocity in fluids. Aristotle even had considered the case of a fluid with no thickness (a vacuum), but rejected the possibility since the speed would become infinite. However, Galileo’s experiment was performed in air and, while correct in a vacuum, Galileo’s mechanics were not exactly correct in air. Had Galileo dropped his objects from a much greater height, he would have found that the heavy object would reach the ground half again as fast as the small object. This is observable in hailstones where a large stone will strike the ground at almost twice the speed of a small stone. Galileo’s mechanics are only valid in a vacuum and even then would allow the velocity to eventually become infinite, which conflicts with Einstein’s relativity. No one has thought to criticize Galileo for that.
Scientific Progress: Many thought, and still think, that Galileo’s work was the final overthrow of Aristotelian physics and the start of a revolution allowing science to advance. That is not the case. It is just the normal progress of science that models and theories are revised as better observations and understanding occur. The Revolution was not so much an overthrow of Aristotelian Physics as it was in moving from the observable to the imaginable – and in again separating science from theology and philosophy. It is ironic that Galileo was accused of heresy for questioning the theories of a man who thought everything should be open to question and reason.
(1) ERIC. http://www.eric.ed.gov A search of the database shows 78 papers in the last three decades are about the use of Aristotle’s ideas in teaching.
(2) Stinner, A. (1994). The Story of Force: from Aristotle to Einstein. Phys. Educ., 29, 77-85.
(3) Lombardi, O. (1999). Aristotelian Physics in the Contest of Teaching Science: A Historical-Philosophical Approach. Science and Education, 8, 217-239.
(4) Durant, Will. The Story of Philosophy: The Lives and Opinions of the Great Philosophers of the Western World. 5th ed. New York: Simon and Schuster, 1949
(5) Ross, W. D. Aristotle. 5th ed. London: Methuen & Co. LTD. 1949
(6) Aristotle, Physics. Translated by R. P. Hardie and R. K. Gaye. Provided by The Internet Classics Archive. Available at
(7) Aristotle, On the Heavens. Translated by J. L. Stocks. Provided by The Internet Classics Archive. Available at http://classics.mit.edu//Aristotle/heavens.html Note: This article was originally written as the physical science contribution to Aristotle's Enduring Contribution to Biology, Physics,and Poetics by Surendra Singh, J.C. Moore, and Andrew Tadie. It was published as Aristotle on Teaching Science at the Seventh International Conference on Teacher Education, New Delhi, India (2008)
The full article is available here.
(c) 2010 J.C. Moore